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1. Multi-Messenger observations of the Fermi-LAT blazar 4FGL J0658.6+0636 consistent with an IceCube high-energy neutrino

Author

David R. Williams, Antoine Kouchner, K. A. Farrell, Alasdair E. Gent, V. V. Vassiliev, Fabian Schüssler, H. A. Peña-Herazo, Georgios Paraschos, R. Shang, D. S. Hanna, Q. Feng, John L. Quinn, D. Ribeiro, Daniel Nieto, A. Brill, Giacomo Bonnoli, M. Kertzman, Lucy Fortson, Yong Sheng, Olivier Hervet, T. B. Humensky, Francesco Massaro, S. O'Brien, Alessio Berti, M. J. Lang, donggeun tak, Teddy Cheung, Suvi Gezari, Joern Wilms, A. D. Falcone, P. T. Reynolds, Miguel Perez-Torres, Andrea Tramacere, Reshmi Mukherjee, G. M. Foote, Binita Hona, C. Giuri, Raniere de Menezes, P. Kaaret, I. Sadeh, Frank J. Masci, Emilio Fernandez-Garcia, W. Jin, Wystan Benbow, Uwe Bach, R. R. Prado, P. Moriarty, Jonas Heßdörfer, M. Pohl, Matthias Kadler, Steven Hämmerich, Gernot Maier, G. H. Sembroski, Andrea Gokus, R. A. Ong, M. Capasso, Ivan Agudo, Marcos Santander, C. E. McGrath, T. J. Williamson, A. J.R. Weinstein, E. Roache, A. Archer, Jorge Otero-Santos, Simone Garrappa, Alex Kraus, G. H. Gillanders, A. J. Castro-Tirado, Alexis Coleiro, Jodi Christiansen, Jamie Holder, K. Ragan, Meenakshi Rajagopal, A. N. Otte, Alessandro Paggi, K. Pfrang, Orel Gueta, Marcello Giroletti, Cristina Nanci, Javier Moldon, M. Nievas-Rosillo, Elisa Bernardini, C. Adams, Werner Colmar, Y. D. Hu, J. A. Ryan, Richard Walters, M. Lundy, Florian Eppel, Tobias Kleiner, R. Sanchez-Ramirez, J. H. Buckley, A. J. Chromey, Amy Furniss, Charlotte Ward, Konstancja Satalecka, E. Pueschel, Manel Errando, Sara Buson, S. Kumar, S. Patel, M. D. Caballero-Garcia, and Marco Ajello

Subjects
Physics, High energy, Astrophysics, Neutrino, Blazar, Fermi Gamma-ray Space Telescope
Published
2021
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2. VERITAS Observations of the Galactic Center Region at Multi-TeV Gamma-Ray Energies

Author

S. O'Brien, donggeun tak, E. Roache, K. A. Farrell, V. V. Vassiliev, John L. Quinn, D. Ribeiro, J. H. Buckley, K. Ragan, P. Kaaret, A. Archer, A. J. Chromey, M. Nievas-Rosillo, G. H. Gillanders, Reshmi Mukherjee, David Kieda, Jodi Christiansen, C. Giuri, James M. Ryan, M. Kertzman, Olivier Hervet, Amy Furniss, A. Brill, I. Sadeh, Lucy Fortson, Marcos Santander, Binita Hona, D. S. Hanna, M. J. Lang, E. Pueschel, Wystan Benbow, A. D. Falcone, Orel Gueta, Q. Feng, P. Moriarty, M. Capasso, W. Jin, Daniel Nieto, Gernot Maier, Martin Pohl, T. J. Williamson, A. N. Otte, C. E. McGrath, K. Pfrang, A. J.R. Weinstein, R. Shang, P. T. Reynolds, G. M. Foote, Jamie Holder, R. A. Ong, R. R. Prado, David A. Williams, Tobias Kleiner, G. H. Sembroski, J. A. Ryan, M. Lundy, C. Adams, T. B. Humensky, Manel Errando, S. Kumar, S. Patel, and Alasdair E. Gent

Subjects
High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Supermassive black hole, Astrophysics::High Energy Astrophysical Phenomena, Galactic Center, Astrophysics::Instrumentation and Methods for Astrophysics, Gamma ray, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Light curve, law.invention, Telescope, Sagittarius A, law, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics::Galaxy Astrophysics, Cherenkov radiation, Zenith
Abstract

The Galactic Center region hosts a variety of powerful astronomical sources and rare astrophysical processes that emit a large flux of non-thermal radiation. We present the analysis of the very-high-energy gamma-ray emission above 2 TeV of the region around the Galactic Center known as the Central Molecular Zone using 125 hours of data taken with the VERITAS imaging-atmospheric Cherenkov telescope between 2010 and 2018. This analysis employs new shower reconstruction algorithms and instrument response functions optimized for data taken at large zenith angles such as the Galactic Center sources. We report positions and spectra for point sources VER J1745-290, G0.9+0.1, and HESS J1746-285, along with a light curve for VER J1745-290, the brightest source in the region consistent with the position of the supermassive black hole Sagittarius A*. We also measure the spectrum of the diffuse emission from the Galactic Center ridge region, which has been claimed as evidence of a Galactic PeVatron., Contribution to the Proceedings of the 37th International Cosmic Ray Conference (ICRC 2021), Berlin, Germany

Published
2021
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3. Status of the VERITAS Stellar Intensity Interferometry (VSII) System

Author

P. Moriarty, Alasdair E. Gent, James Ryan, R. Shang, Daniel Nieto, E. Roache, M. Capasso, M. Kertzman, T. J. Williamson, Davis Jonathan, David R. Williams, K. Ragan, S. O'Brien, Wystan Benbow, M. J. Lang, Marcos Santander, P. Kaaret, M. Pohl, Reshmi Mukherjee, C. E. McGrath, I. Sadeh, A. Brill, K Matthews Nolan, A. J.R. Weinstein, Jamie Holder, C. Giuri, Q. Feng, John L. Quinn, A. Archer, D. Ribeiro, M. Nievas-Rosillo, Sameer Patel, Orel Gueta, A. D. Falcone, Manel Errando, G. H. Sembroski, Gernot Maier, S. Kumar, R. R. Prado, D. S. Hanna, C. B. Adams, David Kieda, T. B. Humensky, S. Patel, LeBohec Tugdual, R. A. Ong, G. H. Gillanders, Olivier Hervet, K. A. Farrell, V. V. Vassiliev, Lisa Mike, Lucy Fortson, Jodi Christiansen, Tobias Kleiner, G. M. Foote, J. H. Buckley, A. J. Chromey, donggeun tak, A. N. Otte, K. Pfrang, W. Jin, M. Lundy, Binita Hona, Amy Furniss, E. Pueschel, and P. T. Reynolds

Subjects
Physics, Interferometry, Astronomy, Intensity (physics)
Published
2021
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4. Very High Energy Gamma-ray Emission from the Binary System LS I +61 303

Author

G. M. Foote, S. O'Brien, W. Jin, Tobias Kleiner, R. Shang, Orel Gueta, R. R. Prado, P. Kaaret, P. T. Reynolds, E. Pueschel, John L. Quinn, I. Sadeh, C. B. Adams, James Ryan, D. Ribeiro, David R. Williams, M. Pohl, Gernot Maier, Jodi Christiansen, Q. Feng, T. B. Humensky, M. Lundy, Marcos Santander, Lucy Fortson, P. Moriarty, Olivier Hervet, C. E. McGrath, M. Capasso, M. Kertzman, A. J.R. Weinstein, A. Brill, A. N. Otte, Daniel Nieto, David Kieda, T. J. Williamson, K. Pfrang, Manel Errando, S. Kumar, R. A. Ong, S. Patel, G. H. Sembroski, J. H. Buckley, M. Nievas-Rosillo, Binita Hona, D. S. Hanna, K. A. Farrell, V. V. Vassiliev, Sameer Patel, donggeun tak, Amy Furniss, A. Archer, E. Roache, A. J. Chromey, G. H. Gillanders, Reshmi Mukherjee, C. Giuri, Alasdair E. Gent, K. Ragan, M. J. Lang, A. D. Falcone, Jamie Holder, and Wystan Benbow

Subjects
Physics, High energy, Gamma ray, Binary system, Computational physics
Published
2021
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5. The VERITAS-Stellar Intensity Interferometry (VSII) survey of Stellar Diameters

Author

James Ryan, Wystan Benbow, Mike Lisa, G. M. Foote, P. Moriarty, C. B. Adams, Lucy Fortson, Amy Furniss, Q. Feng, R. A. Ong, P. T. Reynolds, M. Capasso, M. Kertzman, Manel Errando, E. Pueschel, Orel Gueta, Daniel Nieto, T. J. Williamson, S. Kumar, T. B. Humensky, M. Nievas-Rosillo, G. H. Sembroski, S. Patel, Nolan Matthews, Sameer Patel, Alasdair E. Gent, J. H. Buckley, A. N. Otte, D. S. Hanna, Marcos Santander, M. Lundy, Tugdual LeBohec, P. Kaaret, A. Archer, K. Pfrang, Gernot Maier, A. J. Chromey, S. O'Brien, Binita Hona, C. E. McGrath, donggeun tak, Olivier Hervet, David R. Williams, Reshmi Mukherjee, A. Brill, G. H. Gillanders, A. J.R. Weinstein, Jonathan Davis, Jodi Christiansen, I. Sadeh, C. Giuri, R. Shang, Tobias Kleiner, E. Roache, David Kieda, M. Pohl, K. Ragan, K. A. Farrell, V. V. Vassiliev, John L. Quinn, D. Ribeiro, R. R. Prado, W. Jin, Jamie Holder, M. J. Lang, and A. D. Falcone

Subjects
Telescope, Physics, Interferometry, Stars, Cardinal point, Optical wavelength, law, IACT, Astrophysics, Cherenkov radiation, Intensity (physics), law.invention
Abstract

The VERITAS Imaging Air Cherenkov Telescope (IACT) array was augmented in 2019 with high-speed focal plane electronics to allow its use for Stellar Intensity Interferometry (SII) observations. Since January 2019, The VERITAS Stellar Interferometer (VSII) recorded more than 250 hours of moonlit observations on 39 different bright stars and binary systems ($m_V < 3.74$ ) at an effective optical wavelength of 416 nm. These observations resulted in the measurement of the diameters of several stars with better than 5\% resolution. This talk will describe the status of the VSII survey and analysis.

Published
2021
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6. VERITAS Observations of the Galactic Center Region at Multi-TeV Gamma-Ray Energies

Author

G. H. Sembroski, M. Lundy, P. Moriarty, Lucy Fortson, T. B. Humensky, S. Schlenstedt, Martin Pohl, Gernot Maier, Alasdair E. Gent, M. K. Daniel, Manel Errando, S. P. Wakely, A. Weinstein, J. P. Finley, Reshmi Mukherjee, M. Kertzman, C. Giuri, Jodi Christiansen, K. Ragan, Robert Brose, P. Kaaret, A. N. Otte, A. D. Falcone, K. Pfrang, Marcos Santander, D. S. Hanna, R. Shang, Wystan Benbow, David Kieda, G. H. Gillanders, Olivier Hervet, R. R. Prado, M. Buchovecky, John L. Quinn, D. Ribeiro, S. O'Brien, E. Roache, David A. Williams, R. A. Ong, S. Kumar, A. Brill, Daniel Nieto, Q. Feng, Amy Furniss, James Ryan, F. Krennrich, P. T. Reynolds, M. Nievas-Rosillo, E. Pueschel, B. Stevenson, A. J. Chromey, C. B. Adams, G. Hughes, Jamie Holder, M. J. Lang, Gordon T. Richards, N. Kelley-Hoskins, W. Jin, and M. Capasso

Subjects
010504 meteorology & atmospheric sciences, accelerator, High-energy astronomy, Astrophysics::High Energy Astrophysical Phenomena, atmosphere [Cherenkov counter], VHE [gamma ray], FOS: Physical sciences, Cosmic ray, Astrophysics, power spectrum, 01 natural sciences, emission [gamma ray], HESS, 0103 physical sciences, supernova, black hole, TeV, cloud, composite, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Supermassive black hole, Spectral index, background, Galactic Center, Gamma ray, Astronomy and Astrophysics, Light curve, flux, Supernova, 13. Climate action, Space and Planetary Science, cosmic radiation, ddc:520, VERITAS, galaxy, Astrophysics - High Energy Astrophysical Phenomena
Abstract

The Galactic Center (GC) region hosts a variety of powerful astronomical sources and rare astrophysical processes that emit a large flux of non-thermal radiation. The inner 375 pc x 600 pc region, called the Central Molecular Zone, is home to the supermassive black hole Sagittarius A*, massive cloud complexes, and particle accelerators such as supernova remnants. We present the results of our improved analysis of the very-high-energy (VHE) gamma-ray emission above 2 TeV from the GC using 125 hours of data taken with the VERITAS imaging-atmospheric Cherenkov telescope between 2010 and 2018. The central source VER J1745-290, consistent with the position of Sagittarius A*, is detected at a significance of 38 standard deviations above the background level $(38\sigma)$, and we report its spectrum and light curve. Its differential spectrum is consistent with a power law with exponential cutoff, with a spectral index of $2.12^{+0.22}_{-0.17}$, a flux normalization at 5.3 TeV of $1.27^{+0.22}_{-0.23}\times 10^{-13}$ TeV-1 cm-2 s-1, and cutoff energy of $10.0^{+4.0}_{-2.0}$ TeV. We also present results on the diffuse emission near the GC, obtained by combining data from multiple regions along the GC ridge which yield a cumulative significance of $9.5\sigma$. The diffuse GC ridge spectrum is best fit by a power law with a hard index of 2.19 $\pm$ 0.20, showing no evidence of a cutoff up to 40 TeV. This strengthens the evidence for a potential accelerator of PeV cosmic rays being present in the GC. We also provide spectra of the other sources in our field of view with significant detections, composite supernova remnant G0.9+0.1 and HESS J1746-285., Comment: 19 pages, 8 figures, Accepted for publication in Astrophysical Journal

Published
2021
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7. Probing the Properties of the Pulsar Wind in the Gamma-Ray Binary HESS J0632+057 with NuSTAR and VERITAS Observations

Author

P. Kaaret, R. Mukherjee, M. Nievas-Rosillo, N. Kelley-Hoskins, C. Giuri, Gernot Maier, E. Roache, Ralph Bird, David Kieda, R. A. Ong, Kaya Mori, K. Ragan, D. S. Hanna, Orel Gueta, Abraham D. Falcone, A. Brill, P. Wilcox, C. J. Hailey, Tarek M. Hassan, M. Kertzman, David A. Williams, A. N. Otte, Amy Furniss, G. H. Sembroski, A. Weinstein, Marcos Santander, A. J. Chromey, I. Sadeh, Robert Brose, Maria Krause, N. H. Park, I. Sushch, Wystan Benbow, J. P. Finley, T. J. Williamson, Jodi Christiansen, O. Hervet, A. Archer, A. Petrashyk, Jamie Holder, P. T. Reynolds, E. Pueschel, M. J. Lang, S. O'Brien, A. Gent, G. H. Gillanders, Q. Feng, Lucy Fortson, Shifra Mandel, D. Ribeiro, Gordon T. Richards, John L. Quinn, A. Wilhelm, Weiguang Cui, K. Pfrang, Daniel Nieto, G. Hughes, Martin Pohl, T. B. Humensky, S. Schlenstedt, P. Moriarty, M. Buchovecky, and R.R. Prado

Subjects
High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Spectral index, 010504 meteorology & atmospheric sciences, Be star, Astrophysics::High Energy Astrophysical Phenomena, Gamma ray, FOS: Physical sciences, Spectral density, Astronomy and Astrophysics, Electron, Astrophysics, Compact star, Light curve, 01 natural sciences, Pulsar, 13. Climate action, Space and Planetary Science, 0103 physical sciences, ddc:520, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences
Abstract

HESS J0632+057 is a gamma-ray binary composed of a compact object orbiting a Be star with a period of about $315$ days. Extensive X-ray and TeV gamma-ray observations have revealed a peculiar light curve containing two peaks, separated by a dip. We present the results of simultaneous observations in hard X-rays with NuSTAR and in TeV gamma-rays with VERITAS, performed in November and December 2017. These observations correspond to the orbital phases $\phi\approx0.22$ and $0.3$, where the fluxes are rising towards the first light-curve peak. A significant variation of the spectral index from 1.77$\pm$0.05 to 1.56$\pm$0.05 is observed in the X-ray data. The multi-wavelength spectral energy distributions (SED) derived from the observations are interpreted in terms of a leptonic model, in which the compact object is assumed to be a pulsar and non-thermal radiation is emitted by high-energy electrons accelerated at the shock formed by the collision between the stellar and pulsar wind. The results of the SED fitting show that our data can be consistently described within this scenario, and allow us to estimate the magnetization of the pulsar wind at the location of the shock formation. The constraints on the pulsar-wind magnetization provided by our results are shown to be consistent with those obtained from other systems., Comment: Accepted for publication in The Astrophysical Journal

Published
2020
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8. VERITAS Discovery of VHE Emission from the Radio Galaxy 3C 264: A Multi-Wavelength Study

Author

A. Brill, Alasdair E. Gent, James Ryan, Manel Errando, E. T. Meyer, Gordon T. Richards, Olivier Hervet, M. Kertzman, E. Roache, A. Archer, T. T.Y. Lin, K. Ragan, R. A. Ong, S. O'Brien, B. Stevenson, D. S. Hanna, G. Hughes, Wystan Benbow, P. Moriarty, Matthew L. Lister, C. B. Rulten, M. Lundy, K. Ramirez, Karlen Shahinyan, T. J. Williamson, Tarek M. Hassan, A. Wilhelm, David Kieda, Daniel Nieto, M. Nievas-Rosillo, A. C. Sadun, Jodi Christiansen, Jamie Holder, Marcos Santander, P. T. Reynolds, K. Pfrang, John L. Quinn, D. Ribeiro, R. Shang, M. J. Lang, Gernot Maier, A. D. Falcone, A. Weinstein, M. Pohl, S. P. Wakely, R. R. Prado, M. K. Daniel, P. Fortin, Ralph Bird, David A. Williams, Orel Gueta, P. Wilcox, J. H. Buckley, S. S. Scott, A. J. Chromey, Michael T. Carini, F. Krennrich, M. Georganopoulos, Reshmi Mukherjee, C. Giuri, Q. Feng, G. H. Gillanders, T. B. Humensky, P. Kaaret, Lucy Fortson, M. Buchovecky, G. H. Sembroski, E. Pueschel, Vladimir Vassiliev, and Amy Furniss

Subjects
010504 meteorology & atmospheric sciences, Radio galaxy, atmosphere [Cherenkov counter], Astrophysics, cosmic background radiation, power spectrum, 01 natural sciences, law.invention, Astrophysical jet, law, pixel, ultraviolet, black hole, optical, dimension: 2, 010303 astronomy & astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), photon, 2 [dimension], Elliptical galaxy, Spectral energy distribution, VERITAS, Astrophysics - High Energy Astrophysical Phenomena, Lorentz, Active galactic nucleus, Astrophysics::High Energy Astrophysical Phenomena, radio wave [galaxy], energy spectrum, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Cherenkov counter: atmosphere, VHE, GLAST, Telescope, X-ray, 0103 physical sciences, structure, Very Long Baseline Array, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, polarization, synchrotron radiation, background, galaxy: radio wave, Astronomy and Astrophysics, Doppler effect, flux, Crab Nebula, Space and Planetary Science, gamma ray, ddc:520, spectral, statistical
Abstract

The astrophysical journal 896(1), 41 - (2020). doi:10.3847/1538-4357/ab910e, The radio source 3C 264, hosted by the giant elliptical galaxy NGC 3862, was observed with VERITAS between February 2017 and May 2019. These deep observations resulted in the discovery of very-high-energy (VHE; E $>100$ GeV) $\gamma$-ray emission from this active galaxy. An analysis of $\sim$57 hours of quality-selected live time yields a detection at the position of the source, corresponding to a statistical significance of 7.8 standard deviations above background. The observed VHE flux is variable on monthly time scales, with an elevated flux seen in 2018 observations. The VHE emission during this elevated state is well-characterized by a power-law spectrum with a photon index $\Gamma = 2.20 \pm 0.27$ and flux F($>315$ GeV) = ($7.6\pm 1.2_{\mathrm stat} \pm 2.3_{\mathrm syst})\times 10^{-13}$ cm$^{-2}$ s$^{-1}$, or approximately 0.7% of the Crab Nebula flux above the same threshold. 3C 264 ($z = 0.0217$) is the most distant radio galaxy detected at VHE, and the elevated state is thought to be similar to that of the famously outbursting jet in M 87. Consequently, extensive contemporaneous multi-wavelength data were acquired in 2018 at the time of the VHE high state. An analysis of these data, including VLBA, VLA, HST, Chandra and Swift observations in addition to the VERITAS data, is presented, along with a discussion of the resulting spectral energy distribution., Published by Univ.8743, Chicago, Ill. [u.a.]

Published
2020
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9. Direct measurement of stellar angular diameters by the VERITAS Cherenkov telescopes

Author

M. J. Lang, Robert Brose, S. O'Brien, J. P. Finley, Gernot Maier, Nahee Park, T. J. Williamson, M. K. Daniel, Daniel Nieto, Jamie Holder, Wystan Benbow, A. M. Joyce, S. P. Wakely, John L. Quinn, Nolan Matthews, Cameron B Rulten, A. Petrashyk, D. S. Hanna, A. Furniss, T. B. Humensky, P. Kar, I. Sushch, R. M. Wells, P. Wilcox, P. Kaaret, N. Kelley-Hoskins, E. Roache, E. Pueschel, Ralph Bird, Martin Pohl, M. Kertzman, David Kieda, David A. Williams, Karlen Shahinyan, Tarek M. Hassan, I. Sadeh, R. A. Ong, C. Giuri, A. Brill, K. Ragan, Q. Feng, Gordon T. Richards, Maria Krause, Marcos Santander, M. Nievas-Rosillo, P. T. Reynolds, R. Mukherjee, T. T.Y. Lin, A. Wilhelm, P. Moriarty, Lucy Fortson, G. Hughes, G. H. Gillanders, Orel Gueta, A. J. Chromey, G. H. Sembroski, and Jules P. Halpern

Subjects
Brightness, 010504 meteorology & atmospheric sciences, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, 01 natural sciences, Occultation, law.invention, Telescope, Photometry (optics), Angular diameter, law, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, ddc:530, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), Astrophysics::Galaxy Astrophysics, Cherenkov radiation, 0105 earth and related environmental sciences, High Energy Astrophysical Phenomena (astro-ph.HE), Astroparticle physics, Physics, Astrophysics::Instrumentation and Methods for Astrophysics, Institut für Physik und Astronomie, Astronomy and Astrophysics, Stars, Astrophysics - Solar and Stellar Astrophysics, ddc:520, Astrophysics::Earth and Planetary Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract

Nature astronomy 3(6), 511 - 516 (2019). doi:10.1038/s41550-019-0741-z, The angular size of a star is a critical factor in determining its basic properties$^1$. Direct measurement of stellar angular diameters is difficult: at interstellar distances stars are generally too small to resolve by any individual imaging telescope. This fundamental limitation can be overcome by studying the diffraction pattern in the shadow cast when an asteroid occults a star$^2$, but only when the photometric uncertainty is smaller than the noise added by atmospheric scintillation$^3$. Atmospheric Cherenkov telescopes used for particle astrophysics observations have not generally been exploited for optical astronomy due to the modest optical quality of the mirror surface. However, their large mirror area makes them well suited for such high-time-resolution precision photometry measurements$^4$. Here we report two occultations of stars observed by the Very Energetic Radiation Imaging Telescope Array System (VERITAS)$^5$ Cherenkov telescopes with millisecond sampling, from which we are able to provide a direct measurement of the occulted stars’ angular diameter at the ≤0.1 mas scale. This is a resolution never achieved before with optical measurements and represents an order of magnitude improvement over the equivalent lunar occultation method$^6$. We compare the resulting stellar radius with empirically derived estimates from temperature and brightness measurements, confirming the latter can be biased for stars with ambiguous stellar classifications., Published by Nature Publishing Group, London

Published
2019
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10. Evidence for Proton Acceleration up to TeV Energies Based on VERITAS and Fermi-LAT Observations of the Cas A SNR

Author

Anushka Udara Abeysekara, M. J. Lang, A. Archer, K. Pfrang, P. Kaaret, O. Hervet, Gernot Maier, David A. Williams, Wystan Benbow, G. H. Gillanders, David Kieda, S. O'Brien, P. T. Reynolds, I. Sadeh, T. B. Humensky, Robert Brose, Frank Krennrich, A. J. Chromey, John L. Quinn, D. S. Hanna, P. Moriarty, James Buckley, Orel Gueta, Lucy Fortson, Augusto Ghiotto, Ralph Bird, N. Kelley-Hoskins, Q. Feng, P. Wilcox, A. Petrashyk, A. Gent, M. Kertzman, S. Das, E. Roache, E. Pueschel, M. Nievas-Rosillo, P. Kar, Vikram V. Dwarkadas, Martin Pohl, R. A. Ong, Karlen Shahinyan, Marcos Santander, Tarek M. Hassan, Reshmi Mukherjee, N. H. Park, A. Weinstein, C. Giuri, M. Buchovecky, Jamie Holder, Gordon T. Richards, G. H. Sembroski, A. D. Falcone, J. P. Finley, I. Sushch, G. Hughes, Weiguang Cui, Maria Krause, A. Wilhelm, S. Kumar, B. Zitzer, M. K. Daniel, T. J. Williamson, and K. Ragan

Subjects
High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Spectral index, Particle physics, 010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, Hadron, FOS: Physical sciences, Astronomy and Astrophysics, Context (language use), 01 natural sciences, Pion, Cover (topology), Space and Planetary Science, 0103 physical sciences, High Energy Physics::Experiment, Astrophysics - High Energy Astrophysical Phenomena, Supernova remnant, 010303 astronomy & astrophysics, Energy (signal processing), 0105 earth and related environmental sciences, Fermi Gamma-ray Space Telescope
Abstract

We present a study of $\gamma$-ray emission from the core-collapse supernova remnant Cas~A in the energy range from 0.1GeV to 10TeV. We used 65 hours of VERITAS data to cover 200 GeV - 10 TeV, and 10.8 years of \textit{Fermi}-LAT data to cover 0.1-500 GeV. The spectral analysis of \textit{Fermi}-LAT data shows a significant spectral curvature around $1.3 \pm 0.4_{stat}$ GeV that is consistent with the expected spectrum from pion decay. Above this energy, the joint spectrum from \textit{Fermi}-LAT and VERITAS deviates significantly from a simple power-law, and is best described by a power-law with spectral index of $2.17\pm 0.02_{stat}$ with a cut-off energy of $2.3 \pm 0.5_{stat}$ TeV. These results, along with radio, X-ray and $\gamma$-ray data, are interpreted in the context of leptonic and hadronic models. Assuming a one-zone model, we exclude a purely leptonic scenario and conclude that proton acceleration up to at least 6 TeV is required to explain the observed $\gamma$-ray spectrum. From modeling of the entire multi-wavelength spectrum, a minimum magnetic field inside the remnant of $B_{\mathrm{min}}\approx150\,\mathrm{\mu G}$ is deduced., Comment: 33 pages, 9 Figures, 6 Tables

Published
2020
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11. A Decade of Multiwavelength Observations of the TeV Blazar 1ES 1215+303: Extreme Shift of the Synchrotron Peak Frequency and Long-term Optical–Gamma-Ray Flux Increase

Author

Tuomas Savolainen, S. S. Scott, K. Nilsson, A. Wilhelm, Walter Max-Moerbeck, S. O'Brien, Alasdair E. Gent, Nahee Park, A. N. Otte, K. Ragan, R. A. Ong, G. H. Sembroski, K. Pfrang, Merja Tornikoski, T. J. Williamson, Wei Cui, Sebastian Kiehlmann, R. Shang, Marita Krause, Anushka Udara Abeysekara, Philip G. Edwards, Amy Furniss, P. Kaaret, A. Pichel, Gernot Maier, Alexander B. Pushkarev, D. Horan, Anne Lähteenmäki, Jamie Holder, V. V. Vassiliev, B. G. Piner, Lucy Fortson, A. Brill, P. Moriarty, Karlen Shahinyan, Tarek M. Hassan, Denis Bernard, J. H. Buckley, G. Hughes, M. Pohl, I. Sushch, M. Kertzman, A. C. S. Readhead, J. Valverde, Robert Brose, Wystan Benbow, Q. Feng, John L. Quinn, Daniel Nieto, Stephen Fegan, M. Nievas-Rosillo, D. Ribeiro, M. Buchovecky, Giuliana Noto, T. B. Humensky, Jenni Jormanainen, F. Krennrich, Talvikki Hovatta, M. J. Lang, A. Petrashyk, R. R. Prado, V. Fallah Ramazani, J. P. Finley, Jodi Christiansen, P. Wilcox, Olivier Hervet, A. J.R. Weinstein, A. D. Falcone, Matthew L. Lister, D. S. Hanna, N. Kelley-Hoskins, Ralph Bird, I. Sadeh, David A. Williams, Gordon T. Richards, A. Archer, E. Roache, D. B. Kieda, Orel Gueta, L. O. Takalo, G. H. Gillanders, Yuri Y. Kovalev, P. T. Reynolds, E. Lindfors, Marcos Santander, Reshmi Mukherjee, C. Giuri, R. M. Wells, E. Pueschel, Laboratoire Leprince-Ringuet (LLR), Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-École polytechnique (X)-Centre National de la Recherche Scientifique (CNRS), Fermi-LAT, VERITAS, Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3), University of Turku, Metsähovi Radio Observatory, Anne Lähteenmäki Group, Department of Electronics and Nanoengineering, Aalto-yliopisto, and Aalto University

Subjects
010504 meteorology & atmospheric sciences, Infrared, Flux, Astrophysics, 4/3, 01 natural sciences, law.invention, law, Jets, Broadband, 010303 astronomy & astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Gamma ray, Optical polarization, Galaxies: active, gamma-rays, Synchrotron, Wavelength, gamma ray: emission, optical [polarization], infrared, BL Lacertae objects, VERITAS, Astrophysics - High Energy Astrophysical Phenomena, Gamma-rays, ON 325, jets, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, GLAST, blazar, X-ray, emission [gamma ray], synchrotron, 0103 physical sciences, polarization: optical, Blazar, 0105 earth and related environmental sciences, B2 1215+30, S3 1215+30), Astronomy and Astrophysics, flux, 13. Climate action, Space and Planetary Science, correlation, Active galaxies, ddc:520, blazars BL Lacertae objects: individ- ual: 1ES 1215+303 (Ton 605, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Blazars
Abstract

Blazars are known for their variability on a wide range of timescales at all wavelengths. Most studies of TeV gamma-ray blazars focus on short timescales, especially during flares. With a decade of observations from the Fermi-LAT and VERITAS, we present an extensive study of the long-term multi-wavelength radio-to-gamma-ray flux-density variability, with the addition of a couple of short-time radio-structure and optical polarization observations of the blazar 1ES 1215+303 (z=0.130), with a focus on its gamma-ray emission from 100 MeV to 30 TeV. Multiple strong GeV gamma-ray flares, a long-term increase in the gamma-ray and optical flux baseline and a linear correlation between these two bands are observed over the ten-year period. Typical HBL behaviors are identified in the radio morphology and broadband spectrum of the source. Three stationary features in the innermost jet are resolved by VLBA at 43.1, 22.2, and 15.3 GHz. We employ a two-component synchrotron self-Compton model to describe different flux states of the source, including the epoch during which an extreme shift in energy of the synchrotron peak frequency from infrared to soft X-rays is observed., Comment: Accepted for publication in the Astrophysical Journal

Published
2020
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12. HESS J1943+213: An Extreme Blazar Shining through the Galactic Plane

Author

Amy Furniss, P. Pontrelli, Gordon T. Richards, A. Weinstein, Jamie Holder, A. N. Otte, M. Buchovecky, M. K. Daniel, Ralph Bird, Wystan Benbow, P. Kaaret, C. A. Johnson, Daniel Nieto, E. Pueschel, Maria Krause, I. Sadeh, O. M. Weiner, David Kieda, M. J. Lang, Wei Cui, R. A. Ong, Moritz Hütten, R. Mukherjee, Q. Feng, W. Brisken, P. T. Reynolds, Lucy Fortson, John L. Quinn, G. Hughes, Robert Brose, N. Kelley-Hoskins, D. S. Hanna, S. McArthur, T. T.Y. Lin, C. Rulten, V. Bugaev, A. Petrashyk, A. Flinders, P. Moriarty, O. Hervet, P. Kar, A. Popkow, P. Wilcox, E. Roache, A. Archer, R. M. Wells, Abraham D. Falcone, G. H. Sembroski, Karlen Shahinyan, David A. Williams, T. B. Humensky, G. H. Gillanders, M. Pohl, S. Kumar, J. P. Finley, S. P. Wakely, S. O'Brien, A. Wilhelm, N. H. Park, K. Ragan, J. Tyler, and F. Krennrich

Subjects
High Energy Astrophysical Phenomena (astro-ph.HE), Astroparticle physics, Physics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), European VLBI Network, 010308 nuclear & particles physics, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Galactic plane, 01 natural sciences, Redshift, Space and Planetary Science, 0103 physical sciences, Spectral energy distribution, ddc:520, Astrophysics - High Energy Astrophysical Phenomena, Blazar, 010303 astronomy & astrophysics, Very Long Baseline Array, Astrophysics::Galaxy Astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics, BL Lac object
Abstract

HESS J1943+213 is a very-high-energy (VHE; $>$100 GeV) $\gamma$-ray source in the direction of the Galactic Plane. Studies exploring the classification of the source are converging towards its identification as an extreme synchrotron BL Lac object. Here we present 38 hours of VERITAS observations of HESS J1943+213 taken over two years. The source is detected with $\sim$20 standard deviations significance, showing a remarkably stable flux and spectrum in VHE $\gamma$-rays. Multi-frequency very-long-baseline array (VLBA) observations of the source confirm the extended, jet-like structure previously found in the 1.6 GHz band with European VLBI Network and detect this component in the 4.6 GHz and the 7.3 GHz bands. The radio spectral indices of the core and the jet and the level of polarization derived from the VLBA observations are in a range typical for blazars. Data from VERITAS, $Fermi$-LAT, $Swift$-XRT, FLWO 48$''$ telescope, and archival infrared and hard X-ray observations are used to construct and model the spectral energy distribution (SED) of the source with a synchrotron-self-Compton model. The well-measured $\gamma$-ray peak of the SED with VERITAS and $Fermi$-LAT provides constraining upper limits on the source redshift. Possible contribution of secondary $\gamma$-rays from ultra-high-energy cosmic ray-initiated electromagnetic cascades to the $\gamma$-ray emission is explored, finding that only a segment of the VHE spectrum can be accommodated with this process. A variability search is performed across X-ray and $\gamma$-ray bands. No statistically significant flux or spectral variability is detected., Comment: Accepted for publication in The Astrophysical Journal

Published
2018
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13. Multiwavelength observations of the blazar BL Lacertae: a new fast TeV gamma-ray flare

Author

A. A. Mokrushina, J. P. Finley, B. Zitzer, A. N. Otte, M. P. Connolly, A. Weinstein, M. K. Daniel, Alan P. Marscher, C. A. Johnson, T. B. Humensky, N. H. Park, Robert Brose, Svetlana G. Jorstad, P. T. Reynolds, P. Kaaret, Anne Lähteenmäki, S. Enestam, R. A. Ong, Paul S. Smith, K. Ragan, Lucy Fortson, T. T.Y. Lin, P. Wilcox, Merja Tornikoski, T. Brantseg, Wystan Benbow, C. Rulten, Talvikki Hovatta, G. H. Gillanders, A. Petrashyk, P. Moriarty, S. P. Wakely, Martin Pohl, Yuri Y. Kovalev, M. Hütten, P. Kar, Marcos Santander, E. Pueschel, G. H. Sembroski, Q. Feng, I. Agudo, Wei Cui, Amy Furniss, Matthew L. Lister, José L. Gómez, M. Buchovecky, Gordon T. Richards, Tuomas Savolainen, Alexander B. Pushkarev, I. Gunawardhana, P. Pontrelli, I. Sadeh, J. H. Buckley, Sol N. Molina, R. Mukherjee, Anushka Udara Abeysekara, G. Hughes, S. O'Brien, G. A. Borman, D. S. Hanna, Sebastian Kiehlmann, R. M. Wells, Jamie Holder, V. Bugaev, M. J. Lang, Wara Chamani, Ralph Bird, Valeri M. Larionov, S. McArthur, O. Hervet, David A. Williams, E. Roache, Abraham D. Falcone, Karlen Shahinyan, John L. Quinn, M. Kertzman, Frank Krennrich, Department of Energy (US), National Science Foundation (US), Smithsonian Institution, National Research Council of Canada, National Aeronautics and Space Administration (US), Russian Foundation for Basic Research, Russian Government, Alexander von Humboldt Foundation, Academy of Finland, Ministerio de Economía y Competitividad (España), European Commission, Junta de Andalucía, and Russian Science Foundation

Subjects
jets, Active galactic nucleus, active [Galaxies], Astrophysics::High Energy Astrophysical Phenomena, galaxies: active, bl lacertae objects: individual (bl lacertae = ver j2202+422), FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, law.invention, law, emission, 0103 physical sciences, high-frequencies, Blazar, 010303 astronomy & astrophysics, Very Long Baseline Array, polarimetric observations, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Superluminal motion, variability, 010308 nuclear & particles physics, Astronomy and Astrophysics, Quasar, black-hole mass, lac objects, Crab Nebula, Space and Planetary Science, active galactic nuclei, ddc:520, radio polarization, Astrophysics - High Energy Astrophysical Phenomena, individual (BL Lacertae = VER J2202+422) [BL Lacertae objects], energy, Flare, Radio wave
Abstract

Combined with measurements made by very-long-baseline interferometry, the observations of fast TeV gamma-ray flares probe the structure and emission mechanism of blazar jets. However, only a handful of such flares have been detected to date, and only within the last few years have these flares been observed from lower-frequency-peaked BL Lac objects and flat-spectrum radio quasars. We report on a fast TeV gamma-ray flare from the blazar BL Lacertae observed by the Very Energetic Radiation Imaging Telescope Array System (VERITAS). with a rise time of ∼2.3 hr and a decay time of ∼36 min. The peak flux above 200 GeV is (4.2 ± 0.6) ×10 photon m s measured with a 4-minute-binned light curve, corresponding to ∼180% of the flux that is observed from the Crab Nebula above the same energy threshold. Variability contemporaneous with the TeV gamma-ray flare was observed in GeV gamma-ray, X-ray, and optical flux, as well as in optical and radio polarization. Additionally, a possible moving emission feature with superluminal apparent velocity was identified in Very Long Baseline Array observations at 43 GHz, potentially passing the radio core of the jet around the time of the gamma-ray flare. We discuss the constraints on the size, Lorentz factor, and location of the emitting region of the flare, and the interpretations with several theoretical models that invoke relativistic plasma passing stationary shocks.© 2018. The American Astronomical Society. All rights reserved., VERITAS is supported by grants from the U.S. Department of Energy Office of Science, the U.S. National Science Foundation and the Smithsonian Institution, and by NSERC in Canada. We acknowledge the excellent work of the technical support staff at the Fred Lawrence Whipple Observatory and at the collaborating institutions in the construction and operation of the instrument. The research at Boston University was supported in part by NASA Fermi Guest Investigator Program grant 80NSSC17K 0694. The VLBA is an instrument of the Long Baseline Observatory (LBO). The LBO is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. This research has made use of data from the MOJAVE database that is maintained by the MOJAVE team (Lister et al. 2009) and supported by NASA Fermi grant NNX15AU76G. This work made use of the Swinburne University of Technology software correlator (Deller et al. 2011), developed as part of the Australian Major National Research Facilities Programme and operated under licence. Y.Y.K. and A.B.P. are partly supported by the Russian Foundation for Basic Research (project 17-02-00197), the government of the Russian Federation (agreement 05.Y09.21.0018), and the Alexander von Humboldt Foundation. T.S. was funded by the Academy of Finland projects 274477 and 284495. This research has made use of data from the OVRO 40 m monitoring program (Richards et al. 2011) which is supported in part by NASA grants NNX08AW31G, NNX11A043G, and NNX14AQ89G and NSF grants AST-0808050 and AST-1109911. The monitoring of BL. Lacertae and other blazars at the Steward Observatory is supported through NASA Fermi Guest Investigator grant NNX15AU81G. I.A. acknowledges support by a Ramon y Cajal grant of the Ministerio de Economia y Competitividad (MINECO) of Spain. Acquisition and reduction of the MAPCAT data was supported in part by MINECO through grants AYA2010-14844, AYA2013-40825-P, and AYA2016-80889-P, and by the Regional Government of Andalucia through grant P09-FQM-4784. The MAPCAT observations were carried out at the German-Spanish Calar Alto Observatory, which is jointly operated by the Max-Planck-Institut fur Astronomie and the Instituto de Astrofisica de Andalucia-CSIC. The St. Petersburg University team acknowledges support from Russian Science Foundation grant 17-12-01029.

Published
2018
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14. Very-high-energy γ-ray observations of the blazar 1es 2344+514 with veritas

Author

A. Flinders, R. Mukherjee, P. Kaaret, E. Pueschel, A. McCann, D. S. Hanna, Martin Pohl, Maria Krause, Wei Cui, R. A. Ong, David Kieda, F. Krennrich, Daniel Nieto, M. K. Daniel, Wystan Benbow, A. N. Otte, Sinéad M. Griffin, M. P. Connolly, A. Wilhelm, A. Archer, Robert Brose, Moritz Hütten, Cameron H. Allen, J. Grube, C. Rulten, A. Petrashyk, G. H. Gillanders, Etienne Bourbeau, Lucy Fortson, N. H. Park, A. C. Rovero, P. Kar, P. T. Reynolds, N. Håkansson, Henrike Fleischhack, Gordon T. Richards, J. V. Tucci, Gernot Maier, M. Kertzman, A. O'Faolain de Bhroithe, J. Tyler, G. H. Sembroski, Matteo Cerruti, G. Hughes, J. H. Buckley, S. Archambault, M. Buchovecky, Amy Furniss, S. P. Wakely, S. O'Brien, I. Sadeh, A. Popkow, Marcos Santander, Thanh Huy Nguyen, J. V. Cardenzana, C. A. Johnson, K. Ragan, Jodi Christiansen, P. Moriarty, Xuhui Chen, M. Fernandez-Alonso, K. Meagher, Q. Feng, T. B. Humensky, J. P. Finley, John L. Quinn, S. Kumar, A. Pichel, E. Roache, Abraham D. Falcone, Karlen Shahinyan, Ralph Bird, S. McArthur, V. Bugaev, O. Hervet, J. D. Eisch, A. Weinstein, M. J. Lang, N. Kelley-Hoskins, I. Telezhinsky, Jamie Holder, and David A. Williams

Subjects
gamma-rays: galaxies, Point source, Ciencias Físicas, bl-lacertae objects, Astrophysics, telescope, 01 natural sciences, Spectral line, spectrum, purl.org/becyt/ford/1 [https], 0103 physical sciences, emission, ASTROPARTICLE PHYSICS, Blazar, 010303 astronomy & astrophysics, Physics, GALAXIES [GAMMA-RAYS], 010308 nuclear & particles physics, variability, Attenuation, Gamma ray, Astronomy, Institut für Physik und Astronomie, background-radiation, Astronomy and Astrophysics, purl.org/becyt/ford/1.3 [https], bl lacertae objects: individual: 1es 2344+514=verj2347+517, Light curve, Astronomía, radio, Extragalactic background light, x-ray, Space and Planetary Science, astroparticle physics, active galactic nuclei, ddc:520, BL LACERTAE OBJECTS, Astrophysics - High Energy Astrophysical Phenomena, constraints, CIENCIAS NATURALES Y EXACTAS, BL Lac object
Abstract

We present very-high-energy $\gamma$-ray observations of the BL Lac object 1ES 2344+514 taken by the Very Energetic Radiation Imaging Telescope Array System (VERITAS) between 2007 and 2015. 1ES 2344+514 is detected with a statistical significance above background of $20.8\sigma$ in $47.2$ hours (livetime) of observations, making this the most comprehensive very-high-energy study of 1ES 2344+514 to date. Using these observations the temporal properties of 1ES 2344+514 are studied on short and long times scales. We fit a constant flux model to nightly- and seasonally-binned light curves and apply a fractional variability test, to determine the stability of the source on different timescales. We reject the constant-flux model for the 2007-2008 and 2014-2015 nightly-binned light curves and for the long-term seasonally-binned light curve at the $> 3\sigma$ level. The spectra of the time-averaged emission before and after correction for attenuation by the extragalactic background light are obtained. The observed time-averaged spectrum above 200 GeV is satisfactorily fitted (${\chi^2/NDF = 7.89/6}$) by a power-law function with index $\Gamma = 2.46 \pm 0.06_{stat} \pm 0.20_{sys} $ and extends to at least 8 TeV. The extragalactic-background-light-deabsorbed spectrum is adequately fit (${\chi^2/NDF = 6.73/6}$) by a power-law function with index $\Gamma = 2.15 \pm 0.06_{stat} \pm 0.20_{sys} $ while an F-test indicates that the power-law with exponential cutoff function provides a marginally-better fit ($\chi^2/NDF $ = $2.56 / 5 $) at the 2.1$\sigma$ level. The source location is found to be consistent with the published radio location and its spatial extent is consistent with a point source., Comment: 7 pages, 2 figures. Published in Monthly Notices of the Royal Astronomical Society

Published
2017
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15. Gamma-ray Observations Under Bright Moonlight with VERITAS

Author

G. H. Gillanders, A. Weinstein, Martin Pohl, M. Kertzman, S. McArthur, Sinéad M. Griffin, Wystan Benbow, O. Hervet, P. Moriarty, Henrike Fleischhack, Q. Feng, A. Popkow, John L. Quinn, P. Kaaret, M. J. Lang, D. S. Hanna, David Kieda, Gordon T. Richards, Lucy Fortson, R. A. Ong, Ralph Bird, P. T. Reynolds, J. P. Finley, Wei Cui, J. V. Cardenzana, E. Pueschel, Maria Krause, David A. Williams, M. Buchovecky, C. A. Johnson, N. H. Park, Daniel Nieto, E. Roache, L. Ciupik, A. Bouvier, Gernot Maier, Abraham D. Falcone, M. K. Daniel, S. P. Wakely, A. N. Otte, Karlen Shahinyan, S. Archambault, S. O'Brien, K. Ragan, I. Telezhinsky, Jamie Holder, Matteo Cerruti, Amy Furniss, M. P. Connolly, G. Hughes, Etienne Bourbeau, B. Zitzer, A. Archer, T. T.Y. Lin, G. H. Sembroski, T. B. Humensky, Moritz Hütten, Manel Errando, I. Sadeh, R. Mukherjee, D. Staszak, S. Trepanier, P. Wilcox, V. Bugaev, C. Rulten, and P. Kar

Subjects
Moonlight, Astrophysics and Astronomy, Photomultiplier, Instrumentation, FOS: Physical sciences, IACT, Astrophysics, telescope, 01 natural sciences, law.invention, moon, iact, Positron, law, veritas, 0103 physical sciences, ddc:530, crab-nebula, 010303 astronomy & astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), Cherenkov radiation, Physics, instrumentation, 010308 nuclear & particles physics, Gamma ray, Institut für Physik und Astronomie, Astronomy and Astrophysics, moonlight, radiation, 13. Climate action, ddc:540, ddc:520, observing methods, Astrophysics - Instrumentation and Methods for Astrophysics, astro-ph.IM, Flare
Abstract

Astroparticle physics 91, 34 - 43 (2017). doi:10.1016/j.astropartphys.2017.03.001, Imaging atmospheric Cherenkov telescopes (IACTs) are equipped with sensitive photomultiplier tube (PMT) cameras. Exposure to high levels of background illumination degrades the efficiency of and potentially destroys these photo-detectors over time, so IACTs cannot be operated in the same configuration in the presence of bright moonlight as under dark skies. Since September 2012, observations have been carried out with the VERITAS IACTs under bright moonlight (defined as about three times the night-sky-background (NSB) of a dark extragalactic field, typically occurring when Moon illumination > 35%) in two observing modes, firstly by reducing the voltage applied to the PMTs and, secondly, with the addition of ultra-violet (UV) bandpass filters to the cameras. This has allowed observations at up to about 30 times previous NSB levels (around 80% Moon illumination), resulting in 30% more observing time between the two modes over the course of a year. These additional observations have already allowed for the detection of a flare from the 1ES 1727 + 502 and for an observing program targeting a measurement of the cosmic-ray positron fraction. We provide details of these new observing modes and their performance relative to the standard VERITAS observations., Published by Elsevier, Amsterdam [u.a.]

Published
2017
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16. Discovery of very high energy gamma rays from 1es 1440+122

Author

A. N. Otte, Geza Gyuk, E. Roache, M. P. Connolly, J. V. Tucci, Gernot Maier, S. P. Wakely, Abraham D. Falcone, Karlen Shahinyan, Wystan Benbow, N. Håkansson, Anna Barnacka, P. T. Reynolds, R. A. Ong, John L. Quinn, Ralph Bird, S. T. Griffiths, K. Sweeney, I. Telezhinsky, Jamie Holder, S. Federici, Martin Pohl, N. H. Park, J. Millis, J. Dumm, B. Zitzer, G. H. Sembroski, J. Grube, P. Kar, S. Godambe, Manel Errando, M. Kertzman, R. Welsing, M. J. Lang, L. C. Reyes, S. Kumar, K. Berger, Hugh Dickinson, D. S. Hanna, Xuhui Chen, Matteo Cerruti, Amy Furniss, Wei Cui, Henric Krawczynski, Y. Khassen, A. McCann, Q. Feng, A. O'Faolain de Bhroithe, David A. Williams, P. Kaaret, Lucy Fortson, D. Staszak, A. Popkow, Vladimir Vassiliev, H. Prokoph, Matthias Beilicke, J. S. Perkins, E. Pueschel, Markus Böttcher, J. Tyler, A. Wilhelm, A. Varlotta, A. Archer, J. V. Cardenzana, C. A. Johnson, E. Collins-Hughes, G. Hughes, David Kieda, Jodi Christiansen, J. D. Eisch, J. P. Finley, G. H. Gillanders, T. J. N. Nelson, S. McArthur, S. Griffin, K. Meagher, Jean-Francois Rajotte, S. Archambault, L. Ciupik, K. Ragan, V. Bugaev, H. Fleischhack, J. H. Buckley, A. W. Smith, A. S Madhavan, Gordon T. Richards, B. Behera, Daniel Nieto, and P. Moriarty

Subjects
extragalactic background light, multiwavelength observations, Astrophysics::High Energy Astrophysical Phenomena, bl-lacertae objects, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, bright blazars, 01 natural sciences, 7. Clean energy, law.invention, Telescope, law, 0103 physical sciences, intergalactic magnetic-field, Blazar, 010303 astronomy & astrophysics, Cherenkov radiation, Astrophysics::Galaxy Astrophysics, bl lacertae objects: general, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), 010308 nuclear & particles physics, tev blazars, Gamma ray, Astronomy, Institut für Physik und Astronomie, Astronomy and Astrophysics, source catalog, gamma-rays: general, Redshift, large-area telescope, einstein slew survey, Crab Nebula, 13. Climate action, Space and Planetary Science, active galactic nuclei, ddc:520, High Energy Physics::Experiment, Astrophysics - High Energy Astrophysical Phenomena, BL Lac object, Fermi Gamma-ray Space Telescope
Abstract

The BL Lacertae object 1ES 1440+122 was observed in the energy range from 85 GeV to 30 TeV by the VERITAS array of imaging atmospheric Cherenkov telescopes. The observations, taken between 2008 May and 2010 June and totalling 53 hours, resulted in the discovery of $\gamma$-ray emission from the blazar, which has a redshift $z$=0.163. 1ES 1440+122 is detected at a statistical significance of 5.5 standard deviations above the background with an integral flux of (2.8$\pm0.7_{\mathrm{stat}}\pm0.8_{\mathrm{sys}}$) $\times$ 10$^{-12}$ cm$^{-2}$ s$^{-1}$ (1.2\% of the Crab Nebula's flux) above 200 GeV. The measured spectrum is described well by a power law from 0.2 TeV to 1.3 TeV with a photon index of 3.1 $\pm$ 0.4$_{\mathrm{stat}}$ $\pm$ 0.2$_{\mathrm{sys}}$. Quasi-simultaneous multi-wavelength data from the Fermi Large Area Telescope (0.3--300 GeV) and the Swift X-ray Telescope (0.2--10 keV) are additionally used to model the properties of the emission region. A synchrotron self-Compton model produces a good representation of the multi-wavelength data. Adding an external-Compton or a hadronic component also adequately describes the data., Comment: 8 pages, 4 figures. Accepted for publication in MNRAS

Published
2016
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17. A search for brief optical flashes associated with the seti target kic 8462852

Author

M. Buchovecky, Q. Feng, J. Grube, I. Telezhinsky, Jamie Holder, S. O'Brien, P. T. Reynolds, A. McCann, P. Fortin, Ralph Bird, Hugh Dickinson, Wystan Benbow, Anushka Udara Abeysekara, S. Archambault, Reshmi Mukherjee, A. Archer, D. Staszak, Martin Pohl, A. N. Otte, K. Meagher, S. McArthur, E. Pueschel, Maria Krause, O. M. Weiner, D. J. Fegan, Karen Byrum, J. D. Eisch, Abraham D. Falcone, Daniel Nieto, A. Weinstein, Karlen Shahinyan, S. Vincent, G. H. Gillanders, N. H. Park, D. S. Hanna, L. Ciupik, David A. Williams, N. Håkansson, Henrike Fleischhack, P. Kaaret, J. V. Cardenzana, J. V. Tucci, M. J. Lang, Moritz Hütten, Gernot Maier, John L. Quinn, N. Kelley-Hoskins, C. A. Johnson, K. Ragan, Geza Gyuk, Lucy Fortson, S. P. Wakely, R. A. Ong, David Kieda, F. Krennrich, Sinéad M. Griffin, J. Tyler, Matteo Cerruti, J. H. Buckley, Amy Furniss, Gordon T. Richards, E. Roache, P. Moriarty, J. P. Finley, G. Ratliff, Xuhui Chen, J. S. Perkins, Jodi Christiansen, T. B. Humensky, G. H. Sembroski, B. Zitzer, Manel Errando, S. Kumar, T. T.Y. Lin, A. Popkow, M. Kertzman, A. O'Faolain de Bhroithe, Wei Cui, A. Petrashyk, P. Kar, Marcos Santander, and ~

Subjects
stars, Photon, spectra, Astrophysics::High Energy Astrophysical Phenomena, astrobiology, FOS: Physical sciences, system, 01 natural sciences, oseti, extraterrestrial intelligence, law.invention, Telescope, Physics::Popular Physics, techniques: photometric, Observatory, law, veritas, 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, Pulse intensity, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), Cherenkov radiation, Search for extraterrestrial intelligence, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, 010308 nuclear & particles physics, bursts, Extraterrestrial intelligence, Astrophysics::Instrumentation and Methods for Astrophysics, Institut für Physik und Astronomie, Astronomy, Astronomy and Astrophysics, telescopes, stars: individual ( kic 8462852), Stars, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, ddc:520, Astrophysics::Earth and Planetary Astrophysics, methods: observational, Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Abstract

The astrophysical journal / 2 818(2), L33(2016). doi:10.3847/2041-8205/818/2/L33, The F-type star KIC 8462852 has recently been identified as an exceptional target for search for extraterrestrial intelligence (SETI) observations. We describe an analysis methodology for optical SETI, which we have used to analyze nine hours of serendipitous archival observations of KIC 8462852 made with the VERITAS gamma-ray observatory between 2009 and 2015. No evidence of pulsed optical beacons, above a pulse intensity at the Earth of approximately $1\;\mathrm{photon}\;{{\rm{m}}}^{-2}$, is found. We also discuss the potential use of imaging atmospheric Cherenkov telescope arrays in searching for extremely short duration optical transients in general., Published by Institute of Physics Publ., London

Published
2016
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18. A search for very high energy gamma rays from the missing link binary pulsar J1023+0038 with VERITAS

Author

Wystan Benbow, John L. Quinn, A. Petrashyk, M. J. Lang, P. Kar, O. M. Weiner, Jonathan Biteau, J. P. Finley, B. Zitzer, N. Håkansson, Henrike Fleischhack, David Kieda, A. W. Smith, A. Flinders, Q. Feng, Abraham D. Falcone, Gordon T. Richards, E. Roache, Karlen Shahinyan, E. Pueschel, Geza Gyuk, S. Vincent, Nahee Park, A. Varlotta, N. Kelley-Hoskins, T. B. Humensky, Maria Krause, P. Moriarty, K. L. Byrum, Wei Cui, J. Grube, P. Kaaret, J. V. Cardenzana, J. D. Eisch, S. McArthur, A. McCann, Xuhui Chen, V. Bugaev, L. Ciupik, S. Archambault, Reshmi Mukherjee, Daniel Nieto, A. O'Faolain de Bhroithe, Sinéad M. Griffin, A. Popkow, E. Aliu, Maria Chernyakova, Lucy Fortson, J. Tyler, Matteo Cerruti, Moritz Hütten, J. H. Buckley, R. A. Ong, A. N. Otte, Amy Furniss, Marcos Santander, M. Kertzman, Martin Pohl, S. P. Wakely, P. Fortin, V. Pelassa, C. B. Rulten, Ralph Bird, G. H. Sembroski, A. Loo, K. Meagher, Hugh Dickinson, Mallory S. E. Roberts, M. Buchovecky, M. P. Connolly, D. Pandel, P. T. Reynolds, A. J.R. Weinstein, C. A. Johnson, J. V. Tucci, Gernot Maier, A. Wilhelm, D. Staszak, K. Ragan, I. Telezhinsky, Jamie Holder, David A. Williams, Thanh Huy Nguyen, A. Archer, and G. H. Gillanders

Subjects
nustar observations, Astrophysics::High Energy Astrophysical Phenomena, Flux, Binary number, FOS: Physical sciences, Astrophysics, telescope, 01 natural sciences, Binary pulsar, Pulsar, pulsars: general, psr j1023+0038, emission, 0103 physical sciences, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Millisecond, state change, 010308 nuclear & particles physics, pulsars: individual (psr j1023+0038), periastron, Gamma ray, transition, Institut für Physik und Astronomie, Astronomy and Astrophysics, gamma rays: general, 1st j102347.6+003841, Magnetic field, Neutron star, binaries: general, 13. Climate action, Space and Planetary Science, ddc:520, Astrophysics - High Energy Astrophysical Phenomena, millisecond pulsar, discovery
Abstract

The binary millisecond radio pulsar PSR J1023+0038 exhibits many characteristics similar to the gamma-ray binary system PSR B1259--63/LS 2883, making it an ideal candidate for the study of high-energy non-thermal emission. It has been the subject of multi-wavelength campaigns following the disappearance of the pulsed radio emission in 2013 June, which revealed the appearance of an accretion disk around the neutron star. We present the results of very high-energy gamma-ray observations carried out by VERITAS before and after this change of state. Searches for steady and pulsed emission of both data sets yield no significant gamma-ray signal above 100 GeV, and upper limits are given for both a steady and pulsed gamma-ray flux. These upper limits are used to constrain the magnetic field strength in the shock region of the PSR J1023+0038 system. Assuming that very high-energy gamma rays are produced via an inverse-Compton mechanism in the shock region, we constrain the shock magnetic field to be greater than $\sim$2 G before the disappearance of the radio pulsar and greater than $\sim$10 G afterwards., 7 pages, 3 figures, accepted for publication in ApJ

Published
2016
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19. Multiband variability studies and novel broadband SED modeling of Mrk 501 in 2009

Author

K. Nishijima, J. L. Richards, Stefano Covino, G. Piner, D. Dominis Prester, U. Menzel, A. Flinders, D. Tescaro, Louis Antonelli, D. Galindo, Aaron Dominguez, S. Schröder, Elena G. Larionova, Kari Nilsson, Paul S. Smith, A. McCann, T. S. Grishina, Wen Ping Chen, M. Will, Pratik Majumdar, J. E. Ward, Daniela Dorner, Dariusz Gora, P. Moriarty, C. Rulten, Soebur Razzaque, D. Garrido Terrats, K. Frantzen, Joseph Moody, Wystan Benbow, G. Hughes, K. Ragan, Ralph Bird, L. Perri, M. Gaug, T. Sakamoto, Valeri M. Larionov, Elina Lindfors, G. H. Sembroski, Daniel Mazin, Ievgen Vovk, A. Hahn, M. Hütten, N. H. Park, Alexander B. Pushkarev, G. Maccaferri, Thomas Bretz, P. Wilcox, P. Kar, D. Nakajima, R. Zanin, J. Herrera, Wei Cui, Amanda Weinstein, J. Palacio, P. G. Prada Moroni, Frank Krennrich, Matthew L. Lister, A. Berti, A. Cesarini, M. Kertzman, A. La Barbera, Walter Max-Moerbeck, E. Colombo, M. Villata, M. P. Connolly, Adrian Biland, D. S. Hanna, Ana Babić, D. Eisenacher Glawion, Juan Abel Barrio, John L. Quinn, M. Capalbi, Koji Noda, Arka Chatterjee, Elisa Bernardini, A. Sillanpää, Adrian Rovero, Antonio Stamerra, J. V. Tucci, M. Nievas Rosillo, M. Palatiello, L. V. Larionova, S. N. Shore, R. Mukherjee, M. J. Lang, Daniel Nieto, M. I. Martínez, S. Bonnefoy, J. Kushida, P. Giammaria, P. Bangale, Wolfgang Rhode, Gernot Maier, G. Pedaletti, L. O. Takalo, Margo F. Aller, Jose Luis Contreras, Andrei Berdyugin, J. A. Zensus, E. Roache, V. Verguilov, D. Fidalgo, C. Pace, Thomas P. Krichbaum, Francesco Dazzi, Juan Cortina, M. Engelkemeier, G. H. Gillanders, A. Carraminyana, S. P. Wakely, Mosè Mariotti, J. Rico, A. Fernández-Barral, R. Clavero, J. Becerra González, A.-K. Overkemping, S. O. Kurtanidze, Sabrina Einecke, Abraham D. Falcone, A. González Muñoz, Evgenia N. Kopatskaya, Lars Fuhrmann, Nikola Godinovic, Benito Marcote, Karlen Shahinyan, Takashi Saito, W. Bednarek, C. Schultz, Marcos Santander, Fabrizio Tavecchio, J. Rodriguez Garcia, E. Pueschel, Ll. Font, A. C. Sadun, A. Popkow, J. Grube, V. Bugaev, Anthony C. S. Readhead, R. Ligustri, A. Archer, I. Snidaric, Yusuke Konno, P. Calcidese, M. Strzys, A. Pichel, Saverio Lombardi, B. De Lotto, Markus Garczarczyk, N. Kelley-Hoskins, J. Tyler, Ann E. Wehrle, B. Banerjee, S. Buson, D. Hadasch, N. Otte, Maria G. Nikolashvili, Gordon T. Richards, L. Nogués, B. Biasuzzi, Juri Poutanen, U. Barres de Almeida, J. P. Finley, K. Mallot, S. Paiano, Marcello Giroletti, I. Nestoras, A. De Angelis, A. Treves, Vitaly Neustroev, X. Paredes-Fortuny, T. B. Humensky, R. A. Ong, Karl Mannheim, J. H. Buckley, Yu. A. Kovalev, R. J. García López, H. Fleischhack, G. N. Kimeridze, I. Sadeh, David A. Williams, Y. Mori, M. V. Fonseca, W. Idec, Matthias Kadler, Yuri Y. Kovalev, Stefano Ansoldi, Riccardo Paoletti, K. Kodani, J. P. Norris, O. M. Kurtanidze, N. V. Efimova, Y. Hanabata, Arkady A. Arkharov, Anne Lähteenmäki, Abelardo Moralejo, G. Maneva, Masahiro Teshima, A. C. Zook, Dario Hrupec, P. Antoranz, B. Zitzer, Hugh Dickinson, R. A. Chigladze, M. Peresano, Ekaterina Koptelova, S. Archambault, M. A. Lopez, T. Steinbring, P. Temnikov, P. Leto, Massimo Persic, J. M. Paredes, Hugh D. Aller, F. Borracci, S. O'Brien, T. Surić, I. Telezhinsky, I. Reichardt, Jamie Holder, G. Vanzo, R. Pearson, Julia Thaele, G. Bonnoli, Mark Gurwell, Eduardo Ros, Andrea Orlati, S. Griffin, L. A. Sigua, Diego F. Torres, Alessandro Carosi, Ruben Lopez-Coto, Maria Krause, Y. Yatsu, A. Wilhelm, Jose Miguel Miranda, Anushka Udara Abeysekara, T. Schweizer, P. Cassaro, Razmik Mirzoyan, E. Moretti, Damir Lelas, Francesco Longo, V. Fallah Ramazani, P. Kaaret, Dorota Sobczyńska, L. Maraschi, Kirill Sokolovsky, Tomislav Terzić, Lucy Fortson, E. de Ona Wilhelmi, Julian Sitarek, C. Fruck, T. Toyama, Ivica Puljak, Max Ludwig Ahnen, David Kieda, F. Di Pierro, Pierre Colin, M. Buchovecky, Oscar Blanch, P. Da Vela, A. Niedzwiecki, Emmanouil Angelakis, M. Doert, M. H. Wu, Ivan S. Troitsky, C. Pagani, David Paneque, Q. Feng, Vladimir A. Hagen-Thorn, E. De la Fuente, E. Prandini, C. M. Raiteri, L. Carrasco, D. Guberman, Jeremy S. Perkins, Martin Pohl, Marina Manganaro, H. A. Krimm, Merja Tornikoski, Konstancja Satalecka, Michele Doro, Dmitry A. Blinov, M. Perri, J. Hose, D. Elsaesser, Daria A. Morozova, P. T. Reynolds, M. Hayashida, Marc Ribó, Hidetoshi Kubo, M. Makariev, Swiss Federal Institute of Technology Zurich, University of Udine, INAF National Institute for Astrophysics, University of Siena, University of Rijeka, Saha Institute of Nuclear Physics, Max Planck Institute for Physics, Complutense University, University of La Laguna, University of Łódź, German Electron Synchrotron, Autonomous University of Barcelona, University of Würzburg, University of Padova, Institute of Space Studies of Catalonia, Dortmund University, Finnish MAGIC Consortium, University of Barcelona, The University of Tokyo, Bulgarian Academy of Sciences, Osservatorio Astronomicodi Roma, University of Pisa, ICREA, University of Maryland, College Park, McGill University, Washington University St. Louis, Harvard University, University College Dublin, University of California Los Angeles, National University of Ireland, Galway, Purdue University, Iowa State University, Pennsylvania State University, University of Utah, University of Minnesota Twin Cities, Adler Planetarium and Astronomy Museum, University of Delaware, Columbia University, University of Iowa, DePauw University, Georgia Institute of Technology, University of Chicago, NASA Goddard Space Flight Center, Universidad de Buenos Aires, Cork Institute of Technology, University of California Santa Cruz, Argonne National Laboratory, University of Johannesburg, University of Michigan, Ann Arbor, St. Petersburg State University, RAS - Pulkovo Astronomical Observatory, Circolo Astrofili Talmassons, Osservatorio Astrofisico della Regione Autonoma Valle d'Aosta, Georgian National Academy of Sciences, National Central University, Aoyama Gakuin University, University of Colorado Denver, Brigham Young University, Tokyo Institute of Technology, Instituto Nacional de Astrofisica Optica y Electronica, Universidad de Guadalajara, University of Denver, University of Arizona, Space Science Institute, Pomona College, University of Leicester, ASI Science Data Center, University of Trento, RAS - P.N. Lebedev Physics Institute, Max Planck Institute for Radio Astronomy, Whittier College, Metsähovi Radio Observatory, INAF Istituto di Radioastronomia, Osservatorio Astrofisico di Catania, California Institute of Technology, Department of Electronics and Nanoengineering, Aalto-yliopisto, Aalto University, Ahnen, M. L., Ansoldi, S., Antonelli, L. A., Antoranz, P., Babic, A., Banerjee, B., Bangale, P., Barres De Almeida, U., Barrio, J. A., Becerra González, J., Bednarek, W., Bernardini, E., Berti, Alessio, Biasuzzi, B., Biland, A., Blanch, O., Bonnefoy, S., Bonnoli, G., Borracci, F., Bretz, T., Buson, S., Carosi, A., Chatterjee, A., Clavero, R., Colin, P., Colombo, E., Contreras, J. L., Cortina, J., Covino, S., Da Vela, P., Dazzi, F., De Angelis, A., De Lotto, B., De Oña Wilhelmi, E., Di Pierro, F., Doert, M., Domã­nguez, A., Dominis Prester, D., Dorner, D., Doro, M., Einecke, S., Eisenacher Glawion, D., Elsaesser, D., Engelkemeier, M., Fallah Ramazani, V., Fernández Barral, A., Fidalgo, D., Fonseca, M. V., Font, L., Frantzen, K., Fruck, C., Galindo, D., García López, R. J., Garczarczyk, M., Garrido Terrats, D., Gaug, M., Giammaria, P., Godinoviä , N., González Muñoz, A., Gora, D., Guberman, D., Hadasch, D., Hahn, A., Hanabata, Y., Hayashida, M., Herrera, J., Hose, J., Hrupec, D., Hughes, G., Idec, W., Kodani, K., Konno, Y., Kubo, H., Kushida, J., La Barbera, A., Lelas, D., Lindfors, E., Lombardi, S., Longo, Francesco, Lã³pez, M., López Coto, R., Majumdar, P., Makariev, M., Mallot, K., Maneva, G., Manganaro, M., Mannheim, K., Maraschi, L., Marcote, B., Mariotti, M., Martã­nez, M., Mazin, D., Menzel, U., Miranda, J. M., Mirzoyan, R., Moralejo, A., Moretti, E., Nakajima, D., Neustroev, V., Niedzwiecki, A., Nievas Rosillo, M., Nilsson, K., Nishijima, K., Noda, K., Noguã©s, L., Overkemping, A., Paiano, S., Palacio, J., Palatiello, Michele, Paneque, D., Paoletti, R., Paredes, J. M., Paredes Fortuny, X., Pedaletti, G., Peresano, M., Perri, L., Persic, M., Poutanen, J., Prada Moroni, P. G., Prandini, E., Puljak, I., Reichardt, I., Rhode, W., Ribã³, M., Rico, J., Rodriguez Garcia, J., Saito, T., Satalecka, K., Schrã¶der, S., Schultz, C., Schweizer, T., Shore, S. N., Sillanpã¤ã¤, A., Sitarek, J., Snidaric, I., Sobczynska, D., Stamerra, A., Steinbring, T., Strzys, M., Suriä , T., Takalo, L., Tavecchio, F., Temnikov, P., Terziä , T., Tescaro, D., Teshima, M., Thaele, J., Torres, D. F., Toyama, T., Treves, A., Vanzo, G., Verguilov, V., Vovk, I., Ward, J. E., Will, M., Wu, M. H., Zanin, R., Abeysekara, A. U., Archambault, S., Archer, A., Benbow, W., Bird, R., Buchovecky, M., Buckley, J. H., Bugaev, V., Connolly, M. P., Cui, W., Dickinson, H. J., Falcone, A., Feng, Q., Finley, J. P., Fleischhack, H., Flinders, A., Fortson, L., Gillanders, G. H., Griffin, S., Grube, J., Hã¼tten, M., Hanna, D., Holder, J., Humensky, T. B., Kaaret, P., Kar, P., Kelley Hoskins, N., Kertzman, M., Kieda, D., Krause, M., Krennrich, F., Lang, M. J., Maier, G., Mccann, A., Moriarty, P., Mukherjee, R., Nieto, D., O'Brien, S., Ong, R. A., Otte, N., Park, N., Perkins, J., Pichel, A., Pohl, M., Popkow, A., Pueschel, E., Quinn, J., Ragan, K., Reynolds, P. T., Richards, G. T., Roache, E., Rovero, A. C., Rulten, C., Sadeh, I., Santander, M., Sembroski, G. H., Shahinyan, K., Telezhinsky, I., Tucci, J. V., Tyler, J., Wakely, S. P., Weinstein, A., Wilcox, P., Wilhelm, A., Williams, D. A., Zitzer, B., Razzaque, S., Villata, M., Raiteri, C. M., Aller, H. D., Aller, M. F., Larionov, V. M., Arkharov, A. A., Blinov, D. A., Efimova, N. V., Grishina, T. S., Hagen Thorn, V. A., Kopatskaya, E. N., Larionova, L. V., Larionova, E. G., Morozova, D. A., Troitsky, I. S., Ligustri, R., Calcidese, P., Berdyugin, A., Kurtanidze, O. M., Nikolashvili, M. G., Kimeridze, G. N., Sigua, L. A., Kurtanidze, S. O., Chigladze, R. A., Chen, W. P., Koptelova, E., Sakamoto, T., Sadun, A. C., Moody, J. W., Pace, C., Pearson, R., Yatsu, Y., Mori, Y., Carraminyana, A., Carrasco, L., De La Fuente, E., Norris, J. P., Smith, P. S., Wehrle, A., Gurwell, M. A., Zook, A., Pagani, C., Perri, M., Capalbi, M., Cesarini, A., Krimm, H. A., Kovalev, Y. Y., Kovalev, Y. u. A., Ros, E., Pushkarev, A. B., Lister, M. L., Sokolovsky, K. V., Kadler, M., Piner, G., Lã¤hteenmã¤ki, A., Tornikoski, M., Angelakis, E., Krichbaum, T. P., Nestoras, I., Fuhrmann, L., Zensus, J. A., Cassaro, P., Orlati, A., Maccaferri, G., Leto, P., Giroletti, M., Richards, J. L., Max Moerbeck, W., and Readhead, A. C. S.

Subjects
extragalactic background light, multiwavelength observations, Astrophysics::High Energy Astrophysical Phenomena, bl-lacertae objects, Galaxies: BL Lacertae objects: individual: Markarian 501, Methods: data analysis, observational, Polarization, spectral energy-distribution, Flux, FOS: Physical sciences, Astrophysics, 01 natural sciences, law.invention, individual: Markarian 501 [BL Lacertae objects], law, Coincident, 0103 physical sciences, ddc:530, MAGIC (telescope), crab-nebula, Blazar, data analysis [Methods], 010303 astronomy & astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), tev blazars, 010308 nuclear & particles physics, stochastic acceleration, telescope observations, Institut für Physik und Astronomie, Astronomy and Astrophysics, Astronomy and Astrophysic, gamma-ray emission, methods: data analysis, BL Lacertae objects: individual: Markarian 501, Synchrotron, data analysi [Methods], Space and Planetary Science, x-ray, ddc:520, Electrónica, Física nuclear, Electricidad, Degeneracy (mathematics), Astrophysics - High Energy Astrophysical Phenomena, Flare, BL Lac object
Abstract

Astronomy and astrophysics 603, A31 (2017). doi:10.1051/0004-6361/201629540, We present an extensive study of the BL Lac object Mrk 501 based on a data set collected during the multi-instrument campaign spanning from 2009 March 15 to 2009 August 1, which includes, among other instruments, MAGIC, VERITAS, Whipple 10 m, and Fermi-LAT to cover the γ-ray range from 0.1 GeV to 20 TeV; RXTE and Swift to cover wavelengths from UV tohard X-rays; and GASP-WEBT, which provides coverage of radio and optical wavelengths. Optical polarization measurements were provided for a fraction of the campaign by the Steward and St. Petersburg observatories. We evaluate the variability of the source and interband correlations, the γ-ray flaring activity occurring in May 2009, and interpret the results within two synchrotron self-Compton (SSC) scenarios. Aims. The multiband variability observed during the full campaign is addressed in terms of the fractional variability, and the possible correlations are studied by calculating the discrete correlation function for each pair of energy bands where the significance was evaluated with dedicated Monte Carlo simulations. The space of SSC model parameters is probed following a dedicated grid-scan strategy, allowing for a wide range of models to be tested and offering a study of the degeneracy of model-to-data agreement in the individual model parameters, hence providing a less biased interpretation than the “single-curve SSC model adjustment” typically reported in the literature. Methods. We find an increase in the fractional variability with energy, while no significant interband correlations of flux changes are found on the basis of the acquired data set. The SSC model grid-scan shows that the flaring activity around May 22 cannot be modeled adequately with a one-zone SSC scenario (using an electron energy distribution with two breaks), while it can be suitably described within a two (independent) zone SSC scenario. Here, one zone is responsible for the quiescent emission from the averaged 4.5-month observing period, while the other one, which is spatially separated from the first, dominates the flaring emission occurring at X-rays and very-high-energy (>100 GeV, VHE) γ rays. The flaring activity from May 1, which coincides with a rotation of the electric vector polarization angle (EVPA), cannot be satisfactorily reproduced by either a one-zone or a two-independent-zone SSC model, yet this is partially affected by the lack of strictly simultaneous observations and the presence of large flux changes on sub-hour timescales (detected at VHE γ rays). Results. The higher variability in the VHE emission and lack of correlation with the X-ray emission indicate that, at least during the 4.5-month observing campaign in 2009, the highest energy (and most variable) electrons that are responsible for the VHE γ rays do not make a dominant contribution to the ~1 keV emission. Alternatively, there could be a very variable component contributing to the VHE γ-ray emission in addition to that coming from the SSC scenario. The studies with our dedicated SSC grid-scan show that there is some degeneracy in both the one-zone and the two-zone SSC scenarios probed, with several combinations of model parameters yielding a similar model-to-data agreement, and some parameters better constrained than others. The observed γ-ray flaring activity, with the EVPA rotation coincident with the first γ-ray flare, resembles those reported previously for low frequency peaked blazars, hence suggesting that there are many similarities in the flaring mechanisms of blazars with different jet properties., Published by EDP Sciences, Les Ulis

Published
2016
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20. VERITAS and multiwavelength observations of the BL Lacertae object 1ES 1741+196

Author

J. V. Cardenzana, J. Biteau, C. A. Johnson, A. McCann, N. Kelley-Hoskins, K. Reynolds, R. A. Ong, Sinéad M. Griffin, D. Petry, D. S. Hanna, A. N. Otte, M. P. Connolly, Lucy Fortson, P. Kaaret, S. McArthur, V. Bugaev, J. Tyler, E. Roache, J. P. Finley, David Kieda, J. H. Buckley, B. Zitzer, A. Archer, F. Krennrich, G. H. Gillanders, J. Grube, G. Ratliff, Wystan Benbow, Manel Errando, A. Flinders, M. J. Lang, Xuhui Chen, Q. Feng, Abraham D. Falcone, Karlen Shahinyan, A. Popkow, E. Pueschel, Maria Krause, M. Huetten, O. M. Weiner, M. Kertzman, M. Buchovecky, A. O'Faolain de Bhroithe, Karen Byrum, J. D. Eisch, A. Weinstein, K. Meagher, Henrike Fleischhack, A. W. Smith, T. B. Humensky, S. Archambault, Martin Pohl, Gordon T. Richards, Geza Gyuk, P. Fortin, Marcos Santander, J. Dumm, Ralph Bird, Jodi Christiansen, John L. Quinn, P. T. Reynolds, C. B. Rulten, Matteo Cerruti, Amy Furniss, P. Moriarty, Daniel Nieto, L. Ciupik, K. Ragan, A. Wilhelm, S. Vincent, Hugh Dickinson, N. H. Park, S. O'Brien, J. V. Tucci, Gernot Maier, S. P. Wakely, R. Mukherjee, Anushka Udara Abeysekara, V. Pelassa, A. Petrashyk, P. Kar, G. H. Sembroski, David A. Williams, D. Staszak, I. Telezhinsky, Jamie Holder, L. C. Reyes, and Wei Cui

Subjects
Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Flux, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, telescope, 01 natural sciences, law.invention, Telescope, swift, law, gamma-ray astronomy, 0103 physical sciences, Blazar, 010303 astronomy & astrophysics, relativistic processes, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Spectral index, 010308 nuclear & particles physics, tev blazars, Institut für Physik und Astronomie, Astronomy, Astronomy and Astrophysics, Gamma-ray astronomy, source catalog, lac objects, spectral energy-distributions, Crab Nebula, x-ray, Space and Planetary Science, astroparticle physics, Spectral energy distribution, ddc:520, High Energy Physics::Experiment, Astrophysics - High Energy Astrophysical Phenomena, fermi, galaxies: individual: 1es 1741+196=ver j1744+195, discovery, BL Lac object
Abstract

Monthly notices of the Royal Astronomical Society 459(3), 2550 - 2557 (2016). doi:10.1093/mnras/stw664, We present results from multiwavelength observations of the BL Lacertae object 1ES 1741 + 196, including results in the very high energy γ-ray regime using the Very Energetic Radiation Imaging Telescope Array System (VERITAS). The VERITAS time-averaged spectrum, measured above 180 GeV, is well modelled by a power law with a spectral index of 2.7 ± 0.7$_{stat}$ ± 0.2syst. The integral flux above 180 GeV is (3.9 ± 0.8$_{stat}$ ± 1.0$_{syst}$) × 10$^{−8}$ m$^{−2}$ s$^{−1}$, corresponding to 1.6 per cent of the Crab nebula flux on average. The multiwavelength spectral energy distribution of the source suggests that 1ES 1741+196 is an extreme-high-frequency-peaked BL Lacertae object. The observations analysed in this paper extend over a period of six years, during which time no strong flares were observed in any band. This analysis is therefore one of the few characterizations of a blazar in a non-flaring state., Published by Oxford Univ. Press, Oxford

Published
2016
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21. TeV Gamma-ray Observations of The Galactic Center Ridge By VERITAS

Author

Julien Rousselle, V. V. Vassiliev, J. V. Tucci, A. Furniss, Avery Archer, S. P. Wakely, T. B. Humensky, M. J. Lang, Maria Krause, Wystan Benbow, A. Popkow, J. Tyler, P. Kaaret, K. Ragan, Lucy Fortson, A. Flinders, J. H. Buckley, B. Zitzer, M. Kertzman, John L. Quinn, N. Håkansson, S. McArthur, Martin Pohl, Marcos Santander, E. Roache, P. T. Reynolds, Matteo Cerruti, Geza Gyuk, J. V. Cardenzana, D. A. Williams, K. Meagher, G. Ratliff, S. Griffin, Abraham D. Falcone, Karlen Shahinyan, C. A. Johnson, H. Fleischhack, M. Buchovecky, Sanjay Kumar, E. Collins-Hughes, J. Millis, David Kieda, F. Krennrich, Ralph Bird, A. McCann, D. S. Hanna, Q. Feng, N. H. Park, J. P. Finley, V. Bugaev, I. Telezhinsky, Karen Byrum, Jamie Holder, A. Weinstein, O. M. Weiner, N. Kelley-Hoskins, A. Wilhelm, R. A. Ong, M. P. Connolly, Xian Chen, J. Eisch, G. H. Sembroski, R. Mukherjee, L. Ciupik, V. Pelassa, Farhad Yusef-Zadeh, M. Hütten, P. Kar, G. H. Gillanders, J. Grube, Daniel Nieto, D. Staszak, P. Moriarty, E. Pueschel, A. W. Smith, and Gordon T. Richards

Subjects
galaxy: center, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, molecular clouds, Astrophysics::Cosmology and Extragalactic Astrophysics, telescope, 01 natural sciences, supernovae: individual (g0.9+0.1), 0103 physical sciences, emission, center region, chandra observations, Supernova remnant, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Supermassive black hole, 010308 nuclear & particles physics, Molecular cloud, Galactic Center, Institut für Physik und Astronomie, Astronomy and Astrophysics, gamma rays: general, Galactic plane, Galaxy, Black hole, Supernova, Space and Planetary Science, sagittarius b2 cloud, ddc:520, High Energy Physics::Experiment, high-energy, Astrophysics - High Energy Astrophysical Phenomena, sgr-a-asterisk, stellar clusters, center black-hole
Abstract

The astrophysical journal 821(2), 129 (2016). doi:10.3847/0004-637X/821/2/129, The Galactic Center ridge has been observed extensively in the past by both GeV and TeV gamma-ray instrumentsrevealing a wealth of structure, including a diffuse component and the point sources G0.9+0.1 (a compositesupernova remnant) and Sgr A*(believed to be associated with the supermassive black hole located at the center of our Galaxy). Previous very high energy (VHE) gamma-ray observations with the H.E.S.S. experiment have also detected an extended TeV gamma-ray component along the Galactic plane in the > 300 GeV gamma-ray regime. Here we report on observations of the Galactic Center ridge from 2010 to 2014 by the VERITAS telescope array in the > 2 TeV energy range. From these observations we (1) provide improved measurements of the differential energy spectrum for Sgr A* in the > 2 TeV gamma-ray regime, (2) provide a detection in the > 2 TeV gamma-ray emission from the composite SNR G0.9+0.1 and an improved determination of its multi-TeV gamma-ray energy spectrum, and (3) report on the detection of VER J1746-289, a localized enhancement of > 2 TeV gamma-rayemission along the Galactic plane., Published by Univ.11032, Chicago, Ill. [u.a.]

Published
2016
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22. OBSERVATIONS OF THE SHELL-TYPE SUPERNOVA REMNANT CASSIOPEIA A AT TeV ENERGIES WITH VERITAS

Author

R. G. Wagner, Gernot Maier, Stephanie Wissel, C. M. Hui, M. J. Lang, S. P. Wakely, T. B. Humensky, Daniel Gall, B. R. Smith, Geza Gyuk, Y. Butt, D. Boltuch, J. E. Ward, A. Cesarini, John L. Quinn, R. Dickherber, A. J.R. Weinstein, M. Bautista, S. Thibadeau, S. McArthur, V. A. Acciari, D. S. Hanna, David Kieda, J. P. Finley, R. A. Ong, Thomas Weisgarber, N. Karlsson, Jamie Holder, A. McCann, Martin Pohl, Wystan Benbow, T. C. Weekes, M. Beilicke, D. Steele, R. Guenette, V. Bugaev, S. LeBohec, F. Krennrich, E. Roache, P. Fortin, H. J. Rose, J. Grube, A. Furniss, S. P. Swordy, J. Millis, K. Byrum, Matthew J.A. Wood, Tulun Ergin, P. Moriarty, Nicola Galante, J. S. Perkins, M. Kertzman, S. J. Fegan, S. Vincent, M. Schroedter, G. H. Sembroski, P. T. Reynolds, Lucy Fortson, A. Varlotta, Wei Cui, D. Huang, M. Theiling, P. Cogan, T. Aune, Y. C. Chow, V. V. Vassiliev, P. Kaaret, G. Finnegan, A. W. Smith, C. Duke, J. H. Buckley, A. Konopelko, G. H. Gillanders, T. Arlen, L. Ciupik, E. Aliu, H. Krawczynski, K. Ragan, S. M. Bradbury, A. Cannon, D. Pandel, and M. McCutcheon

Subjects
Photon, Astrophysics::High Energy Astrophysical Phenomena, cosmic-rays, Shell (structure), Flux, Astrophysics, 01 natural sciences, Power law, cosmic rays, 0103 physical sciences, air cerenkov telescopes, crab-nebula, Supernova remnant, ism: individual objects (cassiopeia a), 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Cherenkov radiation, acceleration of particles, Physics, magnetic-fields, electron acceleration, particle-acceleration, 010308 nuclear & particles physics, Astrophysics::Instrumentation and Methods for Astrophysics, Gamma ray, Astronomy and Astrophysics, gamma-ray emission, Cassiopeia A, gamma rays: ism, rx j1713.7-3946, 13. Climate action, Space and Planetary Science, ism: supernova remnants, a supernova, magic telescope
Abstract

We report on observations of very high energy gamma rays from the shell-type supernova remnant (SNR) Cassiopeia A with the Very Energetic Radiation Imaging Telescope Array System stereoscopic array of four imaging atmospheric Cherenkov telescopes in Arizona. The total exposure time for these observations is 22 hr, accumulated between September and November of 2007. The gamma-ray source associated with the SNR Cassiopeia A was detected above 200 GeV with a statistical significance of 8.3 sigma. The estimated integral flux for this gamma-ray source is about 3% of the Crab-Nebula flux. The photon spectrum is compatible with a power law dN/dE proportional to E(-Gamma) with an index Gamma = 2.61 +/- 0.24(stat) +/- 0.2(sys). The data are consistent with a point-like source. We provide a detailed description of the analysis results and discuss physical mechanisms that may be responsible for the observed gamma-ray emission.

Published
2010
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23. OBSERVATION OF EXTENDED VERY HIGH ENERGY EMISSION FROM THE SUPERNOVA REMNANT IC 443 WITH VERITAS

Author

R. A. Ong, Thomas Weisgarber, S. LeBohec, S. M. Bradbury, A. Cannon, D. Pandel, D. Horan, P. Cogan, J. Grube, David Kieda, L. Ciupik, P. T. Reynolds, A. McCann, Lucy Fortson, M. Kertzman, M. K. Daniel, E. Aliu, H. Krawczynski, A. Varlotta, Gernot Maier, S. P. Swordy, V. V. Vassiliev, Martin Pohl, S. P. Wakely, Daniel Gall, K. Ragan, M. Wood, M. Beilicke, G. Finnegan, T. B. Humensky, A. W. Smith, B. Zitzer, A. Konopelko, R. G. Wagner, C. Duke, M. Schroedter, L. Valcarcel, Vikram V. Dwarkadas, P. Moriarty, Geza Gyuk, A. Weinstein, T. Arlen, P. Colin, A. N. Otte, A. Furniss, J. H. Buckley, P. Kaaret, Tulun Ergin, F. Krennrich, P. Fortin, S. Vincent, D. S. Hanna, Wystan Benbow, M. Theiling, C. M. Hui, Y. Butt, J. P. Finley, V. Bugaev, G. H. Sembroski, J. A. Toner, T. C. Weekes, R. Dickherber, A. Imran, E. Hays, J. S. Perkins, John Kildea, D. A. Williams, R. Guenette, J. Millis, O. Celik, K. Byrum, Wei Cui, Stephanie Wissel, T. Aune, Y. C. K. Chow, S. J. Fegan, D. Steele, V. A. Acciari, M. J. Lang, H. J. Rose, N. Karlsson, A. Cesarini, John L. Quinn, M. Bautista, K. G. Gibbs, Jamie Holder, L. C. Reyes, E. Roache, J. E. Ward, G. H. Gillanders, S. Godambe, M. McCutcheon, and OpenMETU

Subjects
Physics, nebula, 010308 nuclear & particles physics, ic-443, Molecular cloud, cosmic-rays, Flux, Astronomy and Astrophysics, Context (language use), xmm-newton observations, molecular clouds, Astrophysics, gamma-ray emission, 01 natural sciences, Pulsar wind nebula, ism: individual (ic 443=ver j0616.9+2230, = magic j0616+225), radiation, Space and Planetary Science, 0103 physical sciences, Supernova remnant, 010303 astronomy & astrophysics, gamma rays: observations, magic telescope, discovery, pulsar
Abstract

We present evidence that the very high energy (VHE, E > 100 GeV) gamma-ray emission coincident with the supernova remnant IC 443 is extended. IC 443 contains one of the best studied sites of supernova remnant/molecular cloud interaction and the pulsar wind nebula CXOU J061705.3+222127, both of which are important targets for VHE observations. VERITAS observed IC 443 for 37.9 hr during 2007 and detected emission above 300 GeV with an excess of 247 events, resulting in a significance of 8.3 standard deviations (sigma) before trials and 7.5 sigma after trials in a point-source search. The emission is centered at 6(h)16(m)51(s)+22 degrees 30'11 '' (J2000)+/- 0 degrees.03(stat)+/- 0 degrees.08(sys), with an intrinsic extension of 0 degrees.16 +/- 0 degrees.03(stat)+/- 0 degrees.04(sys). The VHE spectrum is well fit by a power law (dN/dE = N(0) x(E/TeV)(-Gamma)) with a photon index of 2.99 +/- 0.38(stat)+/- 0.3(sys) and an integral flux above 300 GeV of (4.63 +/- 0.90(stat)+/- 0.93(sys)) x 10(-12) cm(-2) s(-1). These results are discussed in the context of existing models for gamma-ray production in IC 443.

Published
2009
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24. EVIDENCE FOR LONG-TERM GAMMA-RAY AND X-RAY VARIABILITY FROM THE UNIDENTIFIED TeV SOURCE HESS J0632+057

Author

V. A. Acciari, E. Aliu, T. Arlen, M. Beilicke, W. Benbow, D. Boltuch, S. M. Bradbury, J. H. Buckley, V. Bugaev, K. Byrum, A. Cannon, A. Cesarini, Y. C. Chow, L. Ciupik, P. Cogan, R. Dickherber, C. Duke, T. Ergin, A. Falcone, S. J. Fegan, J. P. Finley, G. Finnegan, P. Fortin, L. Fortson, A. Furniss, K. Gibbs, G. H. Gillanders, J. Grube, R. Guenette, G. Gyuk, D. Hanna, J. Holder, D. Horan, C. M. Hui, T. B. Humensky, A. Imran, P. Kaaret, N. Karlsson, M. Kertzman, D. Kieda, J. Kildea, A. Konopelko, H. Krawczynski, F. Krennrich, M. J. Lang, S. LeBohec, G. Maier, A. McCann, M. McCutcheon, J. Millis, P. Moriarty, R. Mukherjee, R. A. Ong, A. N. Otte, D. Pandel, J. S. Perkins, D. Petry, M. Pohl, J. Quinn, K. Ragan, L. C. Reyes, P. T. Reynolds, H. J. Rose, M. Schroedter, G. H. Sembroski, A. W. Smith, D. Steele, S. Swordy, M. Theiling, J. A. Toner, A. Varlotta, V. V. Vassiliev, S. Vincent, R. G. Wagner, S. P. Wakely, J. E. Ward, T. C. Weekes, A. Weinstein, T. Weisgarber, D. A. Williams, S. Wissel, and M. Wood

Subjects
stars, catalog, Be star, Astrophysics::High Energy Astrophysical Phenomena, binary, FOS: Physical sciences, Astrophysics, telescope, 01 natural sciences, emission, 0103 physical sciences, 010303 astronomy & astrophysics, acceleration of particles, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, 010308 nuclear & particles physics, stars: individual (hess j0632+057, mwc 148), Gamma ray, X-ray, Astronomy and Astrophysics, Crab Nebula, binaries: general, Space and Planetary Science, Astrophysics - High Energy Astrophysical Phenomena, gamma rays: observations, discovery
Abstract

HESS J0632+057 is one of only two unidentified very-high-energy gamma-ray sources which appear to be point-like within experimental resolution. It is possibly associated with the massive Be star MWC 148 and has been suggested to resemble known TeV binary systems like LS I +61 303 or LS 5039. HESS J0632+057 was observed by VERITAS for 31 hours in 2006, 2008 and 2009. During these observations, no significant signal in gamma rays with energies above 1 TeV was detected from the direction of HESS J0632+057. A flux upper limit corresponding to 1.1% of the flux of the Crab Nebula has been derived from the VERITAS data. The non-detection by VERITAS excludes with a probability of 99.993% that HESS J0632+057 is a steady gamma-ray emitter. Contemporaneous X-ray observations with Swift XRT reveal a factor of 1.8+-0.4 higher flux in the 1-10 keV range than earlier X-ray observations of HESS J0632+057. The variability in the gamma-ray and X-ray fluxes supports interpretation of the ob ject as a gamma-ray emitting binary., Comment: 8 pages, 3 figures, Accepted for publication in The Astrophysical Journal

Published
2009
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25. Status report from VERITAS

Author

Jamie Holder, I. Jung, M. J. Lang, Gernot Maier, S. P. Wakely, R. G. Wagner, D. A. Carter-Lewis, D. Steele, J. S. Perkins, P. Cogan, M. K. Daniel, Henric Krawczynski, David Kieda, E. Hays, John Kildea, Tulun Ergin, G. H. Gillanders, P. Kaaret, K G Gutierrez, A. J.R. Weinstein, Wei Cui, P Fortin, D. Horan, L. Valcarcel, G. E. Kenny, Thomas Brian Humensky, S. P. Swordy, C. Dowdall, David A. Williams, A. D. Falcone, S. J. Fegan, Karen Byrum, Stephanie Wissel, M. Schroedter, Lucy Fortson, S. M. Bradbury, V. V. Vassiliev, F. Pizlo, A. Konopelko, D. S. Hanna, A. Imran, John L. Quinn, G. H. Sembroski, K. G. Gibbs, H. J. Rose, J. H. Buckley, F. Krennrich, S. B. Hughes, Omer Celik, J. A. Toner, G. Blaylock, T. C. Weekes, T. Nagai, P. Moriarty, R. J. White, J. Grube, A. W. Smith, C. Duke, R. A. Ong, S. LeBohec, and J. Millis

Subjects
Physics, History, Observatory, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy, High Energy Physics::Experiment, Astrophysics, Status report, Computer Science Applications, Education
Abstract

VERITAS is a ground-based gamma-ray observatory covering energies between 100 GeV and 50 TeV and will start operating by January 2007. We give a brief report of the construction status and performance characteristics of the telescopes.

Published
2007
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26. Very High Energy Observations of Gamma‐Ray Burst Locations with the Whipple Telescope

Author

M. Schroedter, P. Cogan, J. Grube, R. W. Atkins, Vladimir Vassiliev, Y. C. K. Chow, M. K. Daniel, Karen Byrum, Gernot Maier, P. Fortin, A. D. Falcone, David Kieda, S. P. Wakely, John Kildea, H. Krawczynski, I. de la Calle Perez, Stephan LeBohec, S. P. Swordy, Jeremy Perkins, H. J. Rose, R. A. Ong, J. H. Buckley, R. J. White, K. Ragan, S. J. Fegan, D. Steele, P. T. Reynolds, M. Kertzman, M. J. Lang, Lucy Fortson, S. B. Hughes, R. G. Wagner, G. H. Sembroski, Thomas Brian Humensky, J. Hall, Jamie Holder, S. M. Bradbury, D. J. Fegan, P. Moriarty, John L. Quinn, G. Blaylock, J. P. Finley, T. C. Weekes, K. J. Gutierrez, D. Horan, T. N. Nagai, D. Petry, G. H. Gillanders, Frank Krennrich, C. Dowdall, O. Celik, D. S. Hanna, D. A. Williams, G. E. Kenny, H. M. Badran, John Toner, Wei Cui, L. Valcarcel, and Mark N. Quinn

Subjects
Physics, gamma rays : bursts, gamma rays : observations, Astronomy & Astrophysics, High energy, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Afterglow, law.invention, Telescope, compton emission, refreshed shocks, external matter, light-curve, afterglows, tev, models, flares, discovery, search, Space and Planetary Science, Observatory, law, Spectral energy distribution, Blazar, Gamma-ray burst, Flare
Abstract

Gamma-ray burst (GRB) observations at very high energies (VHE, E > 100 GeV) can impose tight constraints on some GRB emission models. Many GRB afterglow models predict a VHE component similar to that seen in blazars and plerions, in which the GRB spectral energy distribution has a double-peaked shape extending into the VHE regime. VHE emission coincident with delayed X-ray flare emission has also been predicted. GRB follow-up observations have had high priority in the observing program at the Whipple 10m Gamma-ray Telescope and GRBs will continue to be high priority targets as the next generation observatory, VERITAS, comes on-line. Upper limits on the VHE emission, at late times (>~4 hours), from seven GRBs observed with the Whipple Telescope are reported here., Accepted for publication in the January 20, 2007 volume of the Astrophysical Journal, 655, 396

Published
2007
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27. Gamma rays from the quasar PKS 1441+25: story of an escape

Author

Wystan Benbow, S. McArthur, O. M. Weiner, N. Håkansson, Henrike Fleischhack, M. J. Lang, P. Fortin, Ralph Bird, N. Kelley-Hoskins, L. Ciupik, R. Reeves, Geza Gyuk, Paul S. Smith, G. M. Madejski, Martin Pohl, Thomas W.-S. Holoien, A. O'Faolain de Bhroithe, J. Grube, Matthew J. Graham, R. A. Ong, A. McCann, K. Ragan, A. Petrashyk, K. Meagher, E. Pueschel, Marcos Santander, A. Wilhelm, Maria Krause, P. Kar, Benjamin J. Shappee, Talvikki Hovatta, S. G. Djorgovski, Paolo De Coppi, J. Tyler, M. P. Connolly, A. A. Mahabal, G. Ratliff, A. Archer, Xuhui Chen, J. H. Buckley, Lucy Fortson, Jodi Christiansen, S. Archambault, Q. Feng, P. Moriarty, Anthony C. S. Readhead, V. V. Vassiliev, A. Flinders, J. S. Perkins, Reshmi Mukherjee, Abraham D. Falcone, Hugh Dickinson, G. H. Gillanders, Karlen Shahinyan, David Kieda, Y. Khassen, T. B. Humensky, J. V. Tucci, Matteo Cerruti, N. W. Todd, Amy Furniss, G. H. Sembroski, D. S. Hanna, F. Krennrich, Daniel Nieto, A. Popkow, T. J. Pearson, Gernot Maier, J. L. Richards, Christopher S. Kochanek, T. Aune, Moritz Hütten, Wei Cui, John L. Quinn, B. Zitzer, P. Kaaret, J. V. Cardenzana, P. T. Reynolds, Walter Max-Moerbeck, Julien Rousselle, Manel Errando, S. Kumar, S. P. Wakely, C. A. Johnson, J. L. Prieto, Sinéad M. Griffin, Jonathan Biteau, Andrew J. Drake, J. P. Finley, J. P. Dumm, S. Vincent, A. W. Smith, J. D. Eisch, A. Weinstein, Gordon T. Richards, E. Roache, V. Bugaev, K. Z. Stanek, Nahee Park, Anushka Udara Abeysekara, Anna Barnacka, A. N. Otte, I. Telezhinsky, Jamie Holder, David A. Williams, D. Staszak, and ~

Subjects
extragalactic background light, Active galactic nucleus, Cosmology and Nongalactic Astrophysics (astro-ph.CO), spectra, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, telescope, Astrophysical jet, gamma rays: galaxies, emission, complete sample, Astrophysics::Galaxy Astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Supermassive black hole, variability, Gamma ray, Astronomy and Astrophysics, Quasar, radiation mechanisms: non-thermal, Galaxy, diffuse radiation, radiation, Extragalactic background light, mission, Space and Planetary Science, cosmology: observations, ddc:520, Astrophysics - High Energy Astrophysical Phenomena, Schwarzschild radius, absorption, fermi blazars, quasars: individual (pks 1441+25-ver j1443+250), Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract

The astrophysical journal / 2 815(2), L22 -(2015). doi:10.1088/2041-8205/815/2/L22, Outbursts from gamma-ray quasars provide insights on the relativistic jets of active galactic nuclei and constraints on the diffuse radiation fields that fill the universe. The detection of significant emission above 100 GeV from a distant quasar would show that some of the radiated gamma-rays escape pair-production interactions with low-energy photons, be it the extragalactic background light (EBL), or the radiation near the supermassive black hole lying at the jet's base. VERITAS detected gamma-ray emission up to ~200 GeV from PKS 1441+25 (z = 0.939) during 2015 April, a period of high activity across all wavelengths. This observation of PKS 1441+25 suggests that the emission region is located thousands of Schwarzschild radii away from the black hole. The gamma-ray detection also sets a stringent upper limit on the near-ultraviolet to near-infrared EBL intensity, suggesting that galaxy surveys have resolved most, if not all, of the sources of the EBL at these wavelengths., Published by Institute of Physics Publ., London

Published
2015
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28. Multiwavelength observations of Mrk 501 in 2008

Author

MAGIC Collaboration, J. Aleksić(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), S. Ansoldi(Università di Udine, and INFN Trieste, I-33100 Udine, Italy), L. A. Antonelli(INAF National Institute for Astrophysics, I-00136 Rome, Italy), P. Antoranz(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), A. Babic(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), P. Bangale(Max-Planck-Institut für Physik, D-80805 München, Germany), U. Barres de Almeida(Max-Planck-Institut für Physik, D-80805 München, Germany), J. A. Barrio(Universidad Complutense, E-28040 Madrid, Spain), J. Becerra González(Inst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain), W. Bednarek(University of Lodz, PL-90236 Lodz, Poland), K. Berger(Inst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain), E. Bernardini(Deutsches Elektronen-Synchrotron), A. Biland(ETH Zurich, CH-8093 Zurich, Switzerland), O. Blanch(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), R. K. Bock(Max-Planck-Institut für Physik, D-80805 München, Germany), S. Bonnefoy(Universidad Complutense, E-28040 Madrid, Spain), G. Bonnoli(INAF National Institute for Astrophysics, I-00136 Rome, Italy), F. Borracci(Max-Planck-Institut für Physik, D-80805 München, Germany), T. Bretz(Universität Würzburg, D-97074 Würzburg, Germany), E. Carmona(Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, E-28040 Madrid, Spain), A. Carosi(INAF National Institute for Astrophysics, I-00136 Rome, Italy), D. Carreto Fidalgo(Universität Würzburg, D-97074 Würzburg, Germany), P. Colin(Max-Planck-Institut für Physik, D-80805 München, Germany), E. Colombo(Inst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain), J. L. Contreras(Universidad Complutense, E-28040 Madrid, Spain), J. Cortina(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), S. Covino(INAF National Institute for Astrophysics, I-00136 Rome, Italy), P. Da Vela(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), F. Dazzi(Università di Udine, and INFN Trieste, I-33100 Udine, Italy), A. De Angelis(Università di Udine, and INFN Trieste, I-33100 Udine, Italy), G. De Caneva(Deutsches Elektronen-Synchrotron), B. De Lotto(Università di Udine, and INFN Trieste, I-33100 Udine, Italy), C. Delgado Mendez(Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, E-28040 Madrid, Spain), M. Doert(Technische Universität Dortmund, D-44221 Dortmund, Germany), A. Domínguez(Inst. de Astrofísica de Andalucía), D. Dominis Prester(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), D. Dorner(Universität Würzburg, D-97074 Würzburg, Germany), M. Doro(Università di Padova and INFN, I-35131 Padova, Italy), S. Einecke(Technische Universität Dortmund, D-44221 Dortmund, Germany), D. Eisenacher(Universität Würzburg, D-97074 Würzburg, Germany), D. Elsaesser(Universität Würzburg, D-97074 Würzburg, Germany), E. Farina(Università dell'Insubria, Como, I-22100 Como, Italy), D. Ferenc(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), M. V. Fonseca(Universidad Complutense, E-28040 Madrid, Spain), L. Font(Unitat de Física de les Radiacions, Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain), K. Frantzen(Technische Universität Dortmund, D-44221 Dortmund, Germany), C. Fruck(Max-Planck-Institut für Physik, D-80805 München, Germany), R. J. García López(Inst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain), M. Garczarczyk(Deutsches Elektronen-Synchrotron), D. Garrido Terrats(Unitat de Física de les Radiacions, Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain), M. Gaug(Unitat de Física de les Radiacions, Departament de Física, and CERES-IEEC, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain), G. Giavitto(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), N. Godinović(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), A. González Muñoz(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), S. R. Gozzini(Deutsches Elektronen-Synchrotron), A. Hadamek(Technische Universität Dortmund, D-44221 Dortmund, Germany), D. Hadasch(Institut de Ciències de l'Espai), A. Herrero(Inst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain), D. Hildebrand(ETH Zurich, CH-8093 Zurich, Switzerland), J. Hose(Max-Planck-Institut für Physik, D-80805 München, Germany), D. Hrupec(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), W. Idec(University of Lodz, PL-90236 Lodz, Poland), V. Kadenius(Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland), H. Kellermann(Max-Planck-Institut für Physik, D-80805 München, Germany), M. L. Knoetig(ETH Zurich, CH-8093 Zurich, Switzerland), J. Krause(Max-Planck-Institut für Physik, D-80805 München, Germany), J. Kushida(Japanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, Japan), A. La Barbera(INAF National Institute for Astrophysics, I-00136 Rome, Italy), D. Lelas(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), N. Lewandowska(Universität Würzburg, D-97074 Würzburg, Germany), E. Lindfors(Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland), S. Lombardi(INAF National Institute for Astrophysics, I-00136 Rome, Italy), M. López(Universidad Complutense, E-28040 Madrid, Spain), R. López-Coto(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), A. López-Oramas(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), E. Lorenz(Max-Planck-Institut für Physik, D-80805 München, Germany), I. Lozano(Universidad Complutense, E-28040 Madrid, Spain), M. Makariev(Inst. for Nucl. Research and Nucl. Energy, BG-1784 Sofia, Bulgaria), K. Mallot(Deutsches Elektronen-Synchrotron), G. Maneva(Inst. for Nucl. Research and Nucl. Energy, BG-1784 Sofia, Bulgaria), N. Mankuzhiyil(2,*), K. Mannheim(Universität Würzburg, D-97074 Würzburg, Germany), L. Maraschi(INAF National Institute for Astrophysics, I-00136 Rome, Italy), B. Marcote(Universitat de Barcelona), M. Mariotti(Università di Padova and INFN, I-35131 Padova, Italy), M. Martínez(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), D. Mazin(Max-Planck-Institut für Physik, D-80805 München, Germany), U. Menzel(Max-Planck-Institut für Physik, D-80805 München, Germany), M. Meucci(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), J. M. Miranda(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), R. Mirzoyan(Max-Planck-Institut für Physik, D-80805 München, Germany), A. Moralejo(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), P. Munar-Adrover(Universitat de Barcelona), D. Nakajima(Japanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, Japan), A. Niedzwiecki(University of Lodz, PL-90236 Lodz, Poland), K. Nilsson(Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland), N. Nowak(Max-Planck-Institut für Physik, D-80805 München, Germany), R. Orito(Japanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, Japan), A. Overkemping(Technische Universität Dortmund, D-44221 Dortmund, Germany), S. Paiano(Università di Padova and INFN, I-35131 Padova, Italy), M. Palatiello(Università di Udine, and INFN Trieste, I-33100 Udine, Italy), D. Paneque(6,*), R. Paoletti(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), J. M. Paredes(Universitat de Barcelona), X. Paredes-Fortuny(Universitat de Barcelona), S. Partini(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), M. Persic(Università di Udine, and INFN Trieste, I-33100 Udine, Italy), F. Prada(Inst. de Astrofísica de Andalucía), P. G. Prada Moroni(Università di Pisa, and INFN Pisa, I-56126 Pisa, Italy), E. Prandini(Università di Padova and INFN, I-35131 Padova, Italy), S. Preziuso(Università di Siena, and INFN Pisa, I-53100 Siena, Italy), I. Puljak(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), R. Reinthal(Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland), W. Rhode(Technische Universität Dortmund, D-44221 Dortmund, Germany), M. Ribó(Universitat de Barcelona), J. Rico(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), J. Rodriguez Garcia(Max-Planck-Institut für Physik, D-80805 München, Germany), S. Rügamer(Universität Würzburg, D-97074 Würzburg, Germany), A. Saggion(Università di Padova and INFN, I-35131 Padova, Italy), T. Saito(Japanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, Japan), K. Saito(Japanese MAGIC Consortium, Division of Physics and Astronomy, Kyoto University, Japan), M. Salvati(INAF National Institute for Astrophysics, I-00136 Rome, Italy), K. Satalecka(7,*), V. Scalzotto(Università di Padova and INFN, I-35131 Padova, Italy), V. Scapin(Universidad Complutense, E-28040 Madrid, Spain), C. Schultz(Università di Padova and INFN, I-35131 Padova, Italy), T. Schweizer(Max-Planck-Institut für Physik, D-80805 München, Germany), S. N. Shore(Università di Pisa, and INFN Pisa, I-56126 Pisa, Italy), A. Sillanpää(Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland), J. Sitarek(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), I. Snidaric(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), D. Sobczynska(University of Lodz, PL-90236 Lodz, Poland), F. Spanier(Universität Würzburg, D-97074 Würzburg, Germany), V. Stamatescu(IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain), A. Stamerra(INAF National Institute for Astrophysics, I-00136 Rome, Italy), T. Steinbring(Universität Würzburg, D-97074 Würzburg, Germany), J. Storz(Universität Würzburg, D-97074 Würzburg, Germany), S. Sun(Max-Planck-Institut für Physik, D-80805 München, Germany), T. Surić(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), L. Takalo(Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland), F. Tavecchio(INAF National Institute for Astrophysics, I-00136 Rome, Italy), P. Temnikov(Inst. for Nucl. Research and Nucl. Energy, BG-1784 Sofia, Bulgaria), T. Terzić(Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia), D. Tescaro(Inst. de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain), M. Teshima(Max-Planck-Institut für Physik, D-80805 München, Germany), J. Thaele(Technische Universität Dortmund, D-44221 Dortmund, Germany), O. Tibolla(Universität Würzburg, D-97074 Würzburg, Germany), D. F. Torres(Institut de Ciències de l'Espai), T. Toyama(Max-Planck-Institut für Physik, D-80805 München, Germany), A. Treves(Università dell'Insubria, Como, I-22100 Como, Italy), M. Uellenbeck(Technische Universität Dortmund, D-44221 Dortmund, Germany), P. Vogler(ETH Zurich, CH-8093 Zurich, Switzerland), R. M. Wagner(Max-Planck-Institut für Physik, D-80805 München, Germany), F. Zandanel(Inst. de Astrofísica de Andalucía), R. Zanin(Universitat de Barcelona), VERITAS Collaboration(Deutsches Elektronen-Synchrotron), (Deutsches Elektronen-Synchrotron), B. Behera(Deutsches Elektronen-Synchrotron), M. Beilicke(Department of Physics, Washington University, St. Louis, MO 63130, USA), W. Benbow(Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645, USA), R. Bird(School of Physics, University College Dublin, Belfield, Dublin 4, Ireland), A. Bouvier(Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA), V. Bugaev(Department of Physics, Washington University, St. Louis, MO 63130, USA), M. Cerruti(Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645, USA), X. Chen(Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany), L. Ciupik(Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605, USA), E. Collins-Hughes(School of Physics, University College Dublin, Belfield, Dublin 4, Ireland), W. Cui(Department of Physics, Purdue University, West Lafayette, IN 47907, USA), C. Duke(Department of Physics, Grinnell College, Grinnell, IA 50112-1690, USA), J. Dumm(School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA), A. Falcone(Department of Astronomy and Astrophysics, 525 Davey Lab, Pennsylvania State University, University Park, PA 16802, USA), S. Federici(now at GRAPPA Institute, University of Amsterdam, 1098XH), Q. Feng(Department of Physics, Purdue University, West Lafayette, IN 47907, USA), J. P. Finley(Department of Physics, Purdue University, West Lafayette, IN 47907, USA), L. Fortson(School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA), A. Furniss(Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA), N. Galante(Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645, USA), G. H. Gillanders(School of Physics, National University of Ireland Galway, University Road, Galway, Ireland), S. Griffin(Physics Department, McGill University, Montreal, QC H3A 2T8, Canada), S. T. Griffiths(Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, IA 52242, USA), J. Grube(Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605, USA), G. Gyuk(Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605, USA), D. Hanna(Physics Department, McGill University, Montreal, QC H3A 2T8, Canada), J. Holder(Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, DE 19716, USA), C. A. Johnson(Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA), P. Kaaret(Department of Physics and Astronomy, University of Iowa, Van Allen Hall, Iowa City, IA 52242, USA), M. Kertzman(Department of Physics and Astronomy, DePauw University, Greencastle, IN 46135-0037, USA), D. Kieda(Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112, USA), H. Krawczynski(Department of Physics, Washington University, St. Louis, MO 63130, USA), M. J. Lang(School of Physics, National University of Ireland Galway, University Road, Galway, Ireland), A. S Madhavan(Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA), G. Maier(Deutsches Elektronen-Synchrotron), P. Majumdar(Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA), K. Meagher(School of Physics and Center for Relativistic Astrophysics, Georgia Institute of Technology, 837 State Street NW, Atlanta, GA 30332-0430), P. Moriarty(Department of Life and Physical Sciences, Galway-Mayo Institute of Technology, Dublin Road, Galway, Ireland), R. Mukherjee(Department of Physics and Astronomy, Barnard College, Columbia University, NY 10027, USA), D. Nieto(Physics Department, Columbia University, New York, NY 10027, USA), A. O'Faoláin de Bhróithe(School of Physics, University College Dublin, Belfield, Dublin 4, Ireland), R. A. Ong(Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA), A. N. Otte(School of Physics and Center for Relativistic Astrophysics, Georgia Institute of Technology, 837 State Street NW, Atlanta, GA 30332-0430), A. Pichel(Instituto de Astronomia y Fisica del Espacio, Casilla de Correo 67 - Sucursal 28), M. Pohl(Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany), A. Popkow(Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA), H. Prokoph(Deutsches Elektronen-Synchrotron), J. Quinn(School of Physics, University College Dublin, Belfield, Dublin 4, Ireland), J. Rajotte(Physics Department, McGill University, Montreal, QC H3A 2T8, Canada), G. Ratliff(Astronomy Department, Adler Planetarium and Astronomy Museum, Chicago, IL 60605, USA), L. C. Reyes(Physics Department, California Polytechnic State University, San Luis Obispo, CA 94307, USA), P. T. Reynolds(Department of Applied Physics and Instrumentation, Cork Institute of Technology, Bishopstown, Cork, Ireland), G. T. Richards(School of Physics and Center for Relativistic Astrophysics, Georgia Institute of Technology, 837 State Street NW, Atlanta, GA 30332-0430), E. Roache(Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645, USA), G. H. Sembroski(Department of Physics, Purdue University, West Lafayette, IN 47907, USA), K. Shahinyan(School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA), F. Sheidaei(Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112, USA), A. W. Smith(Department of Physics and Astronomy, University of Utah, Salt Lake City, UT 84112, USA), D. Staszak(Physics Department, McGill University, Montreal, QC H3A 2T8, Canada), I. Telezhinsky(Institute of Physics and Astronomy, University of Potsdam, 14476 Potsdam-Golm, Germany), M. Theiling(Department of Physics, Purdue University, West Lafayette, IN 47907, USA), J. Tyler(Physics Department, McGill University, Montreal, QC H3A 2T8, Canada), A. Varlotta(Department of Physics, Purdue University, West Lafayette, IN 47907, USA), S. Vincent(Deutsches Elektronen-Synchrotron), S. P. Wakely(Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, USA), T. C. Weekes(Fred Lawrence Whipple Observatory, Harvard-Smithsonian Center for Astrophysics, Amado, AZ 85645, USA), R. Welsing(Deutsches Elektronen-Synchrotron), D. A. Williams(Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA), A. Zajczyk(Department of Physics, Washington University, St. Louis, MO 63130, USA), B. Zitzer(Argonne National Laboratory, 9700 S. Cass Avenue, Argonne, IL 60439, USA), External Collaborators(INAF, Osservatorio Astronomico di Torino, I-10025 Pino Torinese), (INAF, Osservatorio Astronomico di Torino, I-10025 Pino Torinese), M. Villata(INAF, Osservatorio Astronomico di Torino, I-10025 Pino Torinese), C. M. Raiteri(INAF, Osservatorio Astronomico di Torino, I-10025 Pino Torinese), M. Ajello(Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450, USA), M. Perri(ASI-Science Data Center, Via del Politecnico, I-00133 Rome, Italy), H. D. Aller(Department of Astronomy, University of Michigan, Ann Arbor, MI 48109-1042, USA), M. F. Aller(Department of Astronomy, University of Michigan, Ann Arbor, MI 48109-1042, USA), V. M. Larionov(Astron. Inst., St.-Petersburg State Univ., Russia), N. V. Efimova(Astron. Inst., St.-Petersburg State Univ., Russia), T. S. Konstantinova(Astron. Inst., St.-Petersburg State Univ., Russia), E. N. Kopatskaya(Astron. Inst., St.-Petersburg State Univ., Russia), W. P. Chen(Graduate Institute of Astronomy, National Central University, 300 Jhongda Rd., Jhongli 32001, Taiwan), E. Koptelova(Graduate Institute of Astronomy, National Central University, 300 Jhongda Rd., Jhongli 32001, Taiwan), H. Y. Hsiao(Graduate Institute of Astronomy, National Central University, 300 Jhongda Rd., Jhongli 32001, Taiwan), O. M. Kurtanidze(Abastumani Observatory, Mt. Kanobili, 0301 Abastumani, Georgia), M. G. Nikolashvili(Abastumani Observatory, Mt. Kanobili, 0301 Abastumani, Georgia), G. N. Kimeridze(Abastumani Observatory, Mt. Kanobili, 0301 Abastumani, Georgia), B. Jordan(School of Cosmic Physics, Dublin Institute For Advanced Studies, Ireland), P. Leto(INAF - Osservatorio Astrofisico di Catania, Italy), C. S. Buemi(INAF - Osservatorio Astrofisico di Catania, Italy), C. Trigilio(INAF - Osservatorio Astrofisico di Catania, Italy), G. Umana(INAF - Osservatorio Astrofisico di Catania, Italy), A. Lahtenmaki(Aalto University Metsähovi Radio Observatory Metsähovintie 114 FIN-02540 Kylmälä Finland), E. Nieppola(Aalto University Metsähovi Radio Observatory Metsähovintie 114 FIN-02540 Kylmälä Finland), M. Tornikoski(Aalto University Metsähovi Radio Observatory Metsähovintie 114 FIN-02540 Kylmälä Finland), J. Sainio(Finnish MAGIC Consortium, Tuorla Observatory, University of Turku and Department of Physics, University of Oulu, Finland), M. Giroletti(INAF Istituto di Radioastronomia, 40129 Bologna, Italy), A. Cesarini(University of Trento, Department of Physics, I38050 Povo, Trento, Italy), L. Fuhrmann(Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany), Yu. A. Kovalev(Astro Space Center of the Lebedev Physical Institute, 117997), Y. Y. Kovalev(Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany), Anne Lähteenmäki Group, Department of Radio Science and Engineering, Aalto-yliopisto, Aalto University, Universitat de Barcelona, School services, ELEC, and ~

Subjects
extragalactic background light, Ciencias Físicas, Flux, Electron, Astrophysics, 7. Clean energy, law.invention, purl.org/becyt/ford/1 [https], Raigs gamma, bl lacertae objects, law, individual: Mrk 501 [BL Lacertae objects], Physics, High Energy Astrophysical Phenomena (astro-ph.HE), astro-ph.HE, 213 Electronic, automation and communications engineering, electronics, Astroparticle physics, BL Lacertae objects: individual: Mrk 501, Gamma rays: general, Astronomy and Astrophysics, Space and Planetary Science, Synchrotron, individual: Mrk 50 [BL Lacertae objects], Homogeneous, astroparticle physics, Spectral energy distribution, Electrónica, Física nuclear, Electricidad, Astrophysics - High Energy Astrophysical Phenomena, CIENCIAS NATURALES Y EXACTAS, 1171 Geosciences, Astrophysics::High Energy Astrophysical Phenomena, emitting electrons, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, 114 Physical sciences, bl lacertae objects: individual: mrk 501, crab-nebula, Blazar, Astrophysics::Galaxy Astrophysics, tev blazars, variability, 221 Nanotechnology, Gamma rays, Individual: Mrk 501, Institut für Physik und Astronomie, purl.org/becyt/ford/1.3 [https], gamma rays: general, Galaxies, gamma-ray emission, telescope system, Galàxies, Active Galaxies, blazars, gamma-rays, Mrk 501, Astronomía, Crab Nebula, x-ray, 115 Astronomy and space science, Low emission, 216 Materials engineering, Galàxies actives, active galactic nuclei, Active galaxies, ddc:520, general [gamma rays]
Abstract

Mrk 501 is one of the brightest blazars at TeV energies and has been extensively studied since its first VHE detection in 1996. Our goal is to characterize in detail the source gamma-ray emission, together with the radio-to-X-ray emission, during the non-flaring (low) activity, which is less often studied than the occasional flaring (high) activity. We organized a multiwavelength (MW) campaign on Mrk 501 between March and May 2008. This multi-instrument effort included the most sensitive VHE gamma-ray instruments in the northern hemisphere, namely the imaging atmospheric Cherenkov telescopes MAGIC and VERITAS, as well as Swift, RXTE, the F-GAMMA, GASP-WEBT, and other collaborations and instruments. Mrk 501 was found to be in a low state of activity during the campaign, with a VHE flux in the range of 10%-20% of the Crab nebula flux. Nevertheless, significant flux variations were detected with various instruments, with a trend of increasing variability with energy. The broadband spectral energy distribution during the two different emission states of the campaign can be adequately described within the homogeneous one-zone synchrotron self-Compton model, with the (slightly) higher state described by an increase in the electron number density. This agrees with previous studies of the broadband emission of this source during flaring and non-flaring states. We report for the first time a tentative X-ray-to-VHE correlation during a low VHE activity. Although marginally significant, this positive correlation between X-ray and VHE, which has been reported many times during flaring activity, suggests that the mechanisms that dominate the X-ray/VHE emission during non-flaring-activity are not substantially different from those that are responsible for the emission during flaring activity., Comment: Accepted for publication in A&A

Published
2015
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29. The most powerful flaring activity from the NLSy1 PMN J0948+0022

Author

V. Bugaev, D. Staszak, J. P. Finley, Daniel Nieto, K. Ragan, T. B. Humensky, Josefin Larsson, Reshmi Mukherjee, K. Meagher, Talvikki Hovatta, G. H. Sembroski, L. Ciupik, P. Fortin, Abraham D. Falcone, J. V. Tucci, Gernot Maier, B. Zitzer, Ralph Bird, J. Tyler, Wystan Benbow, J. Grube, Manel Errando, S. Kumar, R. A. Ong, C. M. Raiteri, S. P. Wakely, S. T. Griffiths, Filippo D'Ammando, J. D. Eisch, K. Berger, Julien Rousselle, Hugh Dickinson, A. Weinstein, M. J. Lang, P. Kar, David A. Williams, John L. Quinn, N. Håkansson, Henrike Fleischhack, A. Varlotta, A. N. Otte, A. O'Faolain de Bhroithe, A. W. Smith, A. McCann, A. Popkow, Geza Gyuk, I. Telezhinsky, G. H. Gillanders, Gordon T. Richards, E. Roache, Jamie Holder, F. Krennrich, Marcos Santander, Matteo Cerruti, Walter Max-Moerbeck, Anthony C. S. Readhead, H. Prokoph, J. S. Perkins, David Kieda, J. V. Cardenzana, M. Pohl, Amy Furniss, L. Gérard, P. Moriarty, Matthias Beilicke, Lucy Fortson, M. Kertzman, J. L. Richards, Xuhui Chen, Y. Khassen, Vladimir Vassiliev, M. Orienti, E. Pueschel, P. T. Reynolds, Justin D. Finke, R. Welsing, Aalto-yliopisto, Aalto University, D'Ammando, F., Orienti, M., Finke, J., Raiteri, C. M., Hovatta, T., Larsson, J., Max-Moerbeck, W., Perkins, J., Readhead, A. C. S., Richards, J. L., Beilicke, M., Benbow, W., Berger, K., Bird, R., Bugaev, V., Cardenzana, J. V., Cerruti, M., Chen, X., Ciupik, L., Dickinson, H. J., Eisch, J. D., Errando, M., Falcone, A., Finley, J. P., Fleischhack, H., Fortin, P., Fortson, L., Furniss, A., Gerard, L., Gillanders, G. H., Griffiths, S. T., Grube, J., Gyuk, G., Håkansson, N., Holder, J., Humensky, T. B., Kar, P., Kertzman, M., Khassen, Y., Kieda, D., Krennrich, F., Kumar, S., Lang, M. J., Maier, G., Mccann, A., Meagher, K., Moriarty, P., Mukherjee, R., Nieto, D., de Bhróithe, A. O'Faoláin, Ong, R. A., Otte, A. N., Pohl, M., Popkow, A., Prokoph, H., Pueschel, E., Quinn, J., Ragan, K., Reynolds, P. T., Richards, G. T., Roache, E., Rousselle, J., Santander, M., Sembroski, G. H., Smith, A. W., Staszak, D., Telezhinsky, I., Tucci, J. V., Tyler, J., Varlotta, A., Vassiliev, V. V., Wakely, S. P., Weinstein, A., Welsing, R., Williams, D. A., and Zitzer, B.

Subjects
extragalactic background light, multiwavelength observations, Active galactic nucleus, spectrum radio quasars, individual: PMN J0948+0022 [galaxies], Astrophysics::High Energy Astrophysical Phenomena, galaxies: active, nuclei [galaxies], FOS: Physical sciences, galaxies: active, galaxies: individual: PMN J0948+0022, galaxies: nuclei, galaxies: Seyfert, gamma-rays: general, Owens Valley Radio Observatory, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 7. Clean energy, galaxies: active-galaxies: individual: pmn j0948+0022, line seyfert 1, Luminosity, law.invention, Telescope, law, Seyfert [galaxies], quasar pks 1510-089, relativistic jets, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, galactic nuclei, ta115, ta213, galaxies: individual: PMN J0948+0022, Astronomy, Astronomy and Astrophysics, gamma-rays: general, gamma-ray emission, galaxies: Seyfert, large-area telescope, x-ray, 13. Climate action, Space and Planetary Science, active [galaxies], ddc:520, Spectral energy distribution, galaxies: nuclei, Astrophysics - High Energy Astrophysical Phenomena, Radio astronomy, Flare, Fermi Gamma-ray Space Telescope, general [gamma-rays]
Abstract

Monthly notices of the Royal Astronomical Society 446(3), 2456 - 2467 (2015). doi:10.1093/mnras/stu2251, We report on multifrequency observations performed during 2012 December–2013 August of the first narrow-line Seyfert 1 galaxy detected in $\gamma$-rays, PMN J0948+0022 (z = 0.5846). A γ-ray flare was observed by the Large Area Telescope on board Fermi during 2012 December–2013 January, reaching a daily peak flux in the 0.1–100 GeV energy range of (155 $\pm$ 31) × $10^{−8}$ ph $cm^{−2} s^{−1}$ on 2013 January 1, corresponding to an apparent isotropic luminosity of $\sim$ 1.5 × $10^{48}$ erg $s^{−1}$. The $\gamma$-ray flaring period triggered Swift and Very Energetic Radiation Imaging Telescope Array System (VERITAS) observations in addition to radio and optical monitoring by Owens Valley Radio Observatory, Monitoring Of Jets in Active galactic nuclei with VLBA Experiments, and Catalina Real-time Transient Survey. A strong flare was observed in optical, UV, and X-rays on 2012 December 30, quasi-simultaneously to the $\gamma$-ray flare, reaching a record flux for this source from optical to $\gamma$-rays. VERITAS observations at very high energy (E > 100 GeV) during 2013 January 6–17 resulted in an upper limit of $F_{>0.2 TeV}$ < 4.0 × $10^{−12} ph cm^{−2} s^{−1}$. We compared the spectral energy distribution (SED) of the flaring state in 2013 January with that of an intermediate state observed in 2011. The two SEDs, modelled as synchrotron emission and an external Compton scattering of seed photons from a dust torus, can be modelled by changing both the electron distribution parameters and the magnetic field., Published by Oxford Univ. Press, Oxford

Published
2015
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30. Deployment of the VERITAS observatory

Author

S. P. Swordy, R. A. Ong, J. H. Buckley, M Schroedter, H. Manseri, Gernot Maier, F. Pizlo, S. LeBohec, D Horana, J. Lloyd-Evans, S. P. Wakely, G. Walker, Mark N. Quinn, G. Blaylock, J. Knapp, J. Hall, I. H. Bond, K. Ragan, H. M. Badran, F. Krennrich, R. W. Atkins, Vladimir Vassiliev, David Kieda, M. J. Lang, Martin Pohl, K. Kosack, P T Reynolds, Sm Bradbury, John L. Quinn, R. G. Wagner, D. Petry, K. G. Gibbs, Jeremy Perkins, S. Gammell, P Rebillot, E. Hays, P. A. Ogden, A. Syson, Reshmi Mukherjee, G. H. Gillanders, Jamie Holder, C Duke, Da Carter-Lewis, P. Fortin, H. J. Rose, D. J. Fegan, Y. C. Chow, G H Sembroski, Lucy Fortson, B. Power-Mooney, P. Moriarty, T Ergin, Dowdall, J. Grube, T. N. Nagai, A. D. Falcone, M K Daniel, M. A. Olevitch, David A. Williams, John Kildea, J. P. Finley, Henric Krawczynski, T. C. Weekes, R. J. White, S. B. Hughes, M. Kertzmann, Thomas Brian Humensky, P. Cogan, P. J. Boyle, S. J. Fegan, D. Steele, Paul Dowkontt, D. S. Hanna, W CuP, Jeffrey Zweerink, O. Celik, A. Milovanovic, G. E. Kenny, I. de la Calle Perez, P. Kaaret, E. Linton, and L. Valcarcel

Subjects
Physics, History, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, Gamma ray, Radiation imaging, Astronomy, Cherenkov Telescope Array, Computer Science Applications, Education, law.invention, Telescope, Observatory, Software deployment, law, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Galaxy Astrophysics, Cherenkov radiation
Abstract

The Very Energetic Radiation Imaging Telescope Array System (VERITAS) being constructed in Southern Arizona consists of an array of four Atmospheric Cherenkov 12m Telescopes designed to observe astrophysical gamma rays in the energy range from 100 GeV to tens of TeV. A first telescope has been in operation on a temporary site since the end of 2004 and meets all specifications. The second is being installed on the same site, 85m from the first, in order to test stereoscopic capabilities. The full system of four telescopes is expected to be installed on the definitive site by the end of 2006.

Published
2006
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31. Multiwavelength Observations of the Blazar Markarian 421 in 2002 December and 2003 January

Author

P. F. Rebillot, H. M. Badran, G. Blaylock, S. M. Bradbury, J. H. Buckley, D. A. Carter‐Lewis, O. Celik, Y. C. Chow, P. Cogan, W. Cui, M. Daniel, C. Duke, A. Falcone, S. J. Fegan, J. P. Finley, L. F. Fortson, G. H. Gillanders, J. Grube, K. Gutierrez, G. Gyuk, D. Hanna, J. Holder, D. Horan, S. B. Hughes, G. E. Kenny, M. Kertzman, D. Kieda, J. Kildea, K. Kosack, H. Krawczynski, F. Krennrich, M. J. Lang, S. Le Bohec, E. Linton, G. Maier, P. Moriarty, J. Perkins, M. Pohl, J. Quinn, K. Ragan, P. T. Reynolds, H. J. Rose, M. Schroedter, G. H. Sembroski, G. Steele, S. P. Swordy, L. Valcarcel, V. V. Vassiliev, S. P. Wakely, T. C. Weekes, J. Zweerink, (The VERITAS Collaboration), M. Aller, H. Aller, P. Boltwood, I. Jung, D. Kranich, K. Nilsson, M. Pasanen, A. Sadun, and A. Sillanpaa

Subjects
tev gamma-rays, Astrophysics::High Energy Astrophysical Phenomena, media_common.quotation_subject, bl-lacertae objects, bl lacertae objects : individual (mrk 421), Astrophysics, 01 natural sciences, Radio spectrum, law.invention, law, spectral evolution, Target of opportunity, 0103 physical sciences, strong flares, crab-nebula, 010306 general physics, Blazar, 010303 astronomy & astrophysics, media_common, mechanisms : nonthermal, Physics, HEGRA, Astronomy and Astrophysics, lac objects, Light curve, galaxies : jets, mkn 501, Crab Nebula, x-ray, Space and Planetary Science, Sky, active galactic nuclei, gamma rays : observations radiation, self-compton model, x-rays : individual (mrk 421), Flare
Abstract

We report on a multiwavelength campaign on the TeV gamma-ray blazar Mrk 421 performed during 2002 December and 2003 January. These target of opportunity observations were initiated by the detection of X-ray and TeV gamma-ray flares with the All Sky Monitor (ASM) on board the Rossi X-Ray Timing Explorer (RXTE) and the 10 m Whipple gamma-ray telescope. The campaign included observational coverage in the radio (University of Michigan Radio Astronomy Observatory), optical (Boltwood, La Palma KVA 0.6 m; WIYN 0.9 m), X-ray (RXTE pointed telescopes), and TeV gamma-ray (Whipple and HEGRA) bands. At TeV energies, the observations revealed several flares at intermediate flux levels, peaking between 1 and 1.5 times the flux from the Crab Nebula. While the time-averaged spectrum can be fitted with a single power law of photon index Gamma = 2.8 from dN gamma/dE proportional to E-Gamma, we find some evidence for spectral variability. Confirming earlier results, the campaign reveals a rather loose correlation between the X-ray and TeV gamma-ray fluxes. In one case, a very strong X-ray flare is not accompanied by a comparable TeV gamma-ray flare. Although the source flux was variable in the optical and radio bands, the sparse sampling of the optical and radio light curves does not allow us to study the correlation properties in detail. We present a simple analysis of the data with a synchrotron self-Compton model, emphasizing that models with very high Doppler factors and low magnetic fields can describe the data.

Published
2006
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32. A Survey of Unidentified EGRET Sources at Very High Energies

Author

J. McEnery, A. M. Hillas, O. Celik, J. H. Buckley, C. Duke, J. Grube, A. Syson, Dietrich Müller, David Kieda, J. Lloyd-Evans, A. Jarvis, J. Hall, K. Ragan, Reshmi Mukherjee, K. Kosack, P. Moriarty, F. Krennrich, V. V. Vassiliev, M. K. Daniel, G. H. Sembroski, J. Knapp, Wei Cui, B. Power-Mooney, D. J. Fegan, S. P. Swordy, Jamie Holder, I. de la Calle Perez, P. T. Reynolds, S. P. Wakely, G. Walker, S. J. Fegan, R. A. Ong, S. Le Bohec, G. E. Kenny, I. H. Bond, M. Schroedter, J. P. Finley, R. Pallassini, T. C. Weekes, Lucy Fortson, M. Jordan, M. Catanese, D. Petry, John Kildea, D. S. Hanna, P. Rebillot, P. J. Boyle, E. Linton, Henric Krawczynski, D. A. Carter-Lewis, H. M. Badran, M. D'Vali, Tony Hall, Mark N. Quinn, M. J. Lang, J. A. Gaidos, S. J. Nolan, A. Milovanovic, R. W. Lessard, Jeffrey Zweerink, H. J. Rose, S. M. Bradbury, Abraham D. Falcone, M. Kertzman, D. Horan, John L. Quinn, K. G. Gibbs, S. Gammell, T. N. Nagai, and G. H. Gillanders

Subjects
tev energies, Astrophysics::High Energy Astrophysical Phenomena, sax j0635+0533, Flux, error box, Astrophysics, galactic plane, law.invention, Telescope, surveys, supernova-remnants, galaxies : jets, gamma rays : observations, gamma-ray sources, source 3eg j2227+6122, x-ray, ls i+61-degrees-303, galaxy clusters, Observatory, law, Egret, Astrophysics::Galaxy Astrophysics, Galaxy cluster, Physics, biology, Astronomy, Astronomy and Astrophysics, Galactic plane, biology.organism_classification, Galaxy, Space and Planetary Science
Abstract

The Whipple Observatory 10 m γ-ray telescope has been used to survey the error boxes of EGRET unidentified sources in an attempt to find counterparts at energies of 350 GeV and above. Twenty-one unidentified sources detected by EGRET (more than 10% of the total number) have been included in this survey. In no case is a statistically significant signal found in the EGRET error box, which implies that, at least for this sample, the γ-ray spectra of these sources steepen between 100 MeV and 350 GeV. For each EGRET source location, we list candidate associations and derive upper limits on the integral γ-ray flux above 350 GeV.

Published
2005
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33. Spectrum of Very High Energy Gamma‐Rays from the blazar 1ES 1959+650 during Flaring Activity in 2002

Author

M. K. Daniel, H. M. Badran, I. H. Bond, P. J. Boyle, S. M. Bradbury, J. H. Buckley, D. A. Carter‐Lewis, M. Catanese, O. Celik, P. Cogan, W. Cui, M. D’Vali, I. de la Calle Perez, C. Duke, A. Falcone, D. J. Fegan, S. J. Fegan, J. P. Finley, L. F. Fortson, J. A. Gaidos, S. Gammell, K. Gibbs, G. H. Gillanders, J. Grube, J. Hall, T. A. Hall, D. Hanna, A. M. Hillas, J. Holder, D. Horan, T. B. Humensky, A. Jarvis, M. Jordan, G. E. Kenny, M. Kertzman, D. Kieda, J. Kildea, J. Knapp, K. Kosack, H. Krawczynski, F. Krennrich, M. J. Lang, S. Le Bohec, E. Linton, J. Lloyd‐Evans, A. Milovanovic, P. Moriarty, D. Muller, T. Nagai, S. Nolan, R. A. Ong, R. Pallassini, D. Petry, B. Power‐Mooney, J. Quinn, M. Quinn, K. Ragan, P. Rebillot, P. T. Reynolds, H. J. Rose, M. Schroedter, G. H. Sembroski, S. P. Swordy, A. Syson, V. V. Vassiliev, S. P. Wakely, G. Walker, T. C. Weekes, and J. Zweerink

Subjects
tev energies, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, system, techniques : spectroscopic, law.invention, Telescope, project, law, Coincident, bl lacertae objects : individual (1es 1959+650), gamma rays : observations, strong flares, Blazar, Cherenkov radiation, Physics, Spectral index, Range (particle radiation), Astrophysics (astro-ph), Gamma ray, h1426+428, Astronomy and Astrophysics, calibration, radiation, Space and Planetary Science, cherenkov telescopes, markarian-421, High Energy Physics::Experiment, Flare
Abstract

The blazar 1ES 1959+650 was observed in a flaring state with the Whipple 10 m Imaging Atmospheric Cherenkov Telescope during May of 2002. A spectral analysis has been carried out on the data from that time period and the resulting very high energy gamma-ray spectrum ($E \geq 316$ GeV) can be well fit by a power-law of differential spectral index \alpha = 2.78 +/- 0.12_{stat.} +/- 0.21_{sys.}. On June 4th 2002, the source flared dramatically in the gamma-ray range without any coincident increase in the X-ray emission, providing the first unambiguous example of an `orphan' gamma-ray flare from a blazar. The gamma-ray spectrum for these data can also be described by a simple power-law fit with \alpha = 2.82 +/- 0.15_{stat.} +/- 0.30_{sys.}. There is no compelling evidence for spectral variability, or for any cut-off to the spectrum., Comment: 25 pages. Collaboration website at http://veritas.sao.arizona.edu/

Published
2005
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34. VERITAS: the Very Energetic Radiation Imaging Telescope Array System

Author

M. K. Daniel, S. P. Wakely, G. Walker, John Kildea, J. H. Buckley, David Kieda, Mark N. Quinn, A. Jarvis, S. M. Bradbury, S. P. Swordy, A. Milovanovic, Wei Cui, A. Syson, D. Horan, F. Krennrich, M. Schroedter, V. V. Vassiliev, Abraham D. Falcone, G. E. Kenny, H. J. Rose, R. Pallassini, Lucy Fortson, P. J. Boyle, E. Linton, D. S. Hanna, J. A. Gaidos, M. D'Vali, P. Moriarty, S. J. Nolan, M. Jordan, Jeffrey Zweerink, J. Hall, K. Ragan, Tony Hall, J. Knapp, K. Kosack, D. A. Carter-Lewis, D. Petry, J. Lloyd-Evans, Dietrich Müller, G. H. Gillanders, B. Power-Mooney, G. H. Sembroski, Jamie Holder, S. LeBohec, I. de la Calle Perez, I. H. Bond, M. J. Lang, S. J. Fegan, Henric Krawczynski, M. Kertzman, T. N. Nagai, J. Grube, P. Rebillot, P. T. Reynolds, J. P. Finley, C. Duke, T. C. Weekes, D. J. Fegan, John L. Quinn, K. G. Gibbs, R. A. Ong, S. Gammell, A. M. Hillas, and O. Celik

Subjects
Physics, tev energies, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy, Astronomy and Astrophysics, Gamma-ray astronomy, Astrophysics, First light, Cherenkov Telescope Array, law.invention, Telescope, Primary mirror, Space and Planetary Science, law, Observatory, gamma-ray astronomy, atmospheric cherenkov detectors, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Astrophysics::Galaxy Astrophysics, Very Energetic, Cherenkov radiation
Abstract

The Very Energetic Radiation Imaging Telescope Array System (VERITAS) is the major next generation imaging atmospheric Cherenkov γ-ray telescope in the western hemisphere and will be located in southern Arizona nearby Kitt Peak National Observatory. The VERITAS observatory will provide unprecedented sensitivity to photon energies between 50 GeV and 50 TeV. The first stage is an array of four telescopes to be fully operational in early 2006, with an expansion to seven telescopes envisioned for 2008. The construction of a prototype telescope is underway, for which first light is expected in Fall 2003. The technical concept is outlined and a progress report is given.

Published
2004
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35. Discovery of Very-high-energy Emission from RGB J2243+203 and Derivation of Its Redshift Upper Limit

Author

D. Staszak, Daniel Nieto, M. J. Lang, Marcos Santander, Moritz Hütten, M. P. Connolly, Anushka Udara Abeysekara, M. Buchovecky, N. Kelley-Hoskins, Sinéad M. Griffin, David A. Williams, John L. Quinn, P. Moriarty, R. A. Ong, Q. Feng, Ralph Bird, J. Grube, I. Telezhinsky, Wystan Benbow, M. Kertzman, Lucy Fortson, Maria Krause, M. Poh, P. Wilcox, E. Roache, A. Archer, P. T. Reynolds, Gordon T. Richards, A. N. Otte, J. Tyler, J. H. Buckley, F. Krennrich, Jamie Holder, A. Wilhelm, S. McArthur, V. Bugaev, O. Hervet, O. M. Weiner, Henrike Fleischhack, P. Kaaret, David Kieda, V. V. Vassiliev, Abraham D. Falcone, Karlen Shahinyan, A. Weinstein, J. P. Finley, Matteo Cerruti, Amy Furniss, N. H. Park, Gernot Maier, S. P. Wakely, C. A. Johnson, G. H. Gillanders, E. Puesche, B. Zitzer, K. Ragan, S. Kumar, T. B. Humensky, A. Popkow, I. Sadeh, S. Archambault, S. O'Brien, R. Mukherjee, D. S. Hanna, G. H. Sembroski, Robert Brose, C. Rulten, A. Petrashyk, P. Kar, and Wei Cui

Subjects
extragalactic background light, catalog, Photon, Astrophysics::High Energy Astrophysical Phenomena, blazars, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, telescope, 01 natural sciences, Power law, bl lacertae objects, galaxies: individual (rgb j2243+203), 0103 physical sciences, Blazar, Electronic band structure, 010303 astronomy & astrophysics, parameters, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Spectral index, 010308 nuclear & particles physics, Institut für Physik und Astronomie, Astronomy and Astrophysics, Cherenkov Telescope Array, Redshift, Space and Planetary Science, ddc:520, Astrophysics - High Energy Astrophysical Phenomena, Fermi Gamma-ray Space Telescope
Abstract

Very-high-energy (VHE; $>$ 100 GeV) gamma-ray emission from the blazar RGB J2243+203 was discovered with the VERITAS Cherenkov telescope array, during the period between 21 and 24 December 2014. The VERITAS energy spectrum from this source can be fit by a power law with a photon index of $4.6 \pm 0.5$, and a flux normalization at 0.15 TeV of $(6.3 \pm 1.1) \times 10^{-10} ~ \textrm{cm}^{-2} \textrm{s}^{-1} \textrm{TeV}^{-1}$. The integrated \textit{Fermi}-LAT flux from 1 GeV to 100 GeV during the VERITAS detection is $(4.1 \pm 0.8) \times 10^{\textrm{-8}} ~\textrm{cm}^{\textrm{-2}}\textrm{s}^{\textrm{-1}}$, which is an order of magnitude larger than the four-year-averaged flux in the same energy range reported in the 3FGL catalog, ($4.0 \pm 0.1 \times 10^{\textrm{-9}} ~ \textrm{cm}^{\textrm{-2}}\textrm{s}^{\textrm{-1}}$). The detection with VERITAS triggered observations in the X-ray band with the \textit{Swift}-XRT. However, due to scheduling constraints \textit{Swift}-XRT observations were performed 67 hours after the VERITAS detection, not simultaneous with the VERITAS observations. The observed X-ray energy spectrum between 2 keV and 10 keV can be fitted with a power-law with a spectral index of $2.7 \pm 0.2$, and the integrated photon flux in the same energy band is $(3.6 \pm 0.6) \times 10^{-13} ~\textrm{cm}^{-2} \textrm{s}^{-1}$. EBL model-dependent upper limits of the blazar redshift have been derived. Depending on the EBL model used, the upper limit varies in the range from z $

Published
2017
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36. Unprecedented study of the broadband emission of Mrk 421 during flaring activity in March 2010

Author

E. Pueschel, J. Hose, Svetlana G. Jorstad, M. F. Aller, David A. Williams, G. H. Sembroski, D. Nakajima, M. Strzys, R. Welsing, A. Archer, E. Colombo, B. Biasuzzi, F. Borracci, Stefano Ansoldi, Riccardo Paoletti, I. Telezhinsky, Jamie Holder, D. Elsaesser, D. Staszak, Dario Hrupec, L. Ciupik, L. C. Reyes, G. Bonnoli, K. Ragan, M. A. Lopez, N. Galante, Hajime Takami, J. M. Paredes, P. T. Reynolds, Natalia Lewandowska, Hugh D. Aller, L. O. Takalo, G. H. Gillanders, T. Schweizer, Mosè Mariotti, Wystan Benbow, A.-K. Overkemping, D. Hadasch, Victor Stamatescu, J. Biteau, Paul S. Smith, Gordon T. Richards, Wei Cui, A. La Barbera, Sinéad M. Griffin, E. Roache, A. López-Oramas, S. Rügamer, Juan Abel Barrio, J. A. Ros, O. M. Kurtanidze, Alessandro Carosi, Ruben Lopez-Coto, X. Paredes-Fortuny, Mark Gurwell, U. Menzel, Saverio Lombardi, Calvin A. Johnson, P. Kar, M. Villata, K. Mallot, R. J. García López, Felix Spanier, M. Kertzman, A. C. S. Readhead, E. Prandini, D. Galindo, Merja Tornikoski, Yusuke Konno, Diego F. Torres, M. G. Nikolashvili, D. Eisenacher, Antonio Stamerra, K. Kodani, Givi N. Kimeridze, Julian Sitarek, Lorand A. Sigua, K. Nishijima, J. V. Tucci, A. Cesarini, M. Perri, P. Kaaret, J. Storz, D. Dominis Prester, Martin Pohl, C. M. Raiteri, Markus Garczarczyk, C. Fruck, A. Sillanpää, N. Håkansson, M. Makariev, T. Toyama, L. Maraschi, A. Pichel, Jose Miguel Miranda, Matteo Cerruti, Konstancja Satalecka, J. Becerra González, P. Antoranz, Amy Furniss, S. P. Wakely, B. Jordan, Elena G. Larionova, Xuhui Chen, H. C. Lin, Geza Gyuk, Louis Antonelli, Michele Doro, Abelardo Moralejo, Jelena Aleksić, S. McArthur, M. L. Knoetig, P. G. Prada Moroni, P. Munar-Adrover, Ivica Puljak, E. Collins-Hughes, K. Meagher, Nikola Godinovic, Benito Marcote, T. Steinbring, W. Idec, M. V. Fonseca, Pierre Colin, P. Temnikov, M. Hayashida, Patrick Vogler, J. Tyler, A. Niedzwiecki, C. Schultz, V. Scapin, J. H. Buckley, P. Moriarty, Tomislav Terzić, K. Berger, T. Sakamoto, C. Delgado Mendez, S. R. Gozzini, B. McBreen, O. Tibolla, Shan Sun, E. de Oña Wilhelmi, Ivan S. Troitsky, David Paneque, I. Snidaric, Marc Ribó, P. Da Vela, D. Hildebrand, B. Steinke, Steven N. Shore, Q. Feng, K. Frantzen, Massimo Persic, Hidetoshi Kubo, A. Boller, D. A. Morozova, A. Wilhelm, R. Reinthal, Thomas Bretz, Sofia O. Kurtanidze, Kari Nilsson, Elina Lindfors, Justin D. Finke, J. Krause, B. De Lotto, Walter Max-Moerbeck, K. Saito, Razmik Mirzoyan, U. Barres de Almeida, A. González Muñoz, V. Kadenius, Damir Lelas, N. Mankuzhiyil, J. P. Finley, J. S. Perkins, Wen Ping Chen, S. Paiano, E. Lorenz, Karl Mannheim, H. Prokoph, Hanna Kellermann, Daniel Mazin, I. Lozano, Dorota Sobczyńska, J. D. Eisch, Wolfgang Rhode, Daniela Dorner, M. Palatiello, Joseph Moody, Lucy Fortson, M. I. Martínez, M. Gaug, P. Bangale, G. De Caneva, J. Herrera, Matthias Beilicke, Koji Noda, J. Millis, Abraham D. Falcone, Francesco Dazzi, Karlen Shahinyan, Elisa Bernardini, S. Bonnefoy, Sabrina Einecke, J. Rodriguez Garcia, W. Bednarek, Fabrizio Tavecchio, Ll. Font, A. C. Sadun, Anne Lähteenmäki, Stefano Covino, M. J. Lang, A. Varlotta, Masahiro Teshima, A. McCann, Ekaterina Koptelova, A. C. Rovero, J. Kushida, D. Tescaro, Jose Luis Contreras, G. Hughes, M. Uellenbeck, Takashi Saito, Y. Hanabata, A. Popkow, Juan Cortina, V. Bugaev, David Kieda, Reiko Orito, S. Buson, J. L. Richards, Ann E. Wehrle, D. Garrido Terrats, P. Fortin, Oscar Blanch, Ralph Bird, S. Archambault, Valeri M. Larionov, V. Scalzotto, Ana Babić, Julia Thaele, E. Carmona, A. De Angelis, A. Treves, R. A. Ong, G. Maneva, R. Zanin, A. N. Otte, Adrian Biland, J. Rico, Alan P. Marscher, Universitat de Barcelona, Department of Radio Science and Engineering, Aalto-yliopisto, Aalto University, and ~

Subjects
extragalactic background light, Ciencias Físicas, spectral energy-distribution, Flux, Non-thermal / galaxies, Astrophysics, law.invention, Relativistic particle, purl.org/becyt/ford/1 [https], atmospheric cherenkov telescopes, Raigs gamma, bl lacertae objects, law, MAGIC (telescope), Active / BL Lacertae objects, astro-ph.HE, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, individual: Mrk 421 [BL Lacertae objects], education.field_of_study, gamma-ray outburst, non-thermal [radiation mechanisms], BL Lacertae objects: individual: Mrk 421, Galaxies: active, Gamma rays: galaxies, Radiation mechanisms: non-thermal, Astronomy and Astrophysics, Space and Planetary Science, Particle acceleration, NON THERMAL RADIATION, large-area telescope, active [galaxies], galaxies [gamma rays], BL LACERTAE OBJECTS, Electrónica, self-compton model, Electricidad, Astrophysics - High Energy Astrophysical Phenomena, CIENCIAS NATURALES Y EXACTAS, Flare, Astrophysics::High Energy Astrophysical Phenomena, galaxies: active, Population, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Radio telescope, radiation mechanisms: non-thermal, gamma rays: galaxies, Radiation mechanisms, BL Lacertae objects: individual, simultaneous multiwavelength observations, AGN, education, Blazar, Individual: Mrk 421 / gamma rays, tev blazars, Gamma rays, Institut für Physik und Astronomie, purl.org/becyt/ford/1.3 [https], Galaxies, Astronomía, x-ray, Galàxies actives, Active galaxies, ddc:520
Abstract

A flare from the TeV blazar Mrk 421, occurring in March 2010, was observed for 13 consecutive days from radio to very high energy (VHE, E > 100 GeV) gamma-rays with MAGIC, VERITAS, Whipple, FermiLAT, MAXI, RXTE, Swift, GASP-WEBT, and several optical and radio telescopes. We model the day-scale SEDs with one-zone and two-zone synchrotron self-Compton (SSC) models, investigate the physical parameters, and evaluate whether the observed broadband SED variability can be associated to variations in the relativistic particle population. Flux variability was remarkable in the X-ray and VHE bands while it was minor or not significant in the other bands. The one-zone SSC model can describe reasonably well the SED of each day for the 13 consecutive days. This flaring activity is also very well described by a two-zone SSC model, where one zone is responsible for the quiescent emission while the other smaller zone, which is spatially separated from the first one, contributes to the daily-variable emission occurring in X-rays and VHE gamma-rays. Both the one-zone SSC and the two-zone SSC models can describe the daily SEDs via the variation of only four or five model parameters, under the hypothesis that the variability is associated mostly to the underlying particle population. This shows that the particle acceleration and cooling mechanism producing the radiating particles could be the main one responsible for the broadband SED variations during the flaring episodes in blazars. The two-zone SSC model provides a better agreement to the observed SED at the narrow peaks of the low- and high-energy bumps during the highest activity, although the reported one-zone SSC model could be further improved by the variation of the parameters related to the emitting region itself ($\delta$, $B$ and $R$), in addition to the parameters related to the particle population., Comment: Published in A&A, 30 pages, 15 figures, 6 tables. Online-data: multi-wavelength light curves (data in Fig. 1) and broadband spectral energy distributions (the data in Figs. 6, and B1-B4) are available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/578/A22. Corresponding authors: David Paneque (dpaneque@mpp.mpg.de), Shangyu Sun (sysun@mpp.mpg.de), Hajime Takami (takami@post.kek.jp)

Published
2014
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37. VERITAS Observations of the BL Lac Object PG 1553+113

Author

D. Staszak, K. Ragan, S. McArthur, E. Aliu, A. Varlotta, J. Tyler, I. Telezhinsky, J. H. Buckley, B. Zitzer, Jamie Holder, L. C. Reyes, A. Archer, Matteo Cerruti, Hugh Dickinson, Amy Furniss, L. Ciupik, David A. Williams, D. S. Hanna, J. Grube, Manel Errando, A. N. Otte, Karen Byrum, Martin Pohl, A. O'Faolain de Bhroithe, J. D. Eisch, Geza Gyuk, M. P. Connolly, H. Prokoph, S. Kumar, A. Weinstein, J. Dumm, J. V. Tucci, J. P. Finley, P. Moriarty, G. Hughes, A. McCann, K. Meagher, G. H. Gillanders, Jean-Francois Rajotte, S. P. Wakely, Vladimir Vassiliev, Wystan Benbow, K. Berger, N. Galante, E. Pueschel, T. B. Humensky, David Kieda, Henric Krawczynski, A. S Madhavan, N. Håkansson, Gordon T. Richards, E. Roache, Sinéad M. Griffin, Anna Barnacka, Frank Krennrich, Xuhui Chen, B. Behera, P. Kaaret, J. V. Cardenzana, Daniel Nieto, A. Wilhelm, R. A. Ong, M. Kertzman, A. Popkow, C. A. Johnson, Lucy Fortson, S. T. Griffiths, N. H. Park, J. Millis, Q. Feng, S. Federici, Matthias Beilicke, V. Bugaev, Wei Cui, T. Aune, P. T. Reynolds, G. H. Sembroski, R. Welsing, Matthew R. Orr, J. S. Perkins, Y. Khassen, P. Kar, P. Fortin, Ralph Bird, M. J. Lang, John L. Quinn, Abraham D. Falcone, Karlen Shahinyan, and ~

Subjects
extragalactic background light, spectra, Astrophysics::High Energy Astrophysical Phenomena, blazars, pg-1553+113, FOS: Physical sciences, Flux, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, telescope, 10. No inequality, Blazar, optical spectroscopy, bl lacertae objects: general, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Spectral index, model, Gamma rays, Institut für Physik und Astronomie, Astronomy and Astrophysics, gamma-rays, Redshift, radiation, Crab Nebula, Pair production, Extragalactic background light, Space and Planetary Science, ddc:520, lacertae objects, Astrophysics - High Energy Astrophysical Phenomena, BL Lac object
Abstract

We present results from VERITAS observations of the BL Lac object PG 1553+113 spanning the years 2010, 2011, and 2012. The time-averaged spectrum, measured between 160 and 560\,GeV, is well described by a power law with a spectral index of $4.33 \pm 0.09$. The time-averaged integral flux above $200\,$GeV measured for this period was $(1.69 \pm 0.06) \times 10^{-11} \, \mathrm{ph} \, \mathrm{cm}^{-2} \, \mathrm{s}^{-1}$, corresponding to 6.9\% of the Crab Nebula flux. We also present the combined $\gamma$-ray spectrum from the Fermi Large Area Telescope and VERITAS covering an energy range from 100~MeV to 560~GeV. The data are well fit by a power law with an exponential cutoff at $\rm {101.9 \pm 3.2 \, \mathrm{GeV}} $. The origin of the cutoff could be intrinsic to PG~1553+113 or be due to the $\gamma$-ray opacity of our universe through pair production off the extragalactic background light (EBL). Given lower limits to the redshift of $\rm z \negthinspace > \negthinspace 0.395$ based on optical/UV observations of PG~1553+113, the cutoff would be dominated by EBL absorption. Conversely, the small statistical uncertainties of the VERITAS energy spectrum have allowed us to provide a robust upper limit on the redshift of PG 1553+113 of $z \negthinspace \leq \negthinspace 0.62$. A strongly-elevated mean flux of $(2.50 \pm 0.14) \times 10^{-11} \, \mathrm{ph} \, \mathrm{cm}^{-2} \, \mathrm{s}^{-1}$ (10.3\% of the Crab Nebula flux) was observed during 2012, with the daily flux reaching as high as $(4.44 \pm 0.71) \times 10^{-11} \, \mathrm{ph} \, \mathrm{cm}^{-2} \, \mathrm{s}^{-1}$ (18.3\% of the Crab Nebula flux) on MJD 56048. The light curve measured during the 2012 observing season is marginally inconsistent with a steady flux, giving a $\chi^2$ probability for a steady flux of 0.03\%., Comment: in press in ApJ, 2014

Published
2014
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38. Constraints on very high energy emission from grb 130427a

Author

P. Kaaret, S. McArthur, Wei Cui, J. Grube, Manel Errando, Q. Feng, H. Prokoph, R. Welsing, A. McCann, Geza Gyuk, J. V. Tucci, P. Fortin, Gernot Maier, Valerie Connaughton, L. Ciupik, O. M. Weiner, G. H. Sembroski, Péter Veres, K. Berger, S. Federici, A. Popkow, H. Fleischhack, J. H. Buckley, S. P. Wakely, Xuhui Chen, H. Krawczynski, I. Telezhinsky, Jamie Holder, M. J. Lang, A. Wilhelm, David Kieda, Anna Barnacka, A. S. Madhavan, K. Ragan, P. Moriarty, J. Tyler, A. Furniss, John L. Quinn, B. Zitzer, Wystan Benbow, G. H. Gillanders, E. Pueschel, Jonathan Biteau, A. Varlotta, N. Galante, Gareth Hughes, Frank Krennrich, Y. Khassen, T. B. Humensky, Julie McEnery, M. Kertzman, Jean-Francois Rajotte, A. W. Smith, Vladimir Vassiliev, A. O'Faolain de Bhroithe, Luis C. Reyes, J. V. Cardenzana, E. Roache, Gordon T. Richards, C. A. Johnson, N. Håkansson, David A. Williams, N. H. Park, Karen Byrum, M. Beilicke, Abraham D. Falcone, Karlen Shahinyan, J. D. Eisch, A. Weinstein, P. Kar, P. T. Reynolds, S. Vincent, Daniel Nieto, J. Millis, R. Mukherjee, Lucy Fortson, D. Staszak, Matteo Cerruti, Sylvia J. Zhu, Martin Pohl, K. Meagher, R. A. Ong, D. S. Hanna, V. Bugaev, S. T. Griffiths, J. S. Perkins, A. N. Otte, E. Aliu, T. Aune, S. Griffin, Hugh Dickinson, and J. P. Finley

Subjects
spectra, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, telescope, law.invention, Telescope, swift, Spitzer Space Telescope, law, component, tev, Astrophysics::Galaxy Astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, gamma-ray bursts, Gamma ray, GRB 130427A, Institut für Physik und Astronomie, Astronomy and Astrophysics, afterglows, Cherenkov Telescope Array, Redshift, gamma-ray burst: individual (grb 130427a), mission, 13. Climate action, Space and Planetary Science, ddc:520, Astrophysics - High Energy Astrophysical Phenomena, Gamma-ray burst, limits, Fermi Gamma-ray Space Telescope
Abstract

Prompt emission from the very fluent and nearby (z=0.34) gamma-ray burst GRB 130427A was detected by several orbiting telescopes and by ground-based, wide-field-of-view optical transient monitors. Apart from the intensity and proximity of this GRB, it is exceptional due to the extremely long-lived high-energy (100 MeV to 100 GeV) gamma-ray emission, which was detected by the Large Area Telescope on the Fermi Gamma-ray Space Telescope for ~70 ks after the initial burst. The persistent, hard-spectrum, high-energy emission suggests that the highest-energy gamma rays may have been produced via synchrotron self-Compton processes though there is also evidence that the high-energy emission may instead be an extension of the synchrotron spectrum. VERITAS, a ground-based imaging atmospheric Cherenkov telescope array, began follow-up observations of GRB 130427A ~71 ks (~20 hr) after the onset of the burst. The GRB was not detected with VERITAS; however, the high elevation of the observations, coupled with the low redshift of the GRB, make VERITAS a very sensitive probe of the emission from GRB 130427A for E > 100 GeV. The non-detection and consequent upper limit derived place constraints on the synchrotron self-Compton model of high-energy gamma-ray emission from this burst., 22 pages, 4 figures, 1 table

Published
2014
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39. Spatially Resolving the very high Energy Emission from MGRO J2019+37 with VERITAS

Author

I. Telezhinsky, Jamie Holder, S. Vincent, A. Popkow, L. C. Reyes, A. Bouvier, Abraham D. Falcone, Eric V. Gotthelf, Karlen Shahinyan, Sinéad M. Griffin, P. Fortin, P. Kaaret, Jean-Francois Rajotte, Ralph Bird, T. Aune, B. Behera, Daniel Nieto, J. P. Finley, Martin Pohl, C. A. Johnson, M. Kertzman, D. Staszak, D. S. Hanna, T. B. Humensky, J. Dumm, Wystan Benbow, K. Ragan, A. O'Faolain de Bhroithe, L. Ciupik, F. Krennrich, John L. Quinn, V. Bugaev, E. Aliu, R. A. Ong, Matthias Beilicke, B. Zitzer, Oleg Kargaltsev, J. V. Tucci, S. T. Griffiths, Mallory S. E. Roberts, Gernot Maier, K. Berger, J. Grube, Manel Errando, A. McCann, Q. Feng, N. Galante, Y. Khassen, H. Prokoph, Amanda Weinstein, S. McArthur, Xuhui Chen, A. N. Otte, S. P. Wakely, M. P. Connolly, Dirk Pandel, A. W. Smith, S. Federici, A. S Madhavan, David Kieda, Henrike Fleischhack, Gordon T. Richards, E. Roache, G. H. Gillanders, Reshmi Mukherjee, G. Hughes, M. J. Lang, A. Wilhelm, Matteo Cerruti, Amy Furniss, David A. Williams, Wei Cui, P. T. Reynolds, Geza Gyuk, Vikram V. Dwarkadas, J. Tyler, Lucy Fortson, P. Moriarty, N. H. Park, J. Millis, J. H. Buckley, G. H. Sembroski, and R. Welsing

Subjects
stars, Photon, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, supernovae : individual (ctb 87), galactic plane, 01 natural sciences, Spectral line, Pulsar, pulsars : individual (psr j2021+3651), Observatory, 0103 physical sciences, pulsar wind nebula, Supernova remnant, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, cygnus region, hess, 010308 nuclear & particles physics, Star formation, Institut für Physik und Astronomie, Astronomy, Astronomy and Astrophysics, gamma-ray emission, gamma rays : stars, psr j2021+3651, milagro, Supernova, 13. Climate action, Space and Planetary Science, Milagro, ddc:520, Astrophysics - High Energy Astrophysical Phenomena, discovery, associations
Abstract

We present very high energy (VHE) imaging of MGRO J2019+37 obtained with the VERITAS observatory. The bright extended ($\sim2^{\circ}$) unidentified Milagro source is located towards the rich star formation region Cygnus-X. MGRO J2019+37 is resolved into two VERITAS sources. The faint point-like source VER J2016+371 overlaps CTB 87, a filled-center remnant (SNR) with no evidence of a supernova remnant shell at the present time. Its spectrum is well fit in the $0.65 - 10$ TeV energy range by a power-law model with photon index $2.3\pm0.4$. VER J2019+368 is a bright extended ($\sim1^{\circ}$) source, that likely accounts for the bulk of the Milagro emission and is notably coincident with PSR J2021+3651 and the star formation region Sh 2-104. Its spectrum in the range $1-30$ TeV is well fit with a power-law model of photon index $1.75\pm0.3$, among the hardest values measured in the VHE band, comparable to that observed near Vela-X. We explore the unusual spectrum and morphology in the radio and X-ray bands to constrain possible emission mechanisms for this source., 9 pages, 8 figures, accepted for publication in the Astrophysical Journal

Published
2014
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40. Investigating the TeV morpholoy of MGRO J1908+06 with veritas

Author

P. Kaaret, J. Grube, S. Archambault, M. P. Connolly, Manel Errando, J. V. Cardenzana, J. E. Ward, Wei Cui, K. Berger, John L. Quinn, M. Kertzman, J. V. Tucci, P. Fortin, A. Varlotta, Gernot Maier, E. Collins-Hughes, Frank Krennrich, A. O'Faolain de Bhroithe, S. Vincent, G. H. Sembroski, M. Beilicke, H. Prokoph, R. Mukherjee, N. Galante, S. P. Wakely, M. J. Lang, R. Welsing, D. Gall, G. Ratliff, A. Wilhelm, Q. Feng, Gareth Hughes, Martin Pohl, H. Fleischhack, R. A. Ong, Xuhui Chen, A. W. Smith, Y. Khassen, S. Federici, David Kieda, Dirk Pandel, J. Dumm, J. H. Buckley, Gordon T. Richards, T. B. Humensky, K. Meagher, S. T. Griffiths, Vikram V. Dwarkadas, K. Ragan, E. Roache, D. S. Hanna, B. Behera, Luis C. Reyes, A. Furniss, Daniel Nieto, D. Staszak, Abraham D. Falcone, Karlen Shahinyan, N. H. Park, P. T. Reynolds, Jean-Francois Rajotte, V. Bugaev, Lucy Fortson, J. P. Finley, Sunil Kumar, A. Popkow, F. Sheidaei, J. Millis, J. Tyler, A. Weinstein, P. Moriarty, S. Griffin, E. Aliu, Ralph Bird, I. Telezhinsky, Jamie Holder, A. S. Madhavan, Wystan Benbow, A. N. Otte, Geza Gyuk, Julien Rousselle, L. Ciupik, K. Tsurusaki, G. H. Gillanders, Vladimir Vassiliev, Matteo Cerruti, T. Aune, and A. McCann

Subjects
High energy, Photon, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, g40.5-0.5, Astrophysics, array, 01 natural sciences, Pulsar wind nebula, galactic plane, remnant, Pulsar, pulsars: individual (psr j1907+0602), Observatory, 0103 physical sciences, pulsar wind nebula, 010303 astronomy & astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, gamma-ray burst: individual (mgro j1908+06, ver j1907+062), 010308 nuclear & particles physics, Sigma, Institut für Physik und Astronomie, Astronomy and Astrophysics, gamma rays: general, gamma-ray emission, milagro, psr j1907+0602, 13. Climate action, Space and Planetary Science, ism: supernova remnants, ddc:520, High Energy Physics::Experiment, Astrophysics - High Energy Astrophysical Phenomena
Abstract

We report on deep observations of the extended TeV gamma-ray source MGRO J1908+06 made with the VERITAS very high energy (VHE) gamma-ray observatory. Previously, the TeV emission has been attributed to the pulsar wind nebula (PWN) of the Fermi-LAT pulsar PSR J1907+0602. We detect MGRO J1908+06 at a significance level of 14 standard deviations (14 sigma) and measure a photon index of 2.20 +/- 0.10_stat +/- 0.20_sys. The TeV emission is extended, covering the region near PSR J1907+0602 and also extending towards SNR G40.5--0.5. When fitted with a 2-dimensional Gaussian, the intrinsic extension has a standard deviation of sigma_src = 0.44 +/- 0.02 degrees. In contrast to other TeV PWNe of similar age in which the TeV spectrum softens with distance from the pulsar, the TeV spectrum measured near the pulsar location is consistent with that measured at a position near the rim of G40.5--0.5, 0.33 degrees away., To appear in ApJ, 8 pages

Published
2014
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41. Test of Models of the Cosmic Infrared Background with Multiwavelength Observations of the Blazar 1ES 1218+30.4 in 2009

Author

Wystan Benbow, Daniel Nieto, A. N. Otte, M. P. Connolly, A. Bouvier, L. Ciupik, R. Dickherber, Geza Gyuk, T. Aune, P. T. Reynolds, P. Moriarty, S. McArthur, Ralph Bird, S. Federici, J. P. Finley, J. H. Buckley, Sinéad M. Griffin, Matthias Beilicke, P. Majumdar, Lucy Fortson, N. Galante, M. J. Lang, R. A. Ong, A. Varlotta, M. Kertzman, A. S Madhavan, Markus Böttcher, A. Lamerato, Q. Feng, John L. Quinn, Gordon T. Richards, E. Roache, G. D. Şentürk, Gernot Maier, D. S. Hanna, T. C. Arlen, Wei Cui, C. Gusbar, P. Roustazadeh, G. Hughes, Vladimir Vassiliev, H. Prokoph, S. P. Wakely, R. Welsing, Matthew R. Orr, V. Bugaev, C. Skole, G. H. Gillanders, Daniel Gall, P. Kaaret, Y. Khassen, E. Collins-Hughes, A. Iii. Garson, G. Tešić, Amy Furniss, Henric Krawczynski, S. Vincent, D. B. Saxon, N. H. Park, J. Millis, K. Li, J. S. Perkins, Martin Pohl, J. Dumm, G. H. Sembroski, S. Archambault, Reshmi Mukherjee, A. Weinstein, A. D. Falcone, A. McCann, A. O'Faolain de Bhroithe, David Kieda, M. Theiling, I. Telezhinsky, Jamie Holder, David A. Williams, D. Staszak, K. Ragan, B. Zitzer, J. Grube, Manel Errando, and A. Popkow

Subjects
Smithsonian institution, Astrophysics::High Energy Astrophysical Phenomena, Cosmic background radiation, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, cosmic background radiation, timing explorer, Cosmic infrared background, gamma rays: galaxies, strong flares, Blazar, bl lacertae objects: general, Diffuse radiation, Physics, gamma-ray observations, bl lacertae objects: individual (1es1218+30.4), particle-acceleration, tev blazars, Astronomy, Institut für Physik und Astronomie, Astronomy and Astrophysics, Visible radiation, galaxies: jets, veritas observations, diffuse radiation, Red shift, large-area telescope, x-ray, Space and Planetary Science, active galactic nuclei, extragalactic magnetic-fields, ddc:520
Abstract

We present the results of a multi-wavelength campaign targeting the blazar 1ES 1218+30.4 with observations with the 1.3 m McGraw-Hill optical telescope, the Rossi X-ray Timing Explorer (RXTE), the Fermi Gamma-Ray Space Telescope, and the Very Energetic Radiation Imaging Telescope Array System (VERITAS). The RXTE and VERITAS observations were spread over a 13 day period and revealed clear evidence for flux variability, and a strong X-ray and gamma-ray flare on 2009 February 26 (MJD 54888). The campaign delivered a well-sampled broadband energy spectrum with simultaneous RXTE and VERITAS very high energy (VHE, > 100 GeV) observations, as well as contemporaneous optical and Fermi observations. The 1ES 1218+30.4 broadband energy spectrum-the first with simultaneous X-ray and VHE gamma-ray energy spectra-is of particular interest as the source is located at a high cosmological redshift for a VHE source (z = 0.182), leading to strong absorption of VHE gamma rays by photons from the optical/infrared extragalactic background light (EBL) via gamma VHE +gamma EBL -> e(+) e(-)pair-creation processes. We model the data with a one-zone synchrotron self-Compton (SSC) emission model and with the extragalactic absorption predicted by several recent EBL models. We find that the observations are consistent with the SSC scenario and all the EBL models considered in this work. We discuss observational and theoretical avenues to improve on the EBL constraints.

Published
2014
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42. Observation of Markarian 421 in TeV gamma rays over a 14-year time span

Author

M. J. Lang, J. Tyler, J. H. Buckley, D. A. Carter-Lewis, E. Collins-Hughes, G. H. Gillanders, S. P. Wakely, Daniel Gall, L. Ciupik, N. Galante, E. Roache, A. N. Otte, H. Krawczynski, T. Reynolds, M. P. Connolly, D. S. Hanna, Ralph Bird, G. Finnegan, Geza Gyuk, K. Ragan, A. W. Smith, C. Duke, A. Pichel, G. H. Sembroski, Lucy Fortson, R. Welsing, Abraham D. Falcone, T. C. Arlen, V. Bugaev, Matthew R. Orr, J. P. Finley, Wei Cui, Y. Khassen, V. A. Acciari, T. Aune, T. C. Weekes, S. M. Bradbury, John Toner, A. C. Rovero, A. Cesarini, A. S. Madhavan, Wystan Benbow, Martin Pohl, John L. Quinn, P. Moriarty, R. A. Ong, K. G. Gibbs, J. Dumm, J. S. Perkins, S. J. Fegan, S. Federici, A. Weinstein, Stephanie Wissel, M. Schroedter, I. de la Calle Perez, A. Varlotta, A. Bouvier, P. Kaaret, J. E. Ward, David Kieda, M. Theiling, Sinéad M. Griffin, M. Kertzman, A. O'Faolain de Bhroithe, D. J. Fegan, T. J. N. Nelson, J. A. Gaidos, David A. Williams, I. Telezhinsky, T. B. Humensky, Julie McEnery, D. Horan, D. Petry, J. Grube, M. Vivier, and F. Krennrich

Subjects
multiwavelength observations, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Active galactic nucleus, Ciencias Físicas, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Flux, Astrophysics, telescope, timing explorer, 01 natural sciences, Spectral line, law.invention, purl.org/becyt/ford/1 [https], Telescope, law, blazar markarian-421, emission, 0103 physical sciences, crab-nebula, flare, AGN, Blazar, tev gamma rays, 010303 astronomy & astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Markarian 421, 010308 nuclear & particles physics, markarian 421, Gamma ray, Astronomy, Institut für Physik und Astronomie, Astronomy and Astrophysics, purl.org/becyt/ford/1.3 [https], TeV gamma rays, Astronomía, Crab Nebula, correlated variability, active galactic nuclei, ddc:540, agn, Astrophysics - High Energy Astrophysical Phenomena, Markarian galaxies, CIENCIAS NATURALES Y EXACTAS, energy, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract

The variability of the blazar Markarian 421 in TeV gamma rays over a 14-year time period has been explored with the Whipple 10 m telescope. It is shown that the dynamic range of its flux variations is large and similar to that in X-rays. A correlation between the X-ray and TeV energy bands is observed during some bright flares and when the complete data sets are binned on long timescales. The main database consists of 878.4 hours of observation with the Whipple telescope, spread over 783 nights. The peak energy response of the telescope was 400 GeV with 20% uncertainty. This is the largest database of any TeV-emitting active galactic nucleus (AGN) and hence was used to explore the variability profile of Markarian 421. The time-averaged flux from Markarian 421 over this period was 0.446$\pm$0.008 Crab flux units. The flux exceeded 10 Crab flux units on three separate occasions. For the 2000-2001 season the average flux reached 1.86 Crab units, while in the 1996-1997 season the average flux was only 0.23 Crab units., Comment: 29 pages, 15 figures. Accepted for publication in Astroparticle Physics

Published
2014
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43. A Three-Year Multi-Wavelength Study of the Very-High-Energy $\gamma$-Ray Blazar 1ES 0229+200

Author

F. Krennrich, A. McCann, A. Popkow, E. Aliu, M. Theiling, T. Aune, B. Zitzer, J. S. Perkins, J. H. Buckley, Wystan Benbow, V. V. Vassiliev, Manel Errando, A. O'Faolain de Bhroithe, A. Varlotta, K. Meagher, D. B. Kieda, P. Fortin, A. N. Otte, Anna Zajczyk, J. P. Dumm, Henrike Fleischhack, M. P. Connolly, John L. Quinn, Matthias Beilicke, S. Federici, Ralph Bird, P. Moriarty, Nicola Galante, J. Grube, I. Telezhinsky, Gernot Maier, J. P. Finley, B. Behera, Daniel Nieto, L. Ciupik, T. C. Weekes, Jamie Holder, Nahee Park, Xuhui Chen, K. L. Byrum, H. Prokoph, R. A. Ong, Y. Khassen, L. C. Reyes, S. McArthur, S. T. Griffiths, S. Archambault, Reshmi Mukherjee, J. Millis, S. P. Wakely, Wei Cui, V. Bugaev, D. Staszak, K. Ragan, A. W. Smith, D. S. Hanna, A. S Madhavan, C. Duke, Gordon T. Richards, T. C. Arlen, E. Roache, P. Kaaret, P. T. Reynolds, David A. Williams, R. Welsing, C. A. Johnson, Lucy Fortson, S. Vincent, Henric Krawczynski, A. J.R. Weinstein, M. J. Lang, Martin Pohl, G. H. Sembroski, A. D. Falcone, Q. Feng, T. B. Humensky, K. Berger, Matteo Cerruti, Amy Furniss, Sinéad M. Griffin, Gareth Hughes, M. Kertzman, A. Bouvier, Geza Gyuk, Pratik Majumdar, and G. H. Gillanders

Subjects
extragalactic background light, bl lacertae objects: individual (1es 0229+200, ver j0232+202), Active galactic nucleus, Astrophysics::High Energy Astrophysical Phenomena, galaxies: active, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, magnetic fields, 01 natural sciences, bl lacertae objects, 0103 physical sciences, intergalactic magnetic-field, Blazar, 010303 astronomy & astrophysics, bl lacertae objects: general, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, space-telescope, distant blazars, tev blazars, 010308 nuclear & particles physics, Institut für Physik und Astronomie, Astronomy and Astrophysics, gamma rays: general, diffuse radiation, large-area telescope, Crab Nebula, x-ray, Extragalactic background light, Space and Planetary Science, active galactic nuclei, Spectral energy distribution, Intergalactic travel, ddc:520, Astrophysics - High Energy Astrophysical Phenomena, lorentz factor, Fermi Gamma-ray Space Telescope, BL Lac object
Abstract

The high-frequency-peaked BL Lacertae object 1ES 0229+200 is a relatively distant (z = 0.1396), hard-spectrum (Gamma ~ 2.5), very-high-energy-emitting (E > 100 GeV) gamma-ray blazar. Very-high-energy measurements of this active galactic nucleus have been used to place constraints on the intensity of the extragalactic background light and the intergalactic magnetic field. A multi-wavelength study of this object centered around very-high-energy observations by VERITAS is presented. This study obtained, over a period of three years, an 11.7 standard deviation detection and an average integral flux F(E>300 GeV) = (23.3 +- 2.8_stat +- 5.8_sys) x 10^-9 photons m^-2 s^-1, or 1.7% of the Crab Nebula's flux (assuming the Crab Nebula spectrum measured by H.E.S.S). Supporting observations from Swift and RXTE are analyzed. The Swift observations are combined with previously published Fermi observations and the very-high-energy measurements to produce an overall spectral energy distribution which is then modeled assuming one-zone synchrotron-self-Compton emission. The chi^2 probability of the TeV flux being constant is 1.6%. This, when considered in combination with measured variability in the X-ray band, and the demonstrated variability of many TeV blazars, suggests that the use of blazars such as 1ES 0229+200 for intergalactic magnetic field studies may not be straightforward and challenges models that attribute hard TeV spectra to secondary gamma-ray production along the line of sight., Accepted for publication in ApJ

Published
2014
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44. Cutoff in the T[CLC]e[/CLC]V Energy Spectrum of Markarian 421 during Strong Flares in 2001

Author

H. J. Rose, M. Catanese, M. J. Lang, J. A. Gaidos, I. H. Bond, G. H. Sembroski, J. P. Finley, I. de la Calle Perez, R. A. Ong, John Kildea, T. C. Weekes, B. McKernan, S. LeBohec, S. Dunlea, M. Kertzman, R. Pallassini, A. M. Hillas, R. Sidwell, M. Jordan, Frank Krennrich, J. Knapp, Wei Cui, S. P. Swordy, Dietrich Müller, K. Kosack, N. W. Reay, S. M. Bradbury, Jamie Holder, P. Moriarty, D. A. Carter-Lewis, N. Stanton, H. M. Badran, P. T. Reynolds, Tony Hall, J. H. Buckley, S. P. Wakely, David Kieda, John L. Quinn, K. G. Gibbs, D. J. Fegan, D. Das, Vladimir Vassiliev, D. Horan, S. J. Fegan, D. Petry, and G. H. Gillanders

Subjects
Long lasting, mkn-501, Astrophysics::High Energy Astrophysical Phenomena, hegra, Astrophysics, Power law, objects, blazar, jet, Energy spectrum, Statistical precision, photons, Cutoff, gamma rays : observations, Blazar, Background radiation, Physics, active galaxy markarian-421, Astronomy and Astrophysics, gamma-rays, acceleration, Space and Planetary Science, Spectral energy distribution, High Energy Physics::Experiment, bl lacertae objects : individual (markarian 421), cherenkov telescope system
Abstract

Exceptionally strong and long lasting flaring activity of the blazar Markarian 421 (Mrk 421) occurred between January and March 2001. Based on the excellent signal-to-noise ratio of the data we derive the energy spectrum between 260 GeV - 17 TeV with unprecedented statistical precision. The spectrum is not well described by a simple power law even with a curvature term. Instead the data can be described by a power law with exponential cutoff: $\rm {{dN}\over{dE}} \propto \rm E^{-2.14 \pm 0.03_{stat}} \times e^{-E/E_{0}} m^{-2} s^{-1} TeV^{-1}$ with $\rm E_{0} = 4.3 \pm 0.3_{stat} TeV$. Mrk 421 is the second $\gamma$-ray blazar that unambiguously exhibits an absorption-like feature in its spectral energy distribution at 3-6 TeV suggesting that this may be a universal phenomenon, possibly due to the extragalactic infra-red background radiation.

Published
2001
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45. Discovery of TeV Gamma-ray Emission Toward Supernova Remnant SNR G78.2+2.1

Author

M. Kertzman, A. O'Faolain de Bhroithe, M. Schroedter, Vikram V. Dwarkadas, S. Vincent, Wei Cui, M. J. Lang, S. Thibadeau, A. N. Otte, M. P. Connolly, A. McCann, R. Mukherjee, D. B. Saxon, N. H. Park, J. Millis, T. Aune, J. E. Ward, A. Cesarini, P. Moriarty, John L. Quinn, T. B. Humensky, A. Furniss, Frank Krennrich, A. S. Madhavan, G. Tešić, Gernot Maier, H. Prokoph, A. Varlotta, Wystan Benbow, S. P. Wakely, Eric V. Gotthelf, E. Roache, J. P. Finley, S. Archambault, H. J. Rose, R. A. Ong, Ralph Bird, G. H. Sembroski, P. Kaaret, Amanda Weinstein, Abraham D. Falcone, R. Welsing, Vladimir Vassiliev, L. Ciupik, T. C. Weekes, J. Grube, D. Gall, Geza Gyuk, K. Tsurusaki, S. Federici, Manel Errando, T. C. Arlen, J. H. Buckley, G. H. Gillanders, P. Majumdar, T. J. N. Nelson, S. McArthur, N. Galante, S. Godambe, Dirk Pandel, S. Griffin, G. Finnegan, C. Skole, C. Duke, David A. Williams, N. Karlsson, G. D. Şentürk, T. Weisgarber, H. Huan, E. Aliu, I. Telezhinsky, K. Lee, Jamie Holder, A. Popkow, J. Tyler, A. Bouvier, D. S. Hanna, V. Bugaev, J. S. Perkins, Martin Pohl, Q. Feng, J. Dumm, P. T. Reynolds, David Kieda, M. Theiling, Lucy Fortson, Karen Byrum, S. M. Bradbury, A. Cannon, E. Collins-Hughes, H. Krawczynski, M. Beilicke, M. Orr, G. Hughes, K. Ragan, B. Zitzer, J. Ruppel, R. Dickherber, Y. Khassen, and Luis C. Reyes

Subjects
catalog, Astrophysics::High Energy Astrophysical Phenomena, Hadron, Flux, FOS: Physical sciences, Cosmic ray, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, cosmic rays, Observatory, 0103 physical sciences, origin, Supernova remnant, 010303 astronomy & astrophysics, 2cg078+2, Astrophysics::Galaxy Astrophysics, acceleration of particles, Physics, search, High Energy Astrophysical Phenomena (astro-ph.HE), particle-acceleration, 010308 nuclear & particles physics, hess, Gamma ray, Institut für Physik und Astronomie, counterpart, Astronomy and Astrophysics, gamma rays: general, Particle acceleration, Crab Nebula, Space and Planetary Science, ism: supernova remnants, ddc:520, High Energy Physics::Experiment, Astrophysics - High Energy Astrophysical Phenomena, fermi
Abstract

We report the discovery of an unidentified, extended source of very-high-energy (VHE) gamma-ray emission, VER J2019+407, within the radio shell of the supernova remnant SNR G78.2+2.1, using 21.4 hours of data taken by the VERITAS gamma-ray observatory in 2009. These data confirm the preliminary indications of gamma-ray emission previously seen in a two-year (2007-2009) blind survey of the Cygnus region by VERITAS. VER J2019+407, which is detected at a post-trials significance of 7.5 standard deviations in the 2009 data, is localized to the northwestern rim of the remnant in a region of enhanced radio and X-ray emission. It has an intrinsic extent of 0.23^{\circ} \pm 0.03^{\circ} (stat)+0.04^{\circ}_{-0.02}^{\circ}(sys) and its spectrum is well-characterized by a differential power law (dN/dE = N_0 \times (E/TeV)^{-\Gamma}) with a photon index of {\Gamma} = 2.37 \pm 0.14 (stat) \pm 0.20 (sys) and a flux normalization of N0 = 1.5 \pm 0.2 (stat) \pm 0.4(sys) \times 10^-12 ph TeV^{-1} cm^{-2} s^{-1}. This yields an integral flux of 5.2 \pm 0.8 (stat) \pm 1.4 (sys) \times 10^-12 ph cm^{-2} s^{-1} above 320 GeV, corresponding to 3.7% of the Crab Nebula flux. We consider the relationship of the TeV gamma-ray emission with the GeV gamma-ray emission seen from SNR G78.2+2.1 as well as that seen from a nearby cocoon of freshly accelerated cosmic rays. Multiple scenarios are considered as possible origins for the TeV gamma-ray emission, including hadronic particle acceleration at the supernova remnant shock., Comment: 18 pages, 5 figures, accepted for publication in ApJ

Published
2013
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46. VERITAS Observations of the Microquasar Cygnus X-3

Author

A. Varlotta, Martin Pohl, J. S. Perkins, David Kieda, P. Moriarty, Nicola Galante, J. Grube, M. P. Connolly, David A. Williams, M. J. Lang, Xuhui Chen, Matthias Beilicke, Abraham D. Falcone, I. Telezhinsky, A. McCann, G. H. Sembroski, Daniel Nieto, Wei Cui, Q. Feng, A. O'Faolain de Bhroithe, G. H. Gillanders, Jamie Holder, Y. Khassen, H. Prokoph, Henric Krawczynski, A. J.R. Weinstein, D. S. Hanna, F. Sheidaei, K. Berger, Geza Gyuk, T. B. Humensky, L. C. Reyes, Karen Byrum, P. T. Reynolds, Pratik Majumdar, Sinéad M. Griffin, D. Staszak, K. Ragan, Matteo Cerruti, Gareth Hughes, M. Kertzman, B. Zitzer, Lucy Fortson, R. A. Ong, Amy Furniss, S. Vincent, A. W. Smith, A. S Madhavan, Ralph Bird, C. Duke, Gordon T. Richards, Manel Errando, E. Roache, S. Federici, S. T. Griffiths, Michael L. McCollough, A. Bouvier, P. Kaaret, Wystan Benbow, S. McArthur, S. Archambault, Reshmi Mukherjee, A. Popkow, A. N. Otte, V. Bugaev, John L. Quinn, N. H. Park, J. V. Tucci, Gernot Maier, J. P. Finley, S. P. Wakely, T. C. Weekes, D. Pandel, L. Ciupik, Jean-Francois Rajotte, J. Tyler, J. H. Buckley, J. P. Dumm, and M. Theiling

Subjects
Astrophysics::High Energy Astrophysical Phenomena, Radiation imaging, FOS: Physical sciences, Astrophysics, gamma rays: stars, 01 natural sciences, law.invention, Telescope, x-rays: individual (cygnus x-3), law, 0103 physical sciences, cyg x-3, 010303 astronomy & astrophysics, acceleration of particles, Physics, search, High Energy Astrophysical Phenomena (astro-ph.HE), binaries: close, 010308 nuclear & particles physics, Gamma ray, Institut für Physik und Astronomie, Astronomy and Astrophysics, gamma-ray emission, large-area telescope, scattering halo, x-ray, mission, Space and Planetary Science, cherenkov telescopes, ddc:520, relativistic jet, Astrophysics - High Energy Astrophysical Phenomena, constraints
Abstract

We report results from TeV gamma-ray observations of the microquasar Cygnus X-3. The observations were made with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) over a time period from 2007 June 11 to 2011 November 28. VERITAS is most sensitive to gamma rays at energies between 85 GeV to 30 TeV. The effective exposure time amounts to a total of about 44 hours, with the observations covering six distinct radio/X-ray states of the object. No significant TeV gamma-ray emission was detected in any of the states, nor with all observations combined. The lack of a positive signal, especially in the states where GeV gamma rays were detected, places constraints on TeV gamma-ray production in Cygnus X-3. We discuss the implications of the results., Comment: 23 pages, 4 figures, 3 tables, accepted for publication in ApJ

Published
2013
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47. MULTIWAVELENGTH OBSERVATIONS OF THE TeV BINARY LS I +61° 303 WITH VERITAS, Fermi -LAT, AND Swift /XRT DURING A TeV OUTBURST

Author

S. Archambault, Gernot Maier, A. McCann, R. A. Ong, P. T. Reynolds, Lucy Fortson, N. Galante, S. P. Wakely, J. P. Finley, P. Fortin, A. D. Falcone, S. T. Griffiths, Y. Khassen, T. C. Weekes, A. W. Smith, Martin Pohl, Gordon T. Richards, Geza Gyuk, M. J. Lang, J. Dumm, M. Beilicke, S. Griffin, A. N. Otte, P. Majumdar, M. P. Connolly, K. Berger, L. Ciupik, B. Behera, D. Staszak, N. H. Park, Wystan Benbow, D. S. Hanna, John L. Quinn, G. H. Gillanders, Matteo Cerruti, E. Aliu, C. Skole, V. Bugaev, A. Varlotta, S. Federici, Q. Feng, A. Furniss, J. S. Perkins, David Kieda, G. Ratliff, S. Vincent, P. Kaaret, Gareth Hughes, E. Roache, R. Mukherjee, I. Telezhinsky, P. Moriarty, Jamie Holder, Ralph Bird, M. Kertzman, Xuhui Chen, J. Grube, A. O'Faolain de Bhroithe, A. Weinstein, A. Bouvier, Frank Krennrich, S. McArthur, F. Sheidaei, Wei Cui, H. Prokoph, T. B. Humensky, A. Popkow, Anna Zajczyk, J. Tyler, K. Ragan, B. Zitzer, Jean-Francois Rajotte, G. H. Sembroski, and R. Welsing

Subjects
Swift, Astrophysics::High Energy Astrophysical Phenomena, Binary number, FOS: Physical sciences, Astrophysics, telescope, gamma rays: stars, 01 natural sciences, law.invention, spectrum, Telescope, star, law, gamma-ray binary, 0103 physical sciences, emission, +61-degrees-303, 010303 astronomy & astrophysics, computer.programming_language, acceleration of particles, relativistic processes, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), 010308 nuclear & particles physics, Astronomy and Astrophysics, binaries: general, x-ray, Space and Planetary Science, x-rays: binaries, Spectral energy distribution, ddc:520, Satellite, High Energy Physics::Experiment, Astrophysics - High Energy Astrophysical Phenomena, computer, Fermi Gamma-ray Space Telescope
Abstract

We present the results of a multiwavelength observational campaign on the TeV binary system LS I +61 303 with the VERITAS telescope array (>200 GeV), Fermi-LAT (0.3-300 GeV), and Swift-XRT (2-10 keV). The data were taken from December 2011 through January 2012 and show a strong detection in all three wavebands. During this period VERITAS obtained 24.9 hours of quality selected livetime data in which LS I +61 303 was detected at a statistical sig- nificance of 11.9 sigma. These TeV observations show evidence for nightly variability in the TeV regime at a post-trial significance of 3.6 sigma. The combination of the simultaneously obtained TeV and X-ray fluxes do not demonstrate any evidence for a correlation between emission in the two bands. For the first time since the launch of the Fermi satellite in 2008, this TeV detection allows the construction of a detailed MeV-TeV spectral energy distribution from LS I +61 303. This spectrum shows a distinct cutoff in emission near 4 GeV, with emission seen by the VERITAS observations following a simple power-law above 200 GeV. This feature in the spectrum of LS I +61 303, obtained from overlapping observations with Fermi-LAT and VERITAS, may indicate that there are two distinct populations of accelerated particles producing the GeV and TeV emission., Accepted for Publication in ApJ

Published
2013
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48. Discovery of TeV Gamma-ray Emission from CTA 1 by VERITAS

Author

A. N. Otte, G. H. Sembroski, M. P. Connolly, E. Aliu, T. J. N. Nelson, R. Welsing, K. Lee, L. Ciupik, M. Theiling, P. Moriarty, Eric V. Gotthelf, Geza Gyuk, N. Karlsson, J. P. Finley, Wei Cui, Q. Feng, Gernot Maier, T. C. Weekes, I. Telezhinsky, Jamie Holder, S. Thibadeau, D. Gall, Oleg Kargaltsev, A. O'Faolain de Bhroithe, H. Krawczynski, A. Furniss, N. Galante, S. P. Wakely, R. Mukherjee, R. A. Ong, E. Roache, R. Dickherber, H. Prokoph, S. Vincent, A. S. Madhavan, Wystan Benbow, Abraham D. Falcone, S. Griffin, G. Finnegan, A. W. Smith, Mallory S. E. Roberts, S. McArthur, C. Duke, B. Zitzer, P. T. Reynolds, P. Kaaret, K. Ragan, J. Tyler, F. Krennrich, Y. Khassen, M. Schroedter, A. Bouvier, Vikram V. Dwarkadas, M. Vivier, J. Grube, M. Beilicke, Manel Errando, D. Staszak, S. Federici, J. H. Buckley, P. Majumdar, J. S. Perkins, David Kieda, D. B. Saxon, E. Collins-Hughes, Luis C. Reyes, N. H. Park, David A. Williams, Patrick Slane, M. Orr, T. B. Humensky, T. Aune, S. Godambe, G. Hughes, T. Arlen, Lucy Fortson, A. Cesarini, John L. Quinn, Martin Pohl, J. Dumm, Vladimir Vassiliev, A. Varlotta, M. J. Lang, A. Weinstein, K. Tsurusaki, G. H. Gillanders, D. S. Hanna, G. Tešić, V. Bugaev, S. Archambault, and A. McCann

Subjects
catalog, gamma-rays: stars, Photon, Astrophysics::High Energy Astrophysical Phenomena, supernova remnant cta-1, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Pulsar wind nebula, atmospheric cherenkov telescopes, Pulsar, Observatory, hess j1825-137, evolution, 0103 physical sciences, pulsations, crab-nebula, Supernova remnant, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Spectral index, pulsars: individual (psr j0007+7303), 010308 nuclear & particles physics, Gamma ray, Astronomy and Astrophysics, x-rays: individual (rx j0007.0+7303), astronomy, supernovae: individual (g119.5+10.2), x-ray, Space and Planetary Science, ddc:520, High Energy Physics::Experiment, Astrophysics - High Energy Astrophysical Phenomena, pulsar-wind nebulae, Fermi Gamma-ray Space Telescope
Abstract

We report the discovery of TeV gamma-ray emission coincident with the shell-type radio supernova remnant (SNR) CTA 1 using the VERITAS gamma-ray observatory. The source, VER J0006+729, was detected as a 6.5 standard deviation excess over background and shows an extended morphology, approximated by a two-dimensional Gaussian of semi-major (semi-minor) axis 0.30 degree (0.24 degree) and a centroid 5' from the Fermi gamma-ray pulsar PSR J0007+7303 and its X-ray pulsar wind nebula (PWN). The photon spectrum is well described by a power-law dN/dE = N_0 (E/3 TeV)^(-\Gamma), with a differential spectral index of \Gamma = 2.2 +- 0.2_stat +- 0.3_sys, and normalization N_0 = (9.1 +- 1.3_stat +- 1.7_sys) x 10^(-14) cm^(-2) s^(-1) TeV^(-1). The integral flux, F_\gamma = 4.0 x 10^(-12) erg cm^(-2) s^(-1) above 1 TeV, corresponds to 0.2% of the pulsar spin-down power at 1.4 kpc. The energetics, co-location with the SNR, and the relatively small extent of the TeV emission strongly argue for the PWN origin of the TeV photons. We consider the origin of the TeV emission in CTA 1., Comment: 10 pages, 9 figures, accepted for publication in ApJ

Published
2012
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49. Search for a correlation between very-high-energy gamma rays and giant radio pulses in the Crab pulsar

Author

Matthias Beilicke, J. P. Dumm, Martin Pohl, G. Tešić, Q. Feng, V. Bugaev, T. Aune, A. Varlotta, R. Dickherber, T. B. Humensky, T. J. N. Nelson, S. Thibadeau, A. McCann, M. P. Connolly, Maxim Lyutikov, R. G. Wagner, Henric Krawczynski, E. Aliu, A. J.R. Weinstein, I. Telezhinsky, Jamie Holder, F. Krennrich, H. Prokoph, S. Vincent, L. C. Reyes, K. Lee, Sinéad M. Griffin, D. B. Saxon, Karen Byrum, D. S. Hanna, N. H. Park, Lucy Fortson, D. Staszak, K. Tsurusaki, M. Theiling, T. C. Arlen, K. Ragan, Gareth Hughes, Amy Furniss, P. Kaaret, M. Schroedter, B. Zitzer, E. Collins-Hughes, Gernot Maier, M. J. Lang, G. H. Gillanders, S. Godambe, S. P. Wakely, G. H. Sembroski, Daniel Gall, R. Welsing, A. N. Otte, Matthew R. Orr, L. Ciupik, A. Cesarini, R. A. Ong, V. Kondratiev, David A. Williams, John L. Quinn, A. Bouvier, J. H. Buckley, A. D. Falcone, J. P. Finley, M. Vivier, T. C. Weekes, S. LeBohec, David Kieda, S. McArthur, Y. Khassen, P. T. Reynolds, Geza Gyuk, Pratik Majumdar, S. Archambault, Reshmi Mukherjee, Wystan Benbow, J. S. Perkins, P. Moriarty, Nicola Galante, J. Grube, N. Karlsson, G. Finnegan, A. W. Smith, A. S Madhavan, C. Duke, E. Roache, G. D. Şentürk, H. Huan, A. O'Faolain de Bhroithe, S. Federici, and Wei Cui

Subjects
High energy, nebula, pulsars: individual: b0531+21, Flux, FOS: Physical sciences, Astrophysics, 01 natural sciences, Arrival time, law.invention, Radio telescope, Telescope, law, Time windows, 0103 physical sciences, emission, photons, rays: stars, geminga, 010303 astronomy & astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), model, 010308 nuclear & particles physics, Crab Pulsar, Gamma ray, Institut für Physik und Astronomie, Astronomy and Astrophysics, telescopes, universe, Space and Planetary Science, range, Astrophysics - High Energy Astrophysical Phenomena
Abstract

We present the results of a joint observational campaign between the Green Bank radio telescope and the VERITAS gamma-ray telescope, which searched for a correlation between the emission of very-high-energy (VHE) gamma rays ($E_{\gamma} >$ 150 GeV) and Giant Radio Pulses (GRPs) from the Crab pulsar at 8.9 GHz. A total of 15366 GRPs were recorded during 11.6 hours of simultaneous observations, which were made across four nights in December 2008 and in November and December 2009. We searched for an enhancement of the pulsed gamma-ray emission within time windows placed around the arrival time of the GRP events. In total, 8 different time windows with durations ranging from 0.033 ms to 72 s were positioned at three different locations relative to the GRP to search for enhanced gamma-ray emission which lagged, led, or was concurrent with, the GRP event. Further, we performed separate searches on main pulse GRPs and interpulse GRPs and on the most energetic GRPs in our data sample. No significant enhancement of pulsed VHE emission was found in any of the preformed searches. We set upper limits of 5-10 times the average VHE flux of the Crab pulsar on the flux simultaneous with interpulse GRPs on single-rotation-period time scales. On $\sim$8-second time scales around interpulse GRPs, we set an upper limit of 2-3 times the average VHE flux. Within the framework of recent models for pulsed VHE emission from the Crab pulsar, the expected VHE-GRP emission correlations are below the derived limits., Comment: 12 pages, 12 figures, To appear in The Astrophysical Journal

Published
2012
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50. A search for a geomagnetic effect on the sensitivity of the atmospheric Cherenkov imaging technique

Author

M. F. Cawley, R. C. Lamb, D. J. Fegan, D. A. Lewis, M. Chantell, Carl W. Akerlof, D. I. Meyer, G. H. Gillanders, T. C. Weekes, A. M. Hillas, and M. J. Lang

Subjects
Physics, Nuclear and High Energy Physics, Optics, Crab Nebula, Earth's magnetic field, business.industry, Astrophysics::High Energy Astrophysical Phenomena, Transverse field, Imaging technique, Astrophysics, Sensitivity (control systems), business, Cherenkov radiation
Abstract

We have searched the Whipple 1988-89 canonical Crab Nebula database for evidence of a possible geomagnetic field effect on the sensitivity of the atmospheric Cherenkov imaging technique. At the present sensitivity of the imaging technique, the selection of gamma-ray-like events on the basis of image characteristics appears to be unaffected by the transverse field strength. We are unable to detect any broadening of shower images or any increase in integrated light content.

Published
1994
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