Author: "Archambault, S." - Searchworks@Jio Institute Digital Library Search Results

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407 results on '"Archambault, S."'

1. Modeling the refractive index profile n(z) of polar ice for ultra-high energy neutrino experiments

Author: Ali, S., Allison, P., Archambault, S., Beatty, J. J., Besson, D. Z., Bishop, A., Chen, P., Chen, Y. C., Clark, B. A., Clay, W., Connolly, A., Couberly, K., Cremonesi, L., Cummings, A., Dasgupta, P., Debolt, R., de Kockere, S., de Vries, K. D., Deaconu, C., DuVernois, M. A., Flaherty, J., Friedman, E., Gaior, R., Giri, P., Hanson, J., Harty, N., Hoffman, K. D., Huang, J. J., Huang, M. -H., Hughes, K., Ishihara, A., Karle, A., Kelley, J. L., Kim, K. -C., Kim, M. -C., Kravchenko, I., Krebs, R., Kuo, C. Y., Kurusu, K., Latif, U. A., Liu, C. H, Liu, T. C., Luszczak, W., Mase, K., Muzio, M. S., Nam, J., Nichol, R. J., Novikov, A., Nozdrina, A., Oberla, E., Pan, Y., Pfendner, C., Punsuebsay, N., Roth, J., Salcedo-Gomez, A., Seckel, D., Seikh, M. F. H., Shaio, Y. -S., Smith, D., Toscano, S., Torres, J., Touart, J., van Eijndhoven, N., Vieregg, A., Wang, M. -Z., Wang, S. -H., Wissel, S. A., Xie, C., Yoshida, S., and Young, R.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: We develop an in-situ index of refraction profile using the transit time of radio signals broadcast from an englacial transmitter to 2-5 km distant radio-frequency receivers, deployed at depths up to 200 m. Maxwell's equations generally admit two ray propagation solutions from a given transmitter, corresponding to a direct path (D) and a refracted path (R); the measured D vs. R (dt(D,R)) timing differences provide constraints on the index of refraction profile near South Pole, where the Askaryan Radio Array (ARA) neutrino observatory is located. We constrain the refractive index profile by simulating D and R ray paths via ray tracing and comparing those to measured dt(D,R) signals. Using previous ice density data as a proxy for n(z), we demonstrate that our data strongly favors a glaciologically-motivated three-phase densification model rather than a single exponential scale height model. Simulations show that the single exponential model overestimates ARA neutrino sensitivity compared to the three-phase model.
Published: 2024

2. Calibration and Physics with ARA Station 1: A Unique Askaryan Radio Array Detector

Author: Seikh, M. F. H, Besson, D. Z., Ali, S., Allison, P., Archambault, S., Beatty, J. J., Bishop, A., Chen, P., Chen, Y. C., Clark, B. A., Clay, W., Connolly, A., Couberly, K., Cremonesi, L., Cummings, A., Dasgupta, P., Debolt, R., De Kockere, S., de Vries, K. D., Deaconu, C., DuVernois, M. A., Flaherty, J., Friedman, E., Gaior, R., Giri, P., Hanson, J., Harty, N., Hendricks, B., Hoffman, K. D., Huang, J. J., Huang, M. H. A., Hughes, K., Ishihara, A., Karle, A., Kelley, J. L., Kim, K. C., Kim, M. C., Kravchenko, I., Krebs, R., Kuo, C. Y., Kurusu, K., Latif, U. A., Liu, C. H., Liu, T. C., Luszczak, W., Mase, K., Muzio, M. S., Nam, J., Nichol, R. J., Novikov, A., Nozdrina, A., Oberla, E., Pan, Y., Pfendner, C., Punsuebsay, N., Roth, J., Salcedo-Gomez, A., Seckel, D., Seikh, M. F. H., Shiao, Y. S., Smith, D. J. B., Toscano, S., Torres, J., Touart, J., van Eijndhoven, N., Varner, G. S., Vieregg, A., Wang, M. Z., Wang, S. H., Wissel, S. A., Xie, C., Yoshida, S., and Young, R.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Physics - Instrumentation and Detectors
Abstract: The Askaryan Radio Array Station 1 (A1), the first among five autonomous stations deployed for the ARA experiment at the South Pole, is a unique ultra-high energy neutrino (UHEN) detector based on the Askaryan effect that uses Antarctic ice as the detector medium. Its 16 radio antennas (distributed across 4 strings, each with 2 Vertically Polarized (VPol), 2 Horizontally Polarized (HPol) receivers), and 2 strings of transmitting antennas (calibration pulsers, CPs), each with 1 VPol and 1 HPol channel, are deployed at depths less than 100 m within the shallow firn zone of the 2.8 km thick South Pole (SP) ice. We apply different methods to calibrate its Ice Ray Sampler second generation (IRS2) chip for timing offset and ADC-to-Voltage conversion factors using a known continuous wave input signal to the digitizer, and achieve a precision of sub-nanoseconds. We achieve better calibration for odd, compared to even samples, and also find that the HPols under-perform relative to the VPol channels. Our timing calibrated data is subsequently used to calibrate the ADC-to-Voltage conversion as well as precise antenna locations, as a precursor to vertex reconstruction. The calibrated data will then be analyzed for UHEN signals in the final step of data compression. The ability of A1 to scan the firn region of SP ice sheet will contribute greatly towards a 5-station analysis and will inform the design of the planned IceCube Gen-2 radio array., Comment: 10 pages
Published: 2023
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3. Triboelectric backgrounds to radio-based polar ultra-high energy neutrino (UHEN) experiments

Author: Aguilar, JA, Anker, A, Allison, P, Archambault, S, Baldi, P, Barwick, SW, Beatty, JJ, Beise, J, Besson, D, Bishop, A, Bondarev, E, Botner, O, Bouma, S, Buitink, S, Cataldo, M, Chen, CC, Chen, CH, Chen, P, Chen, YC, Choi, T, Clark, BA, Clay, W, Curtis-Ginsberg, Z, Connolly, A, Cremonesi, L, Dasgupta, P, Davies, J, de Kockere, S, de Vries, KD, Deaconu, C, DuVernois, MA, Flaherty, J, Friedman, E, Gaior, R, Gaswint, G, Glaser, C, Hallgren, A, Hallmann, S, Ham, Y-B, Hanson, JC, Harty, N, Hendricks, B, Hoffman, KD, Hong, E, Hornhuber, C, Hsu, SY, Hu, L, Huang, JJ, Huang, M-H, Hughes, K, Ishihara, A, Jee, G, Jung, J, Karle, A, Kelley, JL, Klein, SR, Kleinfelder, SA, Kim, J, Kim, K-C, Kim, M-C, Kravchenko, I, Krebs, R, Ku, Y, Kuo, CY, Kurusu, K, Kwon, Hyuck-Jin, Lahmann, R, Landsman, H, Latif, U, Lee, C, Leung, C-H, Li, C-J, Liu, J, Liu, T-C, Lu, M-Y, Madison, K, Mammo, J, Mase, K, McAleer, S, Meures, T, Meyers, ZS, Michaels, K, Mikhailova, M, Mulrey, K, Nam, J, Nichol, RJ, Nir, G, Nelles, A, Novikov, A, Nozdrina, A, Oberla, E, Oeyen, B, Osborn, J, Pan, Y, Pandya, H, Paul, MP, Persichilli, C, Pfendner, C, Plaisier, I, and Punsuebsay, N
Subjects: Particle and High Energy Physics, Physical Sciences, Neutrino, Ultra-high energy cosmic rays, Background rejection, Triboelectric effect, Astronomical and Space Sciences, Atomic, Molecular, Nuclear, Particle and Plasma Physics, Nuclear & Particles Physics, Astronomical sciences, Particle and high energy physics
Abstract: In the hopes of observing the highest-energy neutrinos (E>1 EeV) populating the Universe, both past (RICE, AURA, ANITA) and current (RNO-G, ARIANNA, ARA and TAROGE-M) polar-sited experiments exploit the impulsive radio emission produced by neutrino interactions. In such experiments, rare single event candidates must be unambiguously identified above backgrounds. Background rejection strategies to date primarily target thermal noise fluctuations and also impulsive radio-frequency signals of anthropogenic origin. In this paper, we consider the possibility that ‘fake’ neutrino signals may also be generated naturally via the ‘triboelectric effect.’ This broadly describes any process in which force applied at a boundary layer results in displacement of surface charge, leading to the production of an electrostatic potential difference ΔV. Wind blowing over granular surfaces such as snow can induce such a potential difference, with subsequent coronal discharge. Discharges over timescales as short as nanoseconds can then lead to radio-frequency emissions at characteristic MHz–GHz frequencies. Using data from various past (RICE, AURA, SATRA, ANITA) and current (RNO-G, ARIANNA and ARA) neutrino experiments, we find evidence for such backgrounds, which are generally characterized by: (a) a threshold wind velocity which likely depends on the experimental trigger criteria and layout; for the experiments considered herein, this value is typically O(10 m/s), (b) frequency spectra generally shifted to the low-end of the frequency regime to which current radio experiments are typically sensitive (100–200 MHz), (c) for the strongest background signals, an apparent preference for discharges from above-surface structures, although the presence of more isotropic, lower amplitude triboelectric discharges cannot be excluded.
Published: 2023

4. A low-threshold ultrahigh-energy neutrino search with the Askaryan Radio Array

Author: Allison, P., Archambault, S., Beatty, J. J., Besson, D. Z., Bishop, A., Chen, C. C., Chen, C. H., Chen, P., Chen, Y. C., Clark, B. A., Clay, W., Connolly, A., Cremonesi, L., Dasgupta, P., Davies, J., de Kockere, S., de Vries, K. D., Deaconu, C., DuVernois, M. A., Flaherty, J., Friedman, E., Gaior, R., Hanson, J., Harty, N., Hendricks, B., Hoffman, K. D., Hong, E., Hsu, S. Y., Hu, L., Huang, J. J., Huang, M. -H., Hughes, K., Ishihara, A., Karle, A., Kelley, J. L., Kim, K. -C., Kim, M. -C., Kravchenko, I., Krebs, R., Ku, Y., Kuo, C. Y., Kurusu, K., Landsman, H., Latif, U. A., Li, C. -J., Liu, T. -C., Lu, M. -Y., Madison, B., Madison, K., Mase, K., Meures, T., Nam, J., Nichol, R. J., Nir, G., Novikov, A., Nozdrina, A., Oberla, E., Osborn, J., Pan, Y., Pfendner, C., Punsuebsay, N., Roth, J., Seckel, D., Seikh, M. F. H., Shiao, Y. -S., Shultz, A., Smith, D., Toscano, S., Torres, J., Touart, J., van Eijndhoven, N., Varner, G. S., Vieregg, A., Wang, M. -Z., Wang, S. -H., Wang, Y. H., Wissel, S. A., Xie, C., Yoshida, S., and Young, R.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: In the pursuit of the measurement of the still-elusive ultrahigh-energy (UHE) neutrino flux at energies of order EeV, detectors using the in-ice Askaryan radio technique have increasingly targeted lower trigger thresholds. This has led to improved trigger-level sensitivity to UHE neutrinos. Working with data collected by the Askaryan Radio Array (ARA), we search for neutrino candidates at the lowest threshold achieved to date, leading to improved analysis-level sensitivities. A neutrino search on a data set with 208.7~days of livetime from the reduced-threshold fifth ARA station is performed, achieving a 68\% analysis efficiency over all energies on a simulated mixed-composition neutrino flux with an expected background of $0.10_{-0.04}^{+0.06}$ events passing the analysis. We observe one event passing our analysis and proceed to set a neutrino flux limit using a Feldman-Cousins construction. We show that the improved trigger-level sensitivity can be carried through an analysis, motivating the Phased Array triggering technique for use in future radio-detection experiments. We also include a projection using all available data from this detector. Finally, we find that future analyses will benefit from studies of events near the surface to fully understand the background expected for a large-scale detector., Comment: 15 pages, 8 figures
Published: 2022
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5. Triboelectric Backgrounds to radio-based UHE Neutrino Exeperiments

Author: Aguilar, J. A., Anker, A., Allison, P., Archambault, S., Baldi, P., Barwick, S. W., Beatty, J. J., Beise, J., Besson, D., Bishop, A., Bondarev, E., Botner, O., Bouma, S., Buitink, S., Cataldo, M., Chen, C. C., Chen, C. H., Chen, P., Chen, Y. C., Clark, B. A., Clay, W., Curtis-Ginsberg, Z., Connolly, A., Dasgupta, P., de Kockere, S., de Vries, K. D., Deaconu, C., DuVernois, M. A., Flaherty, J., Friedman, E., Gaior, R., Gaswint, G., Glaser, C., Hallgren, A., Hallmann, S., Hanson, J. C., Harty, N., Hendricks, B., Hoffman, K. D., Hornhuber, C., Hsu, S. Y., Hu, L., Huang, J. J., Huang, M. -H., Hughes, K., Ishihara, A., Karle, A., Kelley, J. L., Klein, S. R., Kleinfelder, S. A., Kim, K. -C., Kim, M. -C., Kravchenko, I., Krebs, R., Ku, Y., Kuo, C. Y., Kurusu, K., Lahmann, R., Landsman, H., Latif, U., Li, C. -J., Liu, J., Liu, T. -C., Lu, M. -Y., Madison, K., Mammo, J., Mase, K., McAleer, S., Meures, T., Meyers, Z. S., Michaels, K., Mikhailova, M., Mulrey, K., Nam, J., Nichol, R. J., Nelles, A., Novikov, A., Nozdrina, A., Oberla, E., Oeyen, B., Osborn, J., Pan, Y., Pandya, H., Paul, M. P., Persichilli, C., Plaisier, I., Punsuebsay, N., Pyras, L., Rice-Smith, R., Roth, J., Ryckbosch, D., Scholten, O., Seckel, D., Seikh, M. F. H., Shiao, Y. -S., Smith, D., Southall, D., Tatar, J., Torres, J., Toscano, S., Tosi, D., Touart, J., Broeck, D. J. Van Den, van Eijndhoven, N., Varner, G. S., Vieregg, A. G., Wang, M. -Z., Wang, S. -H, Wang, Y. H., Welling, C., Williams, D. R., Wissel, S., Xie, C., Yoshida, S., Young, R., Zhao, L., and Zink, A.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Abstract: The proposed IceCube-Gen2 (ICG2) seeks to instrument ~500 sq. km of Antarctic ice near the geographic South Pole with radio antennas, in order to observe the highest energy (E>1 EeV) neutrinos in the Universe. To this end, ICG2 will use the impulsive radio-frequency (RF) signal produced by neutrino interactions in polar ice caps. In such experiments, rare single event candidates must be unambiguously separated from background; to date, signal identification strategies primarily reject thermal noise and anthropogenic backgrounds. Here, we consider the possibility that fake neutrino signals may also be naturally generated via the 'triboelectric effect'. This broadly includes any process in which force applied at a boundary layer results in displacement of surface charge, generating a potential difference {\Delta}V. Wind blowing over granular surfaces such as snow can induce such a {\Delta}V, with subsequent discharge. Discharges over nanosecond-timescales can then lead to RF emissions at characteristic MHz-GHz frequencies. We find that such backgrounds are evident in the several neutrino experiments considered, and are generally characterized by: a) a threshold wind velocity which likely depends on the experimental signal trigger threshold and layout; for the experiments considered herein, this value is typically O(10 m/s), b) frequency spectra generally shifted to the low-end of the frequency regime to which current radio experiments are typically sensitive (100-200 MHz), c) for the strongest background signals, an apparent preference for discharges from above-surface structures, although the presence of more isotropic, lower amplitude triboelectric discharges cannot be excluded.
Published: 2021

6. Constraints on the Diffuse Flux of Ultra-High Energy Neutrinos from Four Years of Askaryan Radio Array Data in Two Stations

Author: ARA Collaboration, Allison, P., Archambault, S., Beatty, J. J., Beheler-Amass, M., Besson, D. Z., Beydler, M., Chen, C. C., Chen, C. H., Chen, P., Clark, B. A., Clay, W., Connolly, A., Cremonesi, L., Davies, J., de Kockere, S., de Vries, K. D., Deaconu, C., Duvernois, M., Friedman, E., Gaior, R., Hanson, J., Hanson, K., Hoffman, K. D., Hokanson-Fasig, B., Hong, E., Hsu, S. Y., Hu, L., Huang, J. J., Huang, M. -H., Hughes, K., Ishihara, A., Karle, A., Kelley, J. L., Khandelwal, R., Kim, K. -C., Kim, M. -C., Kravchenko, I., Kurusu, K., Landsman, H., Latif, U. A., Laundrie, A., Li, C. -J., Liu, T. -C., Lu, M. -Y., Madison, B., Mase, K., Meures, T., Nam, J., Nichol, R. J., Nir, G., Novikov, A., Nozdrina, A., Oberla, E., O'Murchadha, A., Osborn, J., Pan, Y., Pfendner, C., Roth, J., Sandstrom, P., Seckel, D., Shiao, Y. -S., Shultz, A., Smith, D., Torres, J., Touart, J., van Eijndhoven, N., Varner, G. S., Vieregg, A. G., Wang, M. -Z., Wang, S. -H., Wissel, S. A., Yoshida, S., and Young, R.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: The Askaryan Radio Array (ARA) is an ultra-high energy (UHE, $>10^{17}$ eV) neutrino detector designed to observe neutrinos by searching for the radio waves emitted by the relativistic products of neutrino-nucleon interactions in Antarctic ice. In this paper, we present constraints on the diffuse flux of ultra-high energy neutrinos between $10^{16}-10^{21}$ eV resulting from a search for neutrinos in two complementary analyses, both analyzing four years of data (2013-2016) from the two deep stations (A2, A3) operating at that time. We place a 90 % CL upper limit on the diffuse all flavor neutrino flux at $10^{18}$ eV of $EF(E)=5.6\times10^{-16}$ $\textrm{cm}^{-2}$$\textrm{s}^{-1}$$\textrm{sr}^{-1}$. This analysis includes four times the exposure of the previous ARA result, and represents approximately 1/5 the exposure expected from operating ARA until the end of 2022., Comment: 12 pages, 7 figures; Accepted to PRD
Published: 2019
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7. Long-baseline horizontal radio-frequency transmission through polar ice

Author: Allison, P., Archambault, S., Beatty, J. J., Besson, D. Z., Chen, C. C., Chen, C. H., Chen, P., Christenson, A., Clark, B. A., Clay, W., Connolly, A., Cremonesi, L., Deaconu, C., Duvernois, M., Friedman, L., Gaior, R., Hanson, J., Hanson, K., Haugen, J., Hoffman, K. D., Hong, E., Hsu, S. Y., Hu, L., Huang, J. J., Huang, A. M. -H., Hughes, K., Ishihara, A., Karle, A., Kelley, J. L., Khandelwal, R., Kim, M. -C., Kravchenko, I., Kruse, J., Kurusu, K., Kuwabara, T., Latif, U. A., Laundrie, A., Li, C. -J., Liu, T. -C., Lu, M. -Y., Madison, B., Mase, K., Meures, T., Nam, J., Nichols, R. J., Novikov, A., Nozdrina, A., Oberla, E., Pan, Y., Pfendner, C., Relich, M., Sandstrom, P., Seckel, D., Shiao, Y. S., Shultz, A., Smith, D., Song, M., Torres, J., Touart, J., Varner, G. S., Vieregg, A., Wang, M. Z., Wang, S. H., Wissel, S., Yoshida, S., and Young, R.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: We report on analysis of englacial radio-frequency (RF) pulser data received over horizontal baselines of 1--5 km, based on broadcasts from two sets of transmitters deployed to depths of up to 1500 meters at the South Pole. First, we analyze data collected usingtwo RF bicone transmitters 1400 meters below the ice surface, and frozen into boreholes drilled for the IceCube experiment in 2011. Additionally, in Dec., 2018, a fat-dipole antenna, fed by one of three high-voltage (~1 kV), fast (~(1-5 ns)) signal generators was lowered into the 1700-m deep icehole drilled for the South Pole Ice Core Experiment (SPICE), approximately 3 km from the geographic South Pole. Signals from transmitters were recorded on the five englacial multi-receiver ARA stations, with receiver depths between 60--200 m. We confirm the long, >1 km RF electric field attenuation length, test our observed signal arrival timing distributions against models, and measure birefringent asymmetries at the 0.15% level.
Published: 2019
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8. The Next-Generation Radio Neutrino Observatory -- Multi-Messenger Neutrino Astrophysics at Extreme Energies

Author: Aguilar, J. A., Allison, P., Archambault, S., Beatty, J. J., Besson, D. Z., Botner, O., Buitink, S., Chen, P., Clark, B. A., Connolly, A., Deaconu, C., de Kockere, S., DuVernois, M. A., van Eijndhoven, N., Finley, C., Garcia, D., Hallgren, A., Halzen, F., Hanson, J., Hanson, K., Heros, C. Pérez de los, Hoffman, K. D., Hokanson-Fasig, B., Hughes, K., Hultqvist, K., Ishihara, A., Karle, A., Kelley, J. L., Klein, S. R., Kowalski, M., Kravchenko, I., Latif, U. A., Liu, T. C., Lu, M. -Y., Mase, K., Morse, R., Nam, J., Nelles, A., Oberla, E., Pfendner, C., Pan, Y., Plaisier, I., Prohira, S., Robertson, S., Rolla, J., Ryckbosch, D., Schröder, F. G., Seckel, D., Shultz, A., Smith, D., Southall, D., O'Sullivan, E., Toscano, S., Torres-Espinosa, J., Unger, E., Vieregg, A. G., de Vries, K., Wang, S. -H., Welling, C., Wissel, S. A., and Yoshida, S.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: RNO is the mid-scale discovery instrument designed to make the first observation of neutrinos from the cosmos at extreme energies, with sensitivity well beyond current instrument capabilities. This new observatory will be the largest ground-based neutrino telescope to date, enabling the measurement of neutrinos above $10^{16}$ eV, determining the nature of the astrophysical neutrino flux that has been measured by IceCube at higher energies, similarly extending the reach of multi-messenger astrophysics to the highest energies, and enabling investigations of fundamental physics at energies unreachable by particle accelerators on Earth., Comment: 14 pages including references, 5 figures, submitted to the Decadal Survey on Astronomy and Astrophysics (Astro2020)
Published: 2019

9. Recent Results from The Askaryan Radio Array

Author: ARA Collaboration, Allison, P., Archambault, S., Bard, R., Beatty, J. J., Beheler-Amass, M., Besson, D. Z., Beydler, M., Chen, C. -C., Chen, C. -H., Chen, P., Clark, B., Clough, A., Connolly, A., Davies, J., Deaconu, C., DuVernois, M. A., Fender, C., Friedman, E., Hanson, J., Hanson, K., Haugen, J., Hoffman, K. D., Hong, E., Hsu, S. -Y., Hu, L., Huang, J. -J., Huang, M. -H., Ishihara, A., Karle, A., Kelley, J. L., Khandelwal, R., Kim, M., Kravchenko, I., Kruse, J., Kurusu, K., Landsman, H., Latif, U. A., Laundrie, A., Li, C. -J., Liu, T. C., Lu, M. -Y., Mase, K., Meures, T., Nam, J., Nichol, R. J., Nir, G., Oberla, E., O'Murchadha, A., Pan, Y., Ratzlaff, K., Roth, J., Sandstrom, P., Seckel, D., Shiao, Y. -S., Shultz, A., Song, M., Touart, J., Vieregg, A. G., Wang, M. -Z., Wang, S. -H., Wissel, S. A., Yoshida, S., and Young, R.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: The Askaryan Radio Array (ARA) is an ultra-high energy (UHE) neutrino telescope at the South Pole consisting of an array of radio antennas aimed at detecting the Askaryan radiation produced by neutrino interactions in the ice. Currently, the experiment has five stations in operation that have been deployed in stages since 2012. This contribution focuses on the development of a search for a diffuse flux of neutrinos in two ARA stations (A2 and A3) from 2013-2016. A background of $\sim 0.01-0.02$ events is expected in one station in each of two search channels in horizontal- and vertical-polarizations. The expected new constraints on the flux of ultra-high energy neutrinos based on four years of analysis with two stations improve on the previous limits set by ARA by a factor of about two. The projected sensitivity of ARA's five-station dataset is beginning to be competitive with other neutrino telescopes at high energies near $10^{10.5}\,$GeV., Comment: 7 pages, 5 figures, prepared for proceedings for the International Cosmic Ray Conference, Madison, WI, 2019
Published: 2019

10. Triboelectric backgrounds to radio-based polar ultra-high energy neutrino (UHEN) experiments

Author: Aguilar, J.A., Anker, A., Allison, P., Archambault, S., Baldi, P., Barwick, S.W., Beatty, J.J., Beise, J., Besson, D., Bishop, A., Bondarev, E., Botner, O., Bouma, S., Buitink, S., Cataldo, M., Chen, C.C., Chen, C.H., Chen, P., Chen, Y.C., Choi, T., Clark, B.A., Clay, W., Curtis-Ginsberg, Z., Connolly, A., Cremonesi, L., Dasgupta, P., Davies, J., de Kockere, S., de Vries, K.D., Deaconu, C., DuVernois, M.A., Flaherty, J., Friedman, E., Gaior, R., Gaswint, G., Glaser, C., Hallgren, A., Hallmann, S., Ham, Y.-B., Hanson, J.C., Harty, N., Hendricks, B., Hoffman, K.D., Hong, E., Hornhuber, C., Hsu, S.Y., Hu, L., Huang, J.J., Huang, M.-H., Hughes, K., Ishihara, A., Jee, G., Jung, J., Karle, A., Kelley, J.L., Klein, S.R., Kleinfelder, S.A., Kim, J., Kim, K.-C., Kim, M.-C., Kravchenko, I., Krebs, R., Ku, Y., Kuo, C.Y., Kurusu, K., Kwon, Hyuck-Jin, Lahmann, R., Landsman, H., Latif, U., Lee, C., Leung, C.-H., Li, C.-J., Liu, J., Liu, T.-C., Lu, M.-Y., Madison, K., Mammo, J., Mase, K., McAleer, S., Meures, T., Meyers, Z.S., Michaels, K., Mikhailova, M., Mulrey, K., Nam, J., Nichol, R.J., Nir, G., Nelles, A., Novikov, A., Nozdrina, A., Oberla, E., Oeyen, B., Osborn, J., Pan, Y., Pandya, H., Paul, M.P., Persichilli, C., Pfendner, C., Plaisier, I., Punsuebsay, N., Pyras, L., Rice-Smith, R., Roth, J., Ryckbosch, D., Scholten, O., Seckel, D., Seikh, M.F.H., Shiao, Y.-S., Shin, B.-K., Shultz, A., Smith, D., Southall, D., Tatar, J., Torres, J., Toscano, S., Tosi, D., Touart, J., Van Den Broeck, D.J., van Eijndhoven, N., Varner, G.S., Vieregg, A.G., Wang, M.-Z., Wang, S.-H., Wang, Y.H., Welling, C., Williams, D.R., Wissel, S., Xie, C., Yoshida, S., Young, R., Zhao, L., and Zink, A.
Published: 2023
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11. Design and Performance of an Interferometric Trigger Array for Radio Detection of High-Energy Neutrinos

Author: Allison, P., Archambault, S., Bard, R., Beatty, J. J., Beheler-Amass, M., Besson, D. Z., Beydler, M., Bogdan, M., Chen, C. -C., Chen, C. -H., Chen, P., Clark, B. A., Clough, A., Connolly, A., Cremonesi, L., Davies, J., Deaconu, C., DuVernois, M. A., Friedman, E., Hanson, J., Hanson, K., Haugen, J., Hoffman, K. D., Hokanson-Fasig, B., Hong, E., Hsu, S. -Y., Hu, L., Huang, J. -J., Huang, M. -H., Hughes, K., Ishihara, A., Karle, A., Kelley, J. L., Khandelwal, R., Kim, M., Kravchenko, I., Kruse, J., Kurusu, K., Landsman, H., Latif, U. A., Laundrie, A., Li, C. -J., Liu, T. C., Lu, M. -Y., Ludwig, A., Mase, K., Meures, T., Nam, J., Nichol, R. J., Nir, G., Oberla, E., OMurchadha, A., Pan, Y., Pfendner, C., Ransom, M., Ratzla, K., Roth, J., Sandstrom, P., Seckel, D., Shiao, Y. -S., Shultz, A., Smith, D., Song, M., Sullivan, M., Touart, J., Vieregg, A. G., Wang, M. -Z., Wang, S. -H., Wei, K., Wissel, S. A., Yoshida, S., and Young, R.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics, Physics - Instrumentation and Detectors
Abstract: Ultra-high energy neutrinos are detectable through impulsive radio signals generated through interactions in dense media, such as ice. Subsurface in-ice radio arrays are a promising way to advance the observation and measurement of astrophysical high-energy neutrinos with energies above those discovered by the IceCube detector ($\geq$1 PeV) as well as cosmogenic neutrinos created in the GZK process ($\geq$100 PeV). Here we describe the $\textit{NuPhase}$ detector, which is a compact receiving array of low-gain antennas deployed 185 m deep in glacial ice near the South Pole. Signals from the antennas are digitized and coherently summed into multiple beams to form a low-threshold interferometric phased array trigger for radio impulses. The NuPhase detector was installed at an Askaryan Radio Array (ARA) station during the 2017/18 Austral summer season. $\textit{In situ}$ measurements with an impulsive, point-source calibration instrument show a 50% trigger efficiency on impulses with voltage signal-to-noise ratios (SNR) of $\le$2.0, a factor of $\sim$1.8 improvement in SNR over the standard ARA combinatoric trigger. Hardware-level simulations, validated with $\textit{in situ}$ measurements, predict a trigger threshold of an SNR as low as 1.6 for neutrino interactions that are in the far field of the array. With the already-achieved NuPhase trigger performance included in ARASim, a detector simulation for the ARA experiment, we find the trigger-level effective detector volume is increased by a factor of 1.8 at neutrino energies between 10 and 100 PeV compared to the currently used ARA combinatoric trigger. We also discuss an achievable near term path toward lowering the trigger threshold further to an SNR of 1.0, which would increase the effective single-station volume by more than a factor of 3 in the same range of neutrino energies., Comment: 19 pages, 19 figures, submitted to Nuclear Instruments and Methods in Physics Research A
Published: 2018
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12. Observation of Reconstructable Radio Emission Coincident with an X-Class Solar Flare in the Askaryan Radio Array Prototype Station

Author: Allison, P., Archambault, S., Auffenberg, J., Bard, R., Beatty, J. J., Beheler-Amass, M., Besson, D. Z., Beydler, M., Bora, C., Chen, C. -C., Chen, C. -H., Chen, P., Clark, B. A., Clough, A., Connolly, A., Davies, J., Deaconu, C., DuVernois, M. A., Friedman, E., Fox, B., Gorham, P. W., Hanson, J., Hanson, K., Haugen, J., Hill, B., Hoffman, K. D., Hong, E., Hsu, S. -Y., Hu, L., Huang, J. -J., Huang, M. -H., Ishihara, A., Karle, A., Kelley, J. L., Khandelwal, R., Kim, M., Kravchenko, I., Kruse, J., Kurusu, K., Landsman, H., Latif, U. A., Laundrie, A., Li, C. -J., Liu, T. C., Lu, M. -Y., Mase, K., Maunu, R., Meures, T., Miki, C., Nam, J., Nichol, R. J., Nir, G., Oberla, E., ÓMurchadha, A., Pan, Y., Pfendner, C., Ratzlaff, K., Richman, M., Roth, J., Rotter, B., Sandstrom, P., Seckel, D., Shiao, Y. -S., Shultz, A., Song, M., Stockham, J., Stockham, M., Sullivan, M., Touart, J., Tu, H. -Y., Varner, G. S., Vieregg, A. G., Wang, M. -Z., Wang, S. -H., Wissel, S. A., Yoshida, S., and Young, R.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics
Abstract: The Askaryan Radio Array (ARA) reports an observation of radio emission coincident with the "Valentine's Day" solar flare on Feb. 15$^{\rm{th}}$, 2011 in the prototype "Testbed" station. We find $\sim2000$ events that passed our neutrino search criteria during the 70 minute period of the flare, all of which reconstruct to the location of the sun. A signal analysis of the events reveals them to be consistent with that of bright thermal noise correlated across antennas. This is the first natural source of radio emission reported by ARA that is tightly reconstructable on an event-by-event basis. The observation is also the first for ARA to point radio from individual events to an extraterrestrial source on the sky. We comment on how the solar flares, coupled with improved systematic uncertainties in reconstruction algorithms, could aid in a mapping of any above-ice radio emission, such as that from cosmic-ray air showers, to astronomical locations on the sky., Comment: 18 pages, 22 figures
Published: 2018

13. Measurement of the real dielectric permittivity epsilon_r of glacial ice

Author: Allison, P., Archambault, S., Auffenberg, J., Bard, R., Beatty, J. J., Beheler-Amass, M., Besson, D. Z., Beydler, M., Brabec, C., Chen, C. -C., Chen, C. -H., Chen, P., Christenson, A., Clark, B. A., Connolly, A., Cremonesi, L., Deaconu, C., Duvernois, M., Friedman, L., Gaior, R., Gorham, P. W., Hanson, J., Hanson, K., Haugen, J., Hoffman, K. D., Hong, E., Hsu, S. -Y., Hu, L., Huang, J. -J., Huang, M. -H. A., Ishihara, A., Karle, A., Kelley, J. L., Khandelwal, R., Kim, M. -C., Kravchenko, I., Kuwabara, T., Landsman, H., Laundrie, A., Li, C. -J., Liu, T. C., Lu, M. -Y., Mase, K., Meures, T., Nam, J., Nichols, R. J., Nir, G., Novikov, A., Oberla, E., O'Murchadha, A., Pan, Y., Pfendner, C., Ratzlaff, K., Relich, M., Roth, J., Sandstrom, P., Seckel, D., Shiao, Y. -S., Shultz, A., Song, M., Touart, J., Varner, G. S., Vieregg, A., Wang, M. -Z., Wang, S. -H., Wissel, S., Yang, Y., Yoshida, S., and Young, R.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: Using data collected by the Askaryan Radio Array (ARA) experiment at the South Pole, we have used long-baseline propagation of radio-frequency signals to extract information on the radio-frequency index-of-refraction in South Polar ice. Owing to the increasing ice density over the upper 150--200 meters, rays are observed along two, nearly parallel paths, one of which is direct and a second which refracts through an inflection point, with differences in both arrival time and arrival angle that can be used to constrain the neutrino properties. We also observe indications, for the first time, of radio-frequency ice birefringence for signals propagating along predominantly horizontal trajectories, corresponding to an asymmetry of order 0.1% between the ordinary and extra-ordinary paths, numerically compatible with previous measurements of birefringent asymmetries for vertically-propagating radio-frequency signals at South Pole. Taken together, these effects offer the possibility of redundantly measuring the range from receiver to a neutrino interaction in Antarctic ice, if receiver antennas are deployed at shallow (25 m
Published: 2017

14. VERITAS contributions to the 35th International Cosmic Ray Conference

Author: Abeysekara, A. U., Archambault, S., Archer, A., Benbow, W., Bird, R., Brose, R., Buchovecky, M., Christiansen, J. L., Connolly, M. P., Cui, W., Daniel, M. K., Falcone, A., Feng, Q., Fernandez-Alonso, M., Finley, J. P., Fleischhack, H., Fortson, L., Furniss, A., Gillanders, G. H., Hütten, M., Hanna, D., Hervet, O., Holder, J., Hughes, G., Humensky, T. B., Johnson, C. A., Kaaret, P., Kar, P., Kertzman, M., Kieda, D., Krause, M., Krennrich, F., Kumar, S., Lang, M. J., Maier, G., McArthur, S., Moriarty, P., Mukherjee, R., Nieto, D., O'Brien, S., Ong, R. A., Otte, A. N., Pandel, D., Park, N., Pohl, M., Popkow, A., Pueschel, E., Quinn, J., Ragan, K., Reynolds, P. T., Roache, E., Rovero, A. C., Sadeh, I., Santander, M., Schlenstedt, S., Sembroski, G. H., Shahinyan, K., Tyler, J., Wakely, S. P., Weinstein, A., Wells, R. M., Wilcox, P., Wilhelm, A., Williams, D. A., Williamson, T. J, and Zitzer, B.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Compilation of papers presented by the VERITAS Collaboration at the 35th International Cosmic Ray Conference (ICRC), held July 12 through July 20, 2017 in Busan, South Korea., Comment: html page. 2017 ICRC, Busan, South Korea. A full list of author affiliations can be found at this link: https://veritas.sao.arizona.edu/conferences/ICRC2017_AuthList.html
Published: 2017

15. Discovery of very-high-energy emission from RGB J2243+203 and derivation of its redshift upper limit

Author: Abeysekara, A. U., Archambault, S., Archer, A., Benbow, W., Bird, R., Brose, R., Buchovecky, M., Buckley, J. H., Bugaev, V., Cerruti, M., Connolly, M. P., Cui, W., Falcone, A., Feng, Q., Finley, J. P., Fleischhack, H., Fortson, L., Furniss, A., Gillanders, G. H., Griffin, S., Grube, J., Hutten, M., Hanna, D., Hervet, O., Holder, J., Humensky, T. B., Johnson, C. A., Kaaret, P., Kar, P., Kelley-Hoskins, N., Kertzman, M., Kieda, D., Krause, M., Krennrich, F., Kumar, S., Lang, M. J., Maier, G., McArthur, S., Moriarty, P., Mukherjee, R., Nieto, D., OBrien, S., Ong, R. A., Otte, A. N., Park, N., Petrashyk, A., Poh, M., Popkow, A., Puesche, E., Quinn, J., Ragan, K., Reynolds, P. T., Richards, G. T., Roache, E., Rulten, C., Sadeh, I., Santander, M., Sembroski, G. H., Shahinyan, K., Staszak, D., Telezhinsky, I., Tyler, J., Vassiliev, V. V., Wakely, S. P., Weiner, O. M., Weinstein, A., Wilcox, P., Wilhelm, A., Williams, D. A., and Zitzer, B.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
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 $<~0.9$ to z $<~1.1$.
Published: 2017
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16. Very-High-Energy $\gamma$-Ray Observations of the Blazar 1ES 2344+514 with VERITAS

Author: Allen, C., Archambault, S., Archer, A., Benbow, W., Bird, R., Bourbeau, E., Brose, R., Buchovecky, M., Buckley, J. H., Bugaev, V., Cardenzana, J. V, Cerruti, M., Chen, X., Christiansen, J. L., Connolly, M. P., Cui, W., Daniel, M. K., Eisch, J. D., Falcone, A., Feng, Q., Fernandez-Alonso, M., Finley, J. P., Fleischhack, H., Flinders, A., Fortson, L., Furniss, A., Gillanders, G. H., Griffin, S., Grube, J., Hütten, M., Håkansson, N., Hanna, D., Hervet, O., Holder, J., Hughes, G., Humensky, T. B., Johnson, C. A., Kaaret, P., Kar, P., Kelley-Hoskins, N., Kertzman, M., Kieda, D., Krause, M., Krennrich, F., Kumar, S., Lang, M. J., Maier, G., McArthur, S., McCann, A., Meagher, K., Moriarty, P., Mukherjee, R., Nguyen, T., Nieto, D., O'Brien, S., de Bhróithe, A. O'Faoláin, Ong, R. A., Otte, A. N., Park, N., Petrashyk, A., 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., Wilhelm, A., and Williams, D. A.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
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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17. Dark Matter Constraints from a Joint Analysis of Dwarf Spheroidal Galaxy Observations with VERITAS

Author: VERITAS Collaboration, Archambault, S., Archer, A., Benbow, W., Bird, R., Bourbeau, E., Brantseg, T., Buchovecky, M., Buckley, J. H., Bugaev, V., Byrum, K., Cerruti, M., Christiansen, J. L., Connolly, M. P., Cui, W., Daniel, M. K., Feng, Q., Finley, J. P., Fleischhack, H., Fortson, L., Furniss, A., Geringer-Sameth, A., Griffin, S., Grube, J., Hütten, M., Håkansson, N., Hanna, D., Hervet, O., Holder, J., Hughes, G., Johnson, C. A., Kaaret, P., Kar, P., Kelley-Hoskins, N., Kertzman, M., Kieda, D., Koushiappas, S., Krause, M., Kumar, S., Lang, M. J., Lin, T. T. Y., McArthur, S., Moriarty, P., Nieto, D., O'Brien, S., Ong, R. A., Otte, A. N., Park, N., Pohl, M., Popkow, A., Pueschel, E., Quinn, J., Ragan, K., Reynolds, P. T., Richards, G. T., Roache, E., Rulten, C., Sadeh, I., Santander, M., Sembroski, G. H., Shahinyan, K., Smith, A. W., Staszak, D., Telezhinsky, I., Trépanier, S., Tucci, J. V., Tyler, J., Wakely, S. P., Weinstein, A., Wilcox, P., Williams, D. A., and Zitzer, B.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We present constraints on the annihilation cross section of WIMP dark matter based on the joint statistical analysis of four dwarf galaxies with VERITAS. These results are derived from an optimized photon weighting statistical technique that improves on standard imaging atmospheric Cherenkov telescope (IACT) analyses by utilizing the spectral and spatial properties of individual photon events. We report on the results of $\sim$230 hours of observations of five dwarf galaxies and the joint statistical analysis of four of the dwarf galaxies. We find no evidence of gamma-ray emission from any individual dwarf nor in the joint analysis. The derived upper limit on the dark matter annihilation cross section from the joint analysis is $1.35\times 10^{-23} {\mathrm{ cm^3s^{-1}}}$ at 1 TeV for the bottom quark ($b\bar{b}$) final state, $2.85\times 10^{-24}{\mathrm{ cm^3s^{-1}}}$ at 1 TeV for the tau lepton ($\tau^{+}\tau^{-}$) final state and $1.32\times 10^{-25}{\mathrm{ cm^3s^{-1}}}$ at 1 TeV for the gauge boson ($\gamma\gamma$) final state., Comment: 14 pages, 9 figures, published in PRD, Ascii tables containing annihilation cross sections limits are available for download as ancillary files with readme.txt file description of limits
Published: 2017
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18. Gamma-ray Observations Under Bright Moonlight with VERITAS

Author: Archambault, S., Archer, A., Benbow, W., Bird, R., Bourbeau, E., Bouvier, A., Buchovecky, M., Bugaev, V., Cardenzana, J. V, Cerruti, M., Ciupik, L., Connolly, M. P., Cui, W., Daniel, M. K., Errando, M., Falcone, A., Feng, Q., Finley, J. P., Fleischhack, H., Fortson, L., Furniss, A., Gillanders, G. H., Griffin, S., Hanna, D., Hervet, O., Holder, J., Hughes, G., Humensky, T. B., Hütten, M., Johnson, C. A., Kaaret, P., Kar, P., Kertzman, M., Kieda, D., Krause, M., Lang, M. J., Maier, G., McArthur, S., Moriarty, P., Mukherjee, R., Nieto, D., O'Brien, S., Ong, R. A., Otte, A. N., Park, N., Pohl, M., Popkow, A., Pueschel, E., Quinn, J., Ragan, K., Reynolds, P. T., Richards, G. T., Roache, E., Rulten, C., Sadeh, I., Sembroski, G. H., Shahinyan, K., Staszak, D., Telezhinsky, I., Trepanier, S., Wakely, S. P., Weinstein, A., Wilcox, P., Williams, D. A., and Zitzer, B.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: 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: 2017
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19. Gamma-ray observations of Tycho's SNR with VERITAS and Fermi

Author: VERITAS Collaboration, Archambault, S., Archer, A., Benbow, W., Bird, R., Bourbeau, E., Buchovecky, M., Buckley, J. H., Bugaev, V., Cerruti, M., Connolly, M. P., Cui, W., Dwarkadas, V. V., Errando, M., Falcone, A., Feng, Q., Finley, J. P., Fleischhack, H., Fortson, L., Furniss, A., Griffin, S., Hutten, M., Hanna, D., Holder, J., Johnson, C. A., Kaaret, P., Kar, P., Kelley-Hoskins, N., Kertzman, M., Kieda, D., Krause, M., Kumar, S., Lang, M. J., Maier, G., McArthur, S., McCann, A., Moriarty, P., Mukherjee, R., Nieto, D., O'Brien, S., Ong, R. A., Otte, A. N., Park, N., Pohl, M., Popkow, A., Pueschel, E., Quinn, J., Ragan, K., Reynolds, P. T., Richards, G. T., Roache, E., Sadeh, I., Santander, M., Sembroski, G. H., Shahinyan, K., Slane, P., Staszak, D., Telezhinsky, I., Trepanier, S., Tyler, J., Wakely, S. P., Weinstein, A., Weisgarber, T., Wilcox, P., Wilhelm, A., Williams, D. A., and Zitzer, B.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: High-energy gamma-ray emission from supernova remnants (SNRs) has provided a unique perspective for studies of Galactic cosmic-ray acceleration. Tycho's SNR is a particularly good target because it is a young, type Ia SNR that is well-studied over a wide range of energies and located in a relatively clean environment. Since the detection of gamma-ray emission from Tycho's SNR by VERITAS and Fermi-LAT, there have been several theoretical models proposed to explain its broadband emission and high-energy morphology. We report on an update to the gamma-ray measurements of Tycho's SNR with 147 hours of VERITAS and 84 months of Fermi-LAT observations, which represents about a factor of two increase in exposure over previously published data. About half of the VERITAS data benefited from a camera upgrade, which has made it possible to extend the TeV measurements toward lower energies. The TeV spectral index measured by VERITAS is consistent with previous results, but the expanded energy range softens a straight power-law fit. At energies higher than 400 GeV, the power-law index is $2.92 \pm 0.42_{\mathrm{stat}} \pm 0.20_{\mathrm{sys}}$. It is also softer than the spectral index in the GeV energy range, $2.14 \pm 0.09_{\mathrm{stat}} \pm 0.02_{\mathrm{sys}}$, measured by this study using Fermi--LAT data. The centroid position of the gamma-ray emission is coincident with the center of the remnant, as well as with the centroid measurement of Fermi--LAT above 1 GeV. The results are consistent with an SNR shell origin of the emission, as many models assume. The updated spectrum points to a lower maximum particle energy than has been suggested previously., Comment: Accepted for publication in The Astrophysical Journal
Published: 2017
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20. A luminous and isolated gamma-ray flare from the blazar B2 1215+30

Author: VERITAS Collaboration, Abeysekara, A. U., Archambault, S., Archer, A., Benbow, W., Bird, R., Buchovecky, M., Buckley, J. H., Bugaev, V., Byrum, K., Cerruti, M., Chen, X., Ciupik, L., Cui, W., Dickinson, H. J., Eisch, J. D., Errando, M., Falcone, A., Feng, Q., Finley, J. P., Fleischhack, H., Fortson, L., Furniss, A., Gillanders, G. H., Griffin, S., Grube, J., Hutten, M., Hakansson, N., Hanna, D., Holder, J., Humensky, T. B., Johnson, C. A., Kaaret, P., Kar, P., Kertzman, M., Kieda, D., Krause, M., Krennrich, F., Kumar, S., Lang, M. J., Maier, G., McArthur, S., McCann, A., Meagher, K., Moriarty, P., Mukherjee, R., Nguyen, T., Nieto, D., Ong, R. A., Otte, A. N., Park, N., Pelassa, V., Pohl, M., Popkow, A., Pueschel, E., Quinn, J., Ragan, K., Reynolds, P. T., Richards, G. T., Roache, E., Rulten, C., Santander, M., Sembroski, G. H., Shahinyan, K., Staszak, D., Telezhinsky, I., Tucci, J. V., Tyler, J., Wakely, S. P., Weiner, O. M., Weinstein, A., Wilhelm, A., Williams, D. A., Collaboration, Fermi-LAT, Fegan, S., Giebels, B., Horan, D., Berdyugin, A., Kuan, J., Lindfors, E., Nilsson, K., Oksanen, A., Prokoph, H., Reinthal, R., Takalo, L., and Zefi, F.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: B2 1215+30 is a BL Lac-type blazar that was first detected at TeV energies by the MAGIC atmospheric Cherenkov telescopes, and subsequently confirmed by the VERITAS observatory with data collected between 2009 and 2012. In 2014 February 08, VERITAS detected a large-amplitude flare from B2 1215+30 during routine monitoring observations of the blazar 1ES 1218+304, located in the same field of view. The TeV flux reached 2.4 times the Crab Nebula flux with a variability timescale of < 3.6 h. Multiwavelength observations with Fermi-LAT, Swift, and the Tuorla observatory revealed a correlated high GeV flux state and no significant optical counterpart to the flare, with a spectral energy distribution where the gamma-ray luminosity exceeds the synchrotron luminosity. When interpreted in the framework of a one-zone leptonic model, the observed emission implies a high degree of beaming, with Doppler factor > 10, and an electron population with spectral index < 2.3., Comment: 8 pages, 3 figures, accepted for publication in The Astrophysical Journal
Published: 2017
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21. Search for Magnetically Broadened Cascade Emission From Blazars with VERITAS

Author: VERITAS Collaboration, Archambault, S., Archer, A., Benbow, W., Buchovecky, M., Bugaev, V., Cerruti, M., Connolly, M. P., Cui, W., Falcone, A., Alonso, M. Fernández, Finley, J. P., Fleischhack, H., Fortson, L., Furniss, A., Griffin, S., Hütten, M., Hervet, O., Holder, J., Humensky, T. B., Johnson, C. A., Kaaret, P., Kar, P., Kieda, D., Krause, M., Krennrich, F., Lang, M. J., Lin, T. T. Y., Maier, G., McArthur, S., Moriarty, P., Nieto, D., O'Brien, S., Ong, R. A., Otte, A. N., Pohl, M., Popkow, A., Pueschel, E., Quinn, J., Ragan, K., Reynolds, P. T., Richards, G. T., Roache, E., Rovero, A. C., Sadeh, I., Shahinyan, K., Staszak, D., Telezhinsky, I., Tyler, J., Wakely, S. P., Weinstein, A., Weisgarber, T., Wilcox, P., Wilhelm, A., Williams, D. A., and Zitzer, B.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We present a search for magnetically broadened gamma-ray emission around active galactic nuclei (AGN), using VERITAS observations of seven hard-spectrum blazars. A cascade process occurs when multi-TeV gamma rays from AGN interact with extragalactic background light (EBL) photons to produce electron-positron pairs, which then interact with cosmic microwave background (CMB) photons via inverse-Compton scattering to produce gamma rays. Due to the deflection of the electron-positron pairs, a non-zero intergalactic magnetic field (IGMF) would potentially produce detectable effects on the angular distribution of the cascade emission. In particular, an angular broadening compared to the unscattered emission could occur. Through non-detection of angularly broadened emission from 1ES 1218+304, the source with the largest predicted cascade fraction, we exclude a range of IGMF strengths around $10^{-14}$G at the 95% confidence level. The extent of the exclusion range varies with the assumptions made about the intrinsic spectrum of 1ES 1218+304 and the EBL model used in the simulation of the cascade process. All of the sources are used to set limits on the flux due to extended emission., Comment: Accepted for publication in The Astrophysical Journal
Published: 2017
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22. Multiband variability studies and novel broadband SED modeling of Mrk 501 in 2009

Author: Ahnen, M. L., Ansoldi, S., Antonelli, L. A., Antoranz, P., Babic, A., Banerjee, B., Bangale, P., de Almeida, U. Barres, Barrio, J. A., González, J. Becerra, Bednarek, W., Bernardini, E., Berti, A., 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., Wilhelmi, E. de Ona, Di Pierro, F., Doert, M., Domínguez, A., Prester, D. Dominis, Dorner, D., Doro, M., Einecke, S., Glawion, D. Eisenacher, Elsaesser, D., Engelkemeier, M., Ramazani, V. Fallah, Fernández-Barral, A., Fidalgo, D., Fonseca, M. V., Font, L., Frantzen, K., Fruck, C., Galindo, D., López, R. J. García, Garczarczyk, M., Terrats, D. Garrido, Gaug, M., Giammaria, P., Godinović, N., Munoz, A. González, 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, F., López, M., López-Coto, R., Majumdar, P., Makariev, M., Mallot, K., Maneva, G., Manganaro, M., Mannheim, K., Maraschi, L., Marcote, B., Mariotti, M., Martínez, M., Mazin, D., Menzel, U., Miranda, J. M., Mirzoyan, R., Moralejo, A., Moretti, E., Nakajima, D., Neustroev, V., Niedzwiecki, A., Rosillo, M. Nievas, Nilsson, K., Nishijima, K., Noda, K., Nogués, L., Overkemping, A., Paiano, S., Palacio, J., Palatiello, M., Paneque, D., Paoletti, R., Paredes, J. M., Paredes-Fortuny, X., Pedaletti, G., Peresano, M., Perri, L., Persic, M., Poutanen, J., Moroni, P. G. Prada, Prandini, E., Puljak, I., Reichardt, I., Rhode, W., Ribó, M., Rico, J., Garcia, J. Rodriguez, Saito, T., Satalecka, K., Schröder, S., Schultz, C., Schweizer, T., Shore, S. N., Sillanpää, A., Sitarek, J., Snidaric, I., Sobczynska, D., Stamerra, A., Steinbring, T., Strzys, M., Surić, T., Takalo, L., Tavecchio, F., Temnikov, P., Terzić, 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., Hütten, 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 III, 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, Alma, Pagani, C., Perri, M., Capalbi, M., Cesarini, A., Krimm, H. A., Kovalev, Y. Y., Kovalev, Yu. A., Ros, E., Pushkarev, A. B., Lister, M. L., Sokolovsky, K. V., Kadler, M., Piner, G., Lähteenmäki, 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: Astrophysics - High Energy Astrophysical Phenomena
Abstract: 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, Fermi-LAT, RXTE, Swift, GASP-WEBT and VLBA. We find an increase in the fractional variability with energy, while no significant interband correlations of flux changes are found in the acquired data set. The higher variability in the very high energy (>100 GeV, VHE) gamma-ray emission and the lack of correlation with the X-ray emission indicate that the highest-energy electrons that are responsible for the VHE gamma-rays do not make a dominant contribution to the ~1 keV emission. Alternatively, there could be a very variable component contributing to the VHE gamma-ray emission in addition to that coming from the synchrotron self-Compton (SSC) scenarios. 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. We find that there is some degeneracy in both the one-zone and the two-zone SSC scenarios that were probed, with several combinations of model parameters yielding a similar model-to-data agreement, and some parameters better constrained than others. The SSC model grid-scan shows that the flaring activity around 2009 May 22 cannot be modeled adequately with a one-zone SSC scenario, while it can be suitably described within a two-independent-zone SSC scenario. The observation of an electric vector polarization angle rotation coincident with the gamma-ray flare from 2009 May 1 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., Comment: 33 pages, 15 figures, accepted for publication in A&A. Corresponding authors: Marlene Doert (marlene.doert@tu-dortmund.de) and David Paneque (dpaneque@mppmu.mpg.de)
Published: 2016
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23. A search for spectral hysteresis and energy-dependent time lags from X-ray and TeV gamma-ray observations of Mrk 421

Author: Abeysekara, A. U., Archambault, S., Archer, A., Benbow, W., Bird, R., Buchovecky, M., Buckley, J. H., Bugaev, V., Cardenzana, J. V, Cerruti, M., Chen, X., Ciupik, L., Connolly, M. P., Cui, W., Eisch, J. D., Falcone, A., Feng, Q., Finley, J. P., Fleischhack, H., Flinders, A., Fortson, L., Furniss, A., Griffin, S., Hütten, M., Håkansson, N., Hanna, D., Hervet, O., Holder, J., Humensky, T. B., Kaaret, P., Kar, P., Kertzman, M., Kieda, D., Krause, M., Kumar, S., Lang, M. J., Maier, G., McArthur, S., McCann, A., Meagher, K., Moriarty, P., Mukherjee, R., Nieto, D., O'Brien, S., Ong, R. A., Otte, A. N., Park, N., Pelassa, V., Pohl, M., Popkow, A., Pueschel, E., Ragan, K., Reynolds, P. T., Richards, G. T., Roache, E., Sadeh, I., Santander, M., Sembroski, G. H., Shahinyan, K., Staszak, D., Telezhinsky, I., Tucci, J. V., Tyler, J., Wakely, S. P., Weinstein, A., Wilhelm, A., Williams, D. A., Ahnen, M. L., Ansoldi, S., Antonelli, L. A., Antoranz, P., Arcaro, C., Babic, A., Banerjee, B., Bangale, P., de Almeida, U. Barres, Barrio, J. A., González, J. Becerra, Bednarek, W., Bernardini, E., Berti, A., Biasuzzi, B., Biland, A., Blanch, O., Bonnefoy, S., Bonnoli, G., Borracci, F., Bretz, T., Carosi, R., Carosi, A., Chatterjee, A., Colin, P., Colombo, E., Contreras, J. L., Cortina, J., Covino, S., Cumani, P., Da Vela, P., Dazzi, F., De Angelis, A., De Lotto, B., Wilhelmi, E. de Oña, Di Pierro, F., Doert, M., Domínguez, A., Prester, D. Dominis, Dorner, D., Doro, M., Einecke, S., Glawion, D. Eisenacher, Elsaesser, D., Engelkemeier, M., Ramazani, V. Fallah, Fernández-Barral, A., Fidalgo, D., Fonseca, M. V., Font, L., Fruck, C., Galindo, D., López, R. J. García, Garczarczyk, M., Gaug, M., Giammaria, P., Godinović, N., Gora, D., Guberman, D., Hadasch, D., Hahn, A., Hassan, T., Hayashida, M., Herrera, J., Hose, J., Hrupec, D., Hughes, G., Idec, W., Kodani, K., Konno, Y., Kubo, H., Kushida, J., Lelas, D., Lindfors, E., Lombardi, S., Longo, F., López, M., López-Coto, R., Majumdar, P., Makariev, M., Mallot, K., Maneva, G., Manganaro, M., Mannheim, K., Maraschi, L., Marcote, B., Mariotti, M., Martínez, M., Mazin, D., Menzel, U., Mirzoyan, R., Moralejo, A., Moretti, E., Nakajima, D., Neustroev, V., Niedzwiecki, A., Rosillo, M. Nievas, Nilsson, K., Nishijima, K., Noda, K., Nogués, L., Nöthe, M., Paiano, S., Palacio, J., Palatiello, M., Paneque, D., Paoletti, R., Paredes, J. M., Paredes-Fortuny, X., Pedaletti, G., Peresano, M., Perri, L., Persic, M., Poutanen, J., Moroni, P. G. Prada, Prandini, E., Puljak, I., Garcia, J. R., Reichardt, I., Rhode, W., Ribó, M., Rico, J., Saito, T., Satalecka, K., Schroeder, S., Schweizer, T., Shore, S. N., Sillanpää, A., Sitarek, J., Snidaric, I., Sobczynska, D., Stamerra, A., Strzys, M., Surić, T., Takalo, L., Tavecchio, F., Temnikov, P., Terzić, T., Tescaro, D., Teshima, M., Torres, D. F., Torres-Albà, N., Toyama, T., Treves, A., Vanzo, G., Acosta, M. Vazquez, Vovk, I., Ward, J. E., Will, M., Wu, M. H., Zanin, R., Hovatta, T., Perez, I. de la Calle, Smith, P. S., Racero, E., and Baloković, M.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Blazars are variable emitters across all wavelengths over a wide range of timescales, from months down to minutes. It is therefore essential to observe blazars simultaneously at different wavelengths, especially in the X-ray and gamma-ray bands, where the broadband spectral energy distributions usually peak. In this work, we report on three "target-of-opportunity" (ToO) observations of Mrk 421, one of the brightest TeV blazars, triggered by a strong flaring event at TeV energies in 2014. These observations feature long, continuous, and simultaneous exposures with XMM-Newton (covering X-ray and optical/ultraviolet bands) and VERITAS (covering TeV gamma-ray band), along with contemporaneous observations from other gamma-ray facilities (MAGIC and Fermi-LAT) and a number of radio and optical facilities. Although neither rapid flares nor significant X-ray/TeV correlation are detected, these observations reveal subtle changes in the X-ray spectrum of the source over the course of a few days. We search the simultaneous X-ray and TeV data for spectral hysteresis patterns and time delays, which could provide insight into the emission mechanisms and the source properties (e.g. the radius of the emitting region, the strength of the magnetic field, and related timescales). The observed broadband spectra are consistent with a one-zone synchrotron self-Compton model. We find that the power spectral density distribution at $\gtrsim 4\times 10^{-4}$ Hz from the X-ray data can be described by a power-law model with an index value between 1.2 and 1.8, and do not find evidence for a steepening of the power spectral index (often associated with a characteristic length scale) compared to the previously reported values at lower frequencies., Comment: 45 pages, 15 figures
Published: 2016
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24. Very High-Energy Gamma-Ray Follow-Up Program Using Neutrino Triggers from IceCube

Author: IceCube Collaboration, Aartsen, M. G., Abraham, K., Ackermann, M., Adams, J., Aguilar, J. A., Ahlers, M., Ahrens, M., Altmann, D., Andeen, K., Anderson, T., Ansseau, I., Anton, G., Archinger, M., Arguelles, C., Auffenberg, J., Axani, S., Bai, X., Barwick, S. W., Baum, V., Bay, R., Beatty, J. J., Becker-Tjus, J., Becker, K. -H., BenZvi, S., Berley, D., Bernardini, E., Bernhard, A., Besson, D. Z., Binder, G., Bindig, D., Bissok, M., Blaufuss, E., Blot, S., Bohm, C., Borner, M., Bos, F., Bose, D., Boser, S., Botner, O., Braun, J., Brayeur, L., Bretz, H. -P., Bron, S., Burgman, A., Carver, T., Casier, M., Cheung, E., Chirkin, D., Christov, A., Clark, K., Classen, L., Coenders, S., Collin, G. H., Conrad, J. M., Cross, D. F. Cowen R., Day, M., de Andre, J. P. A. M., De Clercq, C., Rosendo, E. del Pino, Dembinski, H., De Ridder, S., Desiati, P., de Vries, K. D., de Wasseige, G., de With, M., DeYoung, T., Diaz-Velez, J. C., di Lorenzo, V., Dujmovic, H., Dumm, J. P., Dunkman, M., Eberhardt, B., Ehrhardt, T., Eichmann, B., Eller, P., Euler, S., Evenson, P. A., Fahey, S., Fazely, A. R., Feintzeig, J., Felde, J., Filimonov, K., Finley, C., Flis, S., Fosig, C. -C., Franckowiak, A., Franke, R., Friedman, E., Fuchs, T., Gaisser, T. K., Gallagher, J., Gerhardt, L., Ghorbani, K., Giang, W., Gladstone, L., Glauch, T., Glusenkamp, T., Goldschmidt, A., Golup, G., Gonzalez, J. G., Grant, D., Griffith, Z., Haack, C., Ismail, A. Haj, Hallgren, A., Halzen, F., Hansen, E., Hansmann, T., Hanson, K., Hebecker, D., Heereman, D., Helbing, K., Hellauer, R., Hickford, S., Hignight, J., Hill, G. C., Hoffman, K. D., Hoffmann, R., Holzapfel, K., Hoshina, K., Huang, F., Huber, M., Hultqvist, K., In, S., Ishihara, A., Jacobi, E., Japaridze, G. S., Jeong, M., Jero, K., Jones, B. J. P., Jurkovic, M., Kappes, A., Karg, T., Karle, A., Katz, U., Kauer, M., Keivani, A., Kelley, J. L., Kheirandish, A., Kim, M., Kintscher, T., Kiryluk, J., Kittler, T., Klein, S. R., Kohnen, G., Koirala, R., Kolanoski, H., Konietz, R., Kopke, L., Kopper, C., Kopper, S., Koskinen, D. J., Kowalski, M., Krings, K., Kroll, M., Kruckl, G., Kruger, C., Kunnen, J., Kunwar, S., Kurahashi, N., Kuwabara, T., Labare, M., Lanfranchi, J. L., Larson, M. J., Lauber, F., Lennarz, D., Lesiak-Bzdak, M., Leuermann, M., Lu, L., Lunemann, J., Madsen, J., Maggi, G., Mahn, K. B. M., Mancina, S., Mandelartz, M., Maruyama, R., Mase, K., Maunu, R., McNally, F., Meagher, K., Medici, M., Meier, M., Meli, A., Menne, T., Merino, G., Meures, T., Miarecki, S., Mohrmann, L., Montaruli, T., Moulai, M., Nahnhauer, R., Naumann, U., Neer, G., Niederhausen, H., Nowicki, S. C., Nygren, D. R., Pollmann, A. Obertacke, Olivas, A., O'Murchadha, A., Palczewski, T., Pandya, H., Pankova, D. V., Peiffer, P., Penek, O., Pepper, J. A., Heros, C. Perez de los, Pieloth, D., Pinat, E., Price, P. B., Przybylski, G. T., Quinnan, M., Raab, C., Radel, L., Rameez, M., Rawlins, K., Reimann, R., Relethford, B., Relich, M., Resconi, E., Rhode, W., Richman, M., Riedel, B., Robertson, S., Rongen, M., Rott, C., Ruhe, T., Ryckbosch, D., Rysewyk, D., Sabbatini, L., Sanchez-Herrera, S. E., Sandrock, A., Sandroos, J., Sarkar, S., Satalecka, K., Schlunder, P., Schmidt, T., Schoenen, S., Schoneberg, S., Schumacher, L., Seckel, D., Seunarine, S., Soldin, D., Song, M., Spiczak, G. M., Spiering, C., Stanev, T., Stasik, A., Stettner, J., Steuer, A., Stezelberger, T., Stokstad, R. G., Stossl, A., Strom, R., Strotjohann, N. L., Sullivan, G. W., Sutherland, M., Taavola, H., Taboada, I., Tatar, J., Tenholt, F., Ter-Antonyan, S., Terliuk, A., Tevsic, G., Tilav, S., Toale, P. A., Tobin, M. N., Toscano, S., Tosi, D., Tselengidou, M., Turcati, A., Unger, E., Usner, M., Vandenbroucke, J., van Eijndhoven, N., Vanheule, S., van Rossem, M., van Santen, J., Veenkamp, J., Vehring, M., Voge, M., Vogel, E., Vraeghe, M., Walck, C., Wallace, A., Wallraff, M., Wandkowsky, N., Weaver, Ch., Weiss, M. J., Wendt, C., Westerhoff, S., Whelan, B. J., Wickmann, S., Wiebe, K., Wiebusch, C. H., Wille, L., Williams, D. R., Wills, L., Wolf, M., Wood, T. R., Woolsey, E., Woschnagg, K., Xu, D. L., Xu, X. W., Xu, Y., Yanez, J. P., Yodh, G., Yoshida, S., Collaboration, M. Zoll MAGIC, Ahnen, M. L., Ansoldi, S., Antonelli, L. A., Antoranz, P., Babic, A., Banerjee, B., Bangale, P., de Almeida, U. Barres, Barrio, J. A., Gonzalez, J. Becerra, Bednarek, W., Berti, A., 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., Wilhelmi, E. de Ona, Di Pierro, F., Doert, M., Dominguez, A., Prester, D. Dominis, Dorner, D., Doro, M., Einecke, S., Glawion, D. Eisenacher, Elsaesser, D., Engelkemeier, M., Ramazani, V. Fallah, Fernandez-Barral, A., Fidalgo, D., Fonseca, M. V., Font, L., Frantzen, K., Fruck, C., Galindo, D., Lopez, R. J. Garcia, Garczarczyk, M., Terrats, D. Garrido, Gaug, M., Giammaria, P., Godinovic, N., Munoz, A. Gonzalez, 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, F., Lopez, M., Lopez-Coto, R., Majumdar, P., Makariev, M., Mallot, K., Maneva, G., Manganaro, M., Mannheim, K., Maraschi, L., Marcote, B., Mariotti, M., Martinez, M., Mazin, D., Menzel, U., Miranda, J. M., Mirzoyan, R., Moralejo, A., Moretti, E., Nakajima, D., Neustroev, V., Niedzwiecki, A., Rosillo, M. Nievas, Nilsson, K., Nishijima, K., Noda, K., Nogues, L., Overkemping, A., Paiano, S., Palacio, J., Palatiello, M., Paneque, D., Paoletti, R., Paredes, J. M., Paredes-Fortuny, X., Pedaletti, G., Peresano, M., Perri, L., Persic, M., Poutanen, J., Moroni, P. G. Prada, Prandini, E., Puljak, I., Reichardt, I., Ribo, M., Rico, J., Garcia, J. Rodriguez, Saito, T., Schroeder, S., Schultz, C., Schweizer, T., Sillanpaa, A., Sitarek, J., Snidaric, I., Sobczynska, D., Stamerra, A., Steinbring, T., Strzys, M., Suric, T., Takalo, L., Tavecchio, F., Temnikov, P., Terzic, 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., Collaboration, R. Zanin VERITAS, Abeysekara, A. U., Archambault, S., Archer, A., Benbow, W., Bird, R., Bourbeau, E., Buchovecky, M., Bugaev, V., Byrum, K., Cardenzana, J. V, Cerruti, M., Ciupik, L., Connolly, M. P., Cui, W., Dickinson, H. J., Dumm, J., Eisch, J. D., Errando, M., Falcone, A., Feng, Q., Finley, J. P., Fleischhack, H., Flinders, A., Fortson, L., Furniss, A., Gillanders, G. H., Griffin, S., Grube, J., Hutten, M., Haakansson, N., Hervet, O., Holder, J., Humensky, T. B., Johnson, C. A., Kaaret, P., Kar, P., Kelley-Hoskins, N., Kertzman, M., Kieda, D., Krause, M., Krennrich, F., Kumar, S., Lang, M. J., Maier, G., McArthur, S., McCann, A., Moriarty, P., Mukherjee, R., Nguyen, T., Nieto, D., O'Brien, S., Ong, R. A., Otte, A. N., Park, N., Pohl, M., Popkow, A., Pueschel, E., Quinn, J., Ragan, K., Reynolds, P. T., Richards, G. T., Roache, E., Rulten, C., Sadeh, I., Santander, M., Sembroski, G. H., Shahinyan, K., Staszak, D., Telezhinsky, I., Tucci, J. V., Tyler, J., Wakely, S. P., Weinstein, A., Wilcox, P., Wilhelm, A., Williams, D. A., and Zitzer, B.
Subjects: High Energy Physics - Experiment, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, Physics - Instrumentation and Detectors
Abstract: We describe and report the status of a neutrino-triggered program in IceCube that generates real-time alerts for gamma-ray follow-up observations by atmospheric-Cherenkov telescopes (MAGIC and VERITAS). While IceCube is capable of monitoring the whole sky continuously, high-energy gamma-ray telescopes have restricted fields of view and in general are unlikely to be observing a potential neutrino-flaring source at the time such neutrinos are recorded. The use of neutrino-triggered alerts thus aims at increasing the availability of simultaneous multi-messenger data during potential neutrino flaring activity, which can increase the discovery potential and constrain the phenomenological interpretation of the high-energy emission of selected source classes (e.g. blazars). The requirements of a fast and stable online analysis of potential neutrino signals and its operation are presented, along with first results of the program operating between 14 March 2012 and 31 December 2015., Comment: accepted for publication in JINST
Published: 2016
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25. A Search for Very High-Energy Gamma Rays from the Missing Link Binary Pulsar J1023+0038 with VERITAS

Author: Aliu, E., Archambault, S., Archer, A., Benbow, W., Bird, R., Biteau, J., Buchovecky, M., Buckley, J. H., Bugaev, V., Byrum, K., Cardenzana, J. V, Cerruti, M., Chen, X., Ciupik, L., Connolly, M. P., Cui, W., Dickinson, H. J., Eisch, J. D., Falcone, A., Feng, Q., Finley, J. P., Fleischhack, H., Flinders, A., Fortin, P., Fortson, L., Furniss, A., Gillanders, G. H., Griffin, S., Grube, J., Gyuk, G., Hütten, M., Håkansson, N., Holder, J., Humensky, T. B., Johnson, C. A., Kaaret, P., Kar, P., Kelley-Hoskins, N., Kertzman, M., Kieda, D., Krause, M., Lang, M. J., Loo, A., Maier, G., McArthur, S., McCann, A., Meagher, K., Moriarty, P., Mukherjee, R., Nguyen, T., Nieto, D., de Bhróithe, A. O'Faoláin, Ong, R. A., Otte, A. N., Pandel, D., Park, N., Pelassa, V., Petrashyk, A., Pohl, M., Popkow, A., Pueschel, E., Quinn, J., Ragan, K., Reynolds, P. T., Richards, G. T., Roache, E., Rulten, C., Santander, M., Sembroski, G. H., Shahinyan, K., Smith, A. W., Staszak, D., Telezhinsky, I., Tucci, J. V., Tyler, J., Varlotta, A., Vincent, S., Wakely, S. P., Weiner, O. M., Weinstein, A., Wilhelm, A., Williams, D. A., Zitzer, B., Chernyakova, M., and Roberts, M.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
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., Comment: 7 pages, 3 figures, accepted for publication in ApJ
Published: 2016
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26. Discovery of Very High Energy Gamma Rays from 1ES 1440+122

Author: VERITAS Collaboration, Archambault, S., Archer, A., Barnacka, A., Behera, B., Beilicke, M., Benbow, W., Berger, K., Bird, R., Boettcher, M., Buckley, J. H., Bugaev, V., Cardenzana, J. V, Cerruti, M., Chen, X., Christiansen, J. L., Ciupik, L., Collins-Hughes, E., Connolly, M. P., Cui, W., Dickinson, H. J., Dumm, J., Eisch, J. D., Errando, M., Falcone, A., Federici, S., Feng, Q., Finley, J. P., Fleischhack, H., Fortson, L., Furniss, A., Gillanders, G. H., Godambe, S., Griffin, S., Griffiths, S. T., Grube, J., Gyuk, G., Haakansson, N., Hanna, D., Holder, J., Hughes, G., Johnson, C. A., Kaaret, P., Kar, P., Kertzman, M., Khassen, Y., Kieda, D., Krawczynski, H., Kumar, S., Lang, M. J., Madhavan, A. S, Maier, G., McArthur, S., McCann, A., Meagher, K., Millis, J., Moriarty, P., Nelson, T., Nieto, D., de Bhroithe, A. O'Faolain, Ong, R. A., Otte, A. N., Park, N., Perkins, J. S., Pohl, M., Popkow, A., Prokoph, H., Pueschel, E., Quinn, J., Ragan, K., Rajotte, J., Reyes, L. C., Reynolds, P. T., Richards, G. T., Roache, E., Sembroski, G. H., Shahinyan, K., Smith, A. W., Staszak, D., Sweeney, K, Telezhinsky, I., Tucci, J. V., Tyler, J., Varlotta, A., Vassiliev, V. V., Wakely, S. P., Welsing, R., Wilhelm, A., Williams, D. A., and Zitzer, B.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
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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27. Very High Energy outburst of Markarian 501 in May 2009

Author: Aliu, E., Archambault, S., Archer, A., Arlen, T., Aune, T., Barnacka, A., Behera, B., Beilicke, M., Benbow, W., Berger, K., Bird, R., Bouvier, A., Böttcher, M., Buchovecky, M., Buckley, J. H., Bugaev, V., Cardenzana, J. V, Cerruti, M., Cesarini, A., Chen, X., Ciupik, L., Collins-Hughes, E., Connolly, M. P., Cui, W., Dumm, J., Eisch, J. D., Falcone, A., Federici, S., Feng, Q., Finley, J. P., Fleischhack, H., Fortin, P., Fortson, L., Furniss, A., Galante, N., Gall, D., Gillanders, G. H., Griffin, S., Griffiths, S. T., Grube, J., Gyuk, G., Hütten, M., Håkansson, N., Holder, J., Hughes, G., Humensky, T. B., Johnson, C. A., Kaaret, P., Kar, P., Kelley-Hoskins, N., Kertzman, M., Khassen, Y., Kieda, D., Krause, M., Krawczynski, H., Krennrich, F., Lang, M. J., Madhavan, A. S, Maier, G., McArthur, S., McCann, A., Meagher, K., Millis, J., Moriarty, P., Mukherjee, R., Nieto, D., de Bhróithe, A. O'Faoláin, Ong, R. A., Orr, M., Otte, A. N., Pandel, D., Park, N., Pelassa, V., Perkins, J. S., Pichel, A., Pohl, M., Popkow, A., Quinn, J., Ragan, K., Reyes, L. C., Reynolds, P. T., Roache, E., Rousselle, J., Rovero, A. C., Saxon, D. B., Sembroski, G. H., Shahinyan, K., Sheidaei, F., Skole, C., Smith, A. W., Staszak, D., Telezhinsky, I., Theiling, M., Todd, N. W., Tucci, J. V., Tyler, J., Varlotta, A., Vassiliev, V. V., Vincent, S., Wakely, S. P., Weiner, O. M., Weinstein, A., Welsing, R., Wilhelm, A., Williams, D. A., Zitzer, B., Baring, M. G., Gónzalez, J. Becerra, Cillis, A. N., Horan, D., and Paneque, D.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: The very high energy (VHE; E $>$ 100 GeV) blazar Markarian 501 was observed between April 17 and May 5 (MJD 54938--54956), 2009, as part of an extensive multi-wavelength campaign from radio to VHE. Strong VHE $\gamma$-ray activity was detected on May 1st with Whipple and VERITAS, when the flux (E $>$ 400 GeV) increased to 10 times the pre-flare baseline flux ($3.9{\times 10^{-11}}~{\rm ph~cm^{-2}~s^{-1}}$), reaching five times the flux of the Crab Nebula. This coincided with a decrease in the optical polarization and a rotation of the polarization angle by 15$^{\circ}$. This VHE flare showed a fast flux variation with an increase of a factor $\sim$4 in 25 minutes, and a falling time of $\sim$50 minutes. We present the observations of the quiescent state previous to the flare and of the high state after the flare, focusing on the flux and spectral variability from Whipple, VERITAS, Fermi-LAT, RXTE, and Swift combined with optical and radio data., Comment: 13 pages, 10 figures. Accepted for publication in Astronomy and Astrophysics
Published: 2016
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28. VERITAS and Multiwavelength Observations of the BL Lacertae Object 1ES 1741+196

Author: VERITAS Collaboration, Abeysekara, A. U., Archambault, S., Archer, A., Benbow, W., Bird, R., Biteau, J., Buchovecky, M., Buckley, J. H., Bugaev, V., Byrum, K., Cardenzana, J. V, Cerruti, M., Chen, X., Christiansen, J. L., Ciupik, L., Connolly, M. P., Cui, W., Dickinson, H. J., Dumm, J., Eisch, J. D., Errando, M., Falcone, A., Feng, Q., Finley, J. P., Fleischhack, H., Flinders, A., Fortin, P., Fortson, L., Furniss, A., Gillanders, G. H., Griffin, S., Grube, J., Gyuk, G., Hütten, M., Hanna, D., Holder, J., Humensky, T. B., Johnson, C. A., Kaaret, P., Kar, P., Kelley-Hoskins, N., Kertzman, M., Kieda, D., Krause, M., Krennrich, F., Kumar, S., Lang, M. J., Maier, G., McArthur, S., McCann, A., Meagher, K., Moriarty, P., Mukherjee, R., Nieto, D., O'Brien, S., de Bhróithe, A. O'Faoláin, Ong, R. A., Otte, A. N., Park, N., Pelassa, V., Petrashyk, A., Pohl, M., Popkow, A., Pueschel, E., Quinn, J., Ragan, K., Ratliff, G., Reyes, L. C., Reynolds, P. T., Richards, G. T., Roache, E., Rulten, C., Santander, M., Sembroski, G. H., Shahinyan, K., Smith, A. W., Staszak, D., Telezhinsky, I., Tucci, J. V., Tyler, J., Vincent, S., Wakely, S. P., Weiner, O. M., Weinstein, A., Wilhelm, A., Williams, D. A., and Zitzer, B.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We present results from multiwavelength observations of the BL Lacertae object 1ES 1741+196, including results in the very-high-energy $\gamma$-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 $2.7\pm0.7_{\mathrm{stat}}\pm0.2_{\mathrm{syst}}$. The integral flux above 180 GeV is $(3.9\pm0.8_{\mathrm{stat}}\pm1.0_{\mathrm{syst}})\times 10^{-8}$ m$^{-2}$ s$^{-1}$, corresponding to 1.6% 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., Comment: 8 pages, 5 figures. Accepted for publication in MNRAS
Published: 2016
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29. Upper limits from five years of blazar observations with the VERITAS Cherenkov telescopes

Author: Archambault, S., Archer, A., Benbow, W., Bird, R., Biteau, J., Buchovecky, M., Buckley, J. H., Bugaev, V., Byrum, K., Cerruti, M., Chen, X., Ciupik, L., Connolly, M. P., Cui, W., Eisch, J. D., Errando, M., Falcone, A., Feng, Q., Finley, J. P., Fleischhack, H., Fortin, P., Fortson, L., Furniss, A., Gillanders, G. H., Griffin, S., Grube, J., Gyuk, G., Hütten, M., Hakansson, N., Hanna, D., Holder, J., Humensky, T. B., Johnson, C. A., Kaaret, P., Kar, P., Kelley-Hoskins, N., Kertzman, M., Kieda, D., Krause, M., Krennrich, F., Kumar, S., Lang, M. J., Maier, G., McArthur, S., McCann, A., Meagher, K., Moriarty, P., Mukherjee, R., Nguyen, T., Nieto, D., De Bhróithe, A. O'Faoláin, Ong, R. A., Otte, A. N., Park, N., Perkins, J. S., Pichel, A., Pohl, M., Popkow, A., Pueschel, E., Quinn, J., Ragan, K., Reynolds, P. T., Richards, G. T., Roache, E., Rovero, A. C., Santander, M., Sembroski, G. H., Shahinyan, K., Smith, A. W., Staszak, D., Telezhinsky, I., Tucci, J. V., Tyler, J., Vincent, S., Wakely, S. P., Weiner, O. M., Weinstein, A., Williams, D. A., Zitzer, B., Fumagalli, M., and Prochaska, J. X.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Between the beginning of its full-scale scientific operations in 2007 and 2012, the VERITAS Cherenkov telescope array observed more than 130 blazars; of these, 26 were detected as very-high-energy (VHE; E>100 GeV) {\gamma}-ray sources. In this work, we present the analysis results of a sample of 114 undetected objects. The observations constitute a total live-time of ~570 hours. The sample includes several unidentified Fermi-Large Area Telescope (LAT) sources (located at high Galactic latitude) as well as all the sources from the second Fermi-LAT catalog which are contained within the field of view of the VERITAS observations. We have also performed optical spectroscopy measurements in order to estimate the redshift of some of these blazars that do not have a spectroscopic distance estimate. We present new optical spectra from the Kast instrument on the Shane telescope at the Lick observatory for 18 blazars included in this work, which allowed for the successful measurement or constraint on the redshift of four of them. For each of the blazars included in our sample we provide the flux upper limit in the VERITAS energy band. We also study the properties of the significance distributions and we present the result of a stacked analysis of the data-set, which shows a 4 {\sigma} excess., Comment: 22 pages; accepted for publication in The Astronomical Journal
Published: 2016
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30. A Search for Brief Optical Flashes Associated with the SETI Target KIC 8462852

Author: Abeysekara, A. U., Archambault, S., Archer, A., Benbow, W., Bird, R., Buchovecky, M., Buckley, J. H., Byrum, K., Cardenzana, J. V, Cerruti, M., Chen, X., Christiansen, J. L., Ciupik, L., Cui, W., Dickinson, H. J., Eisch, J. D., Errando, M., Falcone, A., Fegan, D. J., Feng, Q., Finley, J. P., Fleischhack, H., Fortin, P., Fortson, L., Furniss, A., Gillanders, G. H., Griffin, S., Grube, J., Gyuk, G., Huetten, M., Hakansson, N., Hanna, D., Holder, J., Humensky, T. B., Johnson, C. A., Kaaret, P., Kar, P., Kelley-Hoskins, N., Kertzman, M., Kieda, D., Krause, M., Krennrich, F., Kumar, S., Lang, M. J., Lin, T. T. Y., Maier, G., McArthur, S., McCann, A., Meagher, K., Moriarty, P., Mukherjee, R., Nieto, D., O'Brien, S., de Bhroithe, A. O'Faolain, Ong, R. A., Otte, A. N., Park, N., Perkins, J. S., Petrashyk, A., Pohl, M., Popkow, A., Pueschel, E., Quinn, J., Ragan, K., Ratliff, G., Reynolds, P. T., Richards, G. T., Roache, E., Santander, M., Sembroski, G. H., Shahinyan, K., Staszak, D., Telezhinsky, I., Tucci, J. V., Tyler, J., Vincent, S., Wakely, S. P., Weiner, O. M., Weinstein, A., Williams, D. A., and Zitzer, B.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Solar and Stellar Astrophysics
Abstract: The F-type star KIC 8462852 has recently been identified as an exceptional target for SETI (search for extraterrestrial intelligence) observations. We describe an analysis methodology for optical SETI, which we have used to analyse 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 photon per 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., Comment: Accepted for publication in ApJ Letters. Fixed a minor error in the title
Published: 2016
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31. Exceptionally bright TeV flares from the binary LS I +61$^\circ$ 303

Author: VERITAS Collaboration, Archambault, S., Archer, A., Aune, T., Barnacka, A., Benbow, W., Bird, R., Buchovecky, M., Buckley, J. H., Bugaev, V., Byrum, K., Cardenzana, J. V., Cerruti, M., Chen, X., Ciupik, L., Collins-Hughes, E., Connolly, M. P., Cui, W., Dickinson, H. J., Dumm, J., Eisch, J. D., Falcone, A., Feng, Q., Finley, J. P., Fleischhack, H., Flinders, A., Fortin, P., Fortson, L., Furniss, A., Gillanders, G. H., Griffin, S., Grube, J., Gyuk, G., Huetten, M., Hakansson, N., Hanna, D., Holder, J., Humensky, T. B., Johnson, C. A., Kaaret, P., Kar, P., Kelley-Hoskins, N., Kertzman, M., Khassen, Y., Kieda, D., Krause, M., Krennrich, F., Kumar, S., Lang, M. J., Maier, G., McArthur, S., McCann, A., Meagher, K., Millis, J., Moriarty, P., Mukherjee, R., Nieto, D., O'Brien, S., de Bhroithe, A. O'Faolain, Ong, R. A., Otte, A. N., Pandel, D., Park, N., Pelassa, V., Pohl, M., Popkow, A., Pueschel, E., Quinn, J., Ragan, K., Reynolds, P. T., Richards, G. T., Roache, E., Rousselle, J., Rulten, C., Santander, M., Sembroski, G. H., Shahinyan, K., Smith, A. W., Staszak, D., Telezhinsky, I., Tucci, J. V., Tyler, J., Vincent, S., Wakely, S. P., Weiner, O. M., Weinstein, A., Wilhelm, A., Williams, D. A., and Zitzer, B.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: The TeV binary system LS I +61$^\circ$ 303 is known for its regular, non-thermal emission pattern which traces the orbital period of the compact object in its 26.5 day orbit around its B0 Ve star companion. The system typically presents elevated TeV emission around apastron passage with flux levels between 5% and 15% of the steady flux from the Crab Nebula (> 300 GeV). In this article, VERITAS observations of LS I +61$^\circ$ 303 taken in late 2014 are presented, during which bright TeV flares around apastron at flux levels peaking above 30% of the Crab Nebula flux were detected. This is the brightest such activity from this source ever seen in the TeV regime. The strong outbursts have rise and fall times of less than a day. The short timescale of the flares, in conjunction with the observation of 10 TeV photons from LS I +61$^\circ$ 303 during the flares, provides constraints on the properties of the accelerator in the source., Comment: 9 pages, 2 figures. Accepted for publication by ApJL
Published: 2016
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32. Gamma rays from the quasar PKS 1441+25: story of an escape

Author: Abeysekara, A. U., Archambault, S., Archer, A., Aune, T., Barnacka, A., Benbow, W., Bird, R., Biteau, J., Buckley, J. H., Bugaev, V., Cardenzana, J. V, Cerruti, M., Chen, X., Christiansen, J. L., Ciupik, L., Connolly, M. P., Coppi, P., Cui, W., Dickinson, H. J., Dumm, J., Eisch, J. D., Errando, M., Falcone, A., Feng, Q., Finley, J. P., Fleischhack, H., Flinders, A., Fortin, P., Fortson, L., Furniss, A., Gillanders, G. H., Griffin, S., Grube, J., Gyuk, G., Hütten, M., Håkansson, N., Hanna, D., Holder, J., Humensky, T. B., Johnson, C. A., Kaaret, P., Kar, P., Kelley-Hoskins, N., Khassen, Y., Kieda, D., Krause, M., Krennrich, F., Kumar, S., Lang, M. J., Maier, G., McArthur, S., McCann, A., Meagher, K., Moriarty, P., Mukherjee, R., Nieto, D., de Bhróithe, A. O'Faoláin, Ong, R. A., Otte, A. N., Park, N., Perkins, J. S., Petrashyk, A., Pohl, M., Popkow, A., Pueschel, E., Quinn, J., Ragan, K., Ratliff, G., Reynolds, P. T., Richards, G. T., Roache, E., Rousselle, J., Santander, M., Sembroski, G. H., Shahinyan, K., Smith, A. W., Staszak, D., Telezhinsky, I., Todd, N. W., Tucci, J. V., Tyler, J., Vassiliev, V. V., Vincent, S., Wakely, S. P., Weiner, O. M., Weinstein, A., Wilhelm, A., Williams, D. A., Zitzer, B., Smith, P. S., Holoien, T. W. -S., Prieto, J. L., Kochanek, C. S., Stanek, K. Z., Shappee, B., Hovatta, T., Max-Moerbeck, W., Pearson, T. J., Reeves, R. A., Richards, J. L., Readhead, A. C. S., Madejski, G. M., Djorgovski, S. G., Drake, A. J., Graham, M. J., and Mahabal, A.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: 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 April 2015, 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., Comment: 7 pages, 3 figures, published in ApJ Letters 815, L22 (2015)
Published: 2015
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33. Multiwavelength Study of Quiescent States of Mrk 421 with Unprecedented Hard X-Ray Coverage Provided by NuSTAR in 2013

Author: Baloković, M., Paneque, D., Madejski, G., Furniss, A., Chiang, J., team, the NuSTAR, Ajello, M., Alexander, D. M., Barret, D., Blandford, R., Boggs, S. E., Christensen, F. E., Craig, W. W., Forster, K., Giommi, P., Grefenstette, B. W., Hailey, C. J., Harrison, F. A., Hornstrup, A., Kitaguchi, T., Koglin, J. E., Madsen, K. K., Mao, P. H., Miyasaka, H., Mori, K., Perri, M., Pivovaroff, M. J., Puccetti, S., Rana, V., Stern, D., Tagliaferri, G., Urry, C. M., Westergaard, N. J., Zhang, W. W., Zoglauer, A., collaboration, the VERITAS, Archambault, S., Archer, A. A., Barnacka, A., Benbow, W., Bird, R., Buckley, J., Bugaev, V., Cerruti, M., Chen, X., Ciupik, L., Connolly, M. P., Cui, W., Dickinson, H. J., Dumm, J., Eisch, J. D., Falcone, A., Feng, Q., Finley, J. P., Fleischhack, H., Fortson, L., Griffin, S., Griffiths, S. T., Grube, J., Gyuk, G., Huetten, M., Haakansson, N., Holder, J., Humensky, T. B., Johnson, C. A., Kaaret, P., Kertzman, M., Khassen, Y., Kieda, D., Krause, M., Krennrich, F., Lang, M. J., Maier, G., McArthur, S., Meagher, K., Moriarty, P., Nelson, T., Nieto, D., Ong, R. A., Park, N., Pohl, M., Popkow, A., Pueschel, E., Reynolds, P. T., Richards, G. T., Roache, E., Santander, M., Sembroski, G. H., Shahinyan, K., Smith, A. W., Staszak, D., Telezhinsky, I., Todd, N. W., Tucci, J. V., Tyler, J., Vincent, S., Weinstein, A., Wilhelm, A., Williams, D. A., Zitzer, B., collaboration, the MAGIC, Ahnen, M. L., Ansoldi, S., Antonelli, L. A., Antoranz, P., Babic, A., Banerjee, B., Bangale, P., de Almeida, U. Barres, Barrio, J., González, J. Becerra, Bednarek, W., Bernardini, E., Biasuzzi, B., Biland, A., Blanch, O., Bonnefoy, S., Bonnoli, G., Borracci, F., Bretz, T., Carmona, E., 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., Wilhelmi, E. D. de Oña, Mendez, C. Delgado, Di Pierro, F., Prester, D. Dominis, Dorner, D., Doro, M., Einecke, S., Elsaesser, D., Fernández-Barral, A., Fidalgo, D., Fonseca, M. V., Font, L., Frantzen, K., Fruck, C., Galindo, D., López, R. J. García, Garczarczyk, M., Terrats, D. Garrido, Gaug, M., Giammaria, P., Eisenacher, D., Godinović, N., Muñoz, A. González, Guberman, 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, F., López, M., López-Coto, R., López-Oramas, A., Lorenz, E., Majumdar, P., Makariev, M., Mallot, K., Maneva, G., Manganaro, M., Mannheim, K., Maraschi, L., Marcote, B., Mariotti, M., Martínez, 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., Orito, R., Overkemping, A., Paiano, S., Palacio, S., Palatiello, M., Paoletti, R., Paredes, J. M., Paredes-Fortuny, X., Persic, M., Poutanen, J., Moroni, P. G. Prada, Prandini, E., Puljak, I., Rhode, W., Ribó, M., Rico, J., Garcia, J. Rodriguez, Saito, T., Satalecka, K., Scapin, V., Schultz, C., Schweizer, T., Shore, S. N., Sillanpää, A., Sitarek, J., Snidaric, I., Sobczynska, D., Stamerra, A., Steinbring, T., Strzys, M., Takalo, L. O., Takami, H., Tavecchio, F., Temnikov, P., Terzić, T., Tescaro, D., Teshima, M., Thaele, J., Torres, D. F., Toyama, T., Treves, A., Verguilov, V., Vovk, I., Ward, J. E., Will, M., Wu, M. H., Zanin, R., collaborators, external, Perkins, J., Verrecchia, F., Leto, C., Böttcher, M., Villata, M., Raiteri, C. M., Acosta-Pulido, J. A., Bachev, R., Berdyugin, A., Blinov, D. A., Carnerero, M. I., Chen, W. P., Chinchilla, P., Damljanovic, G., Eswaraiah, C., Grishina, T. S., Ibryamov, S., Jordan, B., Jorstad, S. G., Joshi, M., Kopatskaya, E. N., Kurtanidze, O. M., Kurtanidze, S. O., Larionova, E. G., Larionova, L. V., Larionov, V. M., Latev, G., Lin, H. C., Marscher, A. P., Mokrushina, A. A., Morozova, D. A., Nikolashvili, M. G., Semkov, E., Strigachev, A., Troitskaya, Yu. V., Troitsky, I. S., Vince, O., Barnes, J., Güver, T., Moody, J. W., Sadun, A. C., Sun, S., Hovatta, T., Richards, J. L., Max-Moerbeck, W., Readhead, A. C., Lähteenmäki, A., Tornikoski, M., Tammi, J., Ramakrishnan, V., Reinthal, R., Angelakis, E., Fuhrmann, L., Myserlis, I., Karamanavis, V., Sievers, A., Ungerechts, H., and Zensus, J. A.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We present coordinated multiwavelength observations of the bright, nearby BL Lac object Mrk 421 taken in 2013 January-March, involving GASP-WEBT, Swift, NuSTAR, Fermi-LAT, MAGIC, VERITAS, and other collaborations and instruments, providing data from radio to very-high-energy (VHE) gamma-ray bands. NuSTAR yielded previously unattainable sensitivity in the 3-79 keV range, revealing that the spectrum softens when the source is dimmer until the X-ray spectral shape saturates into a steep power law with a photon index of approximately 3, with no evidence for an exponential cutoff or additional hard components up to about 80 keV. For the first time, we observed both the synchrotron and the inverse-Compton peaks of the spectral energy distribution (SED) simultaneously shifted to frequencies below the typical quiescent state by an order of magnitude. The fractional variability as a function of photon energy shows a double-bump structure which relates to the two bumps of the broadband SED. In each bump, the variability increases with energy which, in the framework of the synchrotron self-Compton model, implies that the electrons with higher energies are more variable. The measured multi-band variability, the significant X-ray-to-VHE correlation down to some of the lowest fluxes ever observed in both bands, the lack of correlation between optical/UV and X-ray flux, the low degree of polarization and its significant (random) variations, the short estimated electron cooling time, and the significantly longer variability timescale observed in the NuSTAR light curves point toward in-situ electron acceleration, and suggest that there are multiple compact regions contributing to the broadband emission of Mrk 421 during low-activity states., Comment: 32 pages, 14 figures; accepted for publication in ApJ
Published: 2015
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34. In-situ measurements of whole-dish reflectivity for VERITAS

Author: Archambault, S., Chernitsky, G., Griffin, S., and Hanna, D.
Published: 2021
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35. VERITAS Collaboration Contributions to the 34th International Cosmic Ray Conference

Author: The VERITAS Collaboration, Abeysekara, A. U., Archambault, S., Archer, A., Barnacka, A., Benbow, W., Bird, R., Biteau, J., Buchovecky, M., Buckley, J. H., Bugaev, V., Byrum, K., Cardenzana, J. V, Cerruti, M., Chen, X., Christiansen, J. L., Ciupik, L., Collins-Hughes, E., Connolly, M. P., Coppi, P., Cui, W., Dwarkadas, V. V., Eisch, J. D., Errando, M., Falcone, A., Feng, Q., Alonso, M. Fernandez, Finley, J. P., Fleischhack, H., Flinders, A., Fortin, P., Fortson, L., Furniss, A., Gillanders, G. H., Griffin, S., Griffiths, S. T., Gyuk, G., Hütten, M., Hanna, D., Holder, J., Humensky, T. B., Johnson, C. A., Kaaret, P., Kar, P., Kertzman, M., Khassen, Y., Kieda, D., Krause, M., Krennrich, F., Kumar, S., Lang, M. J., Maier, G., McArthur, S., McCann, A., Meagher, K., Moriarty, P., Mukherjee, R., Nguyen, T., Nieto, D., de Bhróithe, A. O'Faoláin, Ong, R. A., Otte, A. N., Pandel, D., Park, N., Pelassa, V., Perkins, J. S., Petrashyk, A., Pohl, M., Popkow, A., Pueschel, E., Quinn, J., Ragan, K., Reynolds, P. T., Richards, G. T., Roache, E., Rovero, A. C., Santander, M., Schlenstedt, S., Sembroski, G. H., Shahinyan, K., Smith, A. W., Staszak, D., Telezhinsky, I., Tucci, J. V., Tyler, J., Vassiliev, V. V., Vincent, S., Wakely, S. P., Weiner, O. M., Weinstein, A., Wilhelm, A., Williams, D. A., and Zitzer, B.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Compilation of papers presented by the VERITAS Collaboration at the 34th International Cosmic Ray Conference (ICRC), held July 30 through August 6, 2015 in The Hague, The Netherlands., Comment: 1 html page. 2015 ICRC, The Hague, The Netherlands. A full list of author affiliations can be found at this link: http://veritas.sao.arizona.edu/conferences/authors?icrc2015
Published: 2015

36. Science Highlights from VERITAS

Author: Staszak, D., Abeysekara, A. U., Archambault, S., Archer, A., Barnacka, A., Benbow, W., Bird, R., Biteau, J., Buchovecky, M., Buckley, J. H., Bugaev, V., Byrum, K., Cardenzana, J. V, Cerruti, M., Chen, X., Christiansen, J. L., Ciupik, L., Collins-Hughes, E., Connolly, M. P., Coppi, P., Cui, W., Dwarkadas, V. V., Eisch, J. D., Errando, M., Falcone, A., Feng, Q., Alonso, M. Fernandez, Finley, J. P., Fleischhack, H., Flinders, A., Fortin, P., Fortson, L., Furniss, A., Gillanders, G. H., Griffin, S., Griffiths, S. T., Gyuk, G., Hütten, M., Hanna, D., Holder, J., Humensky, T. B., Johnson, C. A., Kaaret, P., Kar, P., Kertzman, M., Khassen, Y., Kieda, D., Krause, M., Krennrich, F., Kumar, S., Lang, M. J., Maier, G., McArthur, S., McCann, A., Meagher, K., Moriarty, P., Mukherjee, R., Nguyen, T., Nieto, D., de Bhróithe, A. O'Faoláin, Ong, R. A., Otte, A. N., Pandel, D., Park, N., Pelassa, V., Perkins, J. S., Pohl, M., Popkow, A., Pueschel, E., Quinn, J., Ragan, K., Reynolds, P. T., Richards, G. T., Roache, E., Rovero, A. C., Santander, M., Schlenstedt, S., Sembroski, G. H., Shahinyan, K., Smith, A. W., Telezhinsky, I., Tucci, J. V., Tyler, J., Vassiliev, V. V., Vincent, S., Wakely, S. P., Weiner, O. M., Weinstein, A., Wilhelm, A., Williams, D. A., and Zitzer, B.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: The Very Energetic Radiation Imaging Telescope Array System (VERITAS) is a ground-based array located at the Fred Lawrence Whipple Observatory in southern Arizona and is one of the world's most sensitive gamma-ray instruments at energies of 85 GeV to $>$30 TeV. VERITAS has a wide scientific reach that includes the study of extragalactic and Galactic objects as well as the search for astrophysical signatures of dark matter and the measurement of cosmic rays. In this paper, we will summarize the current status of the VERITAS observatory and present some of the scientific highlights from the last two years, focusing in particular on those results shown at the 2015 ICRC in The Hague, Netherlands., Comment: To appear in the Proceedings of the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherlands
Published: 2015

37. VERITAS detection of $\gamma$-ray flaring activity from the BL Lac object 1ES 1727+502 during bright moonlight observations

Author: Archambault, S., Archer, A., Beilicke, M., Benbow, W., Bird, R., Biteau, J., Bouvier, A., Bugaev, V., Cardenzana, J. V, Cerruti, M., Chen, X., Ciupik, L., Connolly, M. P., Cui, W., Dickinson, H. J., Dumm, J., Eisch, J. D., Errando, M., Falcone, A., Feng, Q., Finley, J. P., Fleischhack, H., Fortin, P., Fortson, L., Furniss, A., Gillanders, G. H., Griffin, S., Griffiths, S. T., Grube, J., Gyuk, G., Håkansson, N., Hanna, D., Holder, J., Humensky, T. B., Johnson, C. A., Kaaret, P., Kar, P., Kertzman, M., Khassen, Y., Kieda, D., Krause, M., Krennrich, F., Kumar, S., Lang, M. J., Maier, G., McArthur, S., McCann, A., Meagher, K., Millis, J., Moriarty, P., Mukherjee, R., Nieto, D., de Bhróithe, A. O'Faoláin, Ong, R. A., Otte, A. N., Park, N., Pohl, M., Popkow, A., Prokoph, H., Pueschel, E., Quinn, J., Ragan, K., Reyes, L. C., Reynolds, P. T., Richards, G. T., Roache, E., Santander, M., Sembroski, G. H., Shahinyan, K., Smith, A. W., Staszak, D., Telezhinsky, I., Tucci, J. V., Tyler, J., Varlotta, A., Vincent, S., Wakely, S. P., Weinstein, A., Welsing, R., Wilhelm, A., Williams, D. A., Zitzer, B., and Hughes, Z. D.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: During moonlit nights, observations with ground-based Cherenkov telescopes at very high energies (VHE, $E>100$ GeV) are constrained since the photomultiplier tubes (PMTs) in the telescope camera are extremely sensitive to the background moonlight. Observations with the VERITAS telescopes in the standard configuration are performed only with a moon illumination less than 35$\%$ of full moon. Since 2012, the VERITAS collaboration has implemented a new observing mode under bright moonlight, by either reducing the voltage applied to the PMTs (reduced-high-voltage configuration, RHV), or by utilizing UV-transparent filters. While these operating modes result in lower sensitivity and increased energy thresholds, the extension of the available observing time is useful for monitoring variable sources such as blazars and sources requiring spectral measurements at the highest energies. In this paper we report the detection of $\gamma$-ray flaring activity from the BL Lac object 1ES 1727+502 during RHV observations. This detection represents the first evidence of VHE variability from this blazar. The integral flux is $(1.1\pm0.2)\times10^{-11}\mathrm{cm^{-2}s^{-1}}$ above 250 GeV, which is about five times higher than the low-flux state. The detection triggered additional \veritas\ observations during standard dark-time. Multiwavelength observations with the FLWO 48" telescope, and the Swift and Fermi satellites are presented and used to produce the first spectral energy distribution (SED) of this object during $\gamma$-ray flaring activity. The SED is then fitted with a standard synchrotron-self-Compton model, placing constraints on the properties of the emitting region and of the acceleration mechanism at the origin of the relativistic particle population in the jet., Comment: 11 pages, 3 figures, accepted for publication in ApJ
Published: 2015
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38. The 2009 multiwavelength campaign on Mrk 421: Variability and correlation studies

Author: MAGIC Collaboration, Aleksić, J., Ansoldi, S., Antonelli, L. A., Antoranz, P., Babic, A., Bangale, P., de Almeida, U. Barres, Barrio, J. A., González, J. Becerra, Bednarek, W., Berger, K., Bernardini, E., Biland, A., Blanch, O., Bock, R. K., Bonnefoy, S., Bonnoli, G., Borracci, F., Bretz, T., Carmona, E., Carosi, A., Fidalgo, D. Carreto, Colin, P., Colombo, E., Contreras, J. L., Cortina, J., Covino, S., Da Vela, P., Dazzi, F., De Angelis, A., De Caneva, G., De Lotto, B., Mendez, C. Delgado, Doert, M., Domínguez, A., Prester, D. Dominis, Dorner, D., Doro, M., Einecke, S., Eisenacher, D., Elsaesser, D., Farina, E., Ferenc, D., Fonseca, M. V., Font, L., Frantzen, K., Fruck, C., López, R. J. García, Garczarczyk, M., Terrats, D. Garrido, Gaug, M., Giavitto, G., Godinović, N., noz, A. González Mu\, Gozzini, S. R., Hadamek, A., Hadasch, D., Herrero, A., Hildebrand, D., Hose, J., Hrupec, D., Idec, W., Kadenius, V., Kellermann, H., Knoetig, M. L., Krause, J., Kushida, J., La Barbera, A., Lelas, D., Lewandowska, N., Lindfors, E., Longo, F., Lombardi, S., López, M., López-Coto, R., López-Oramas, A., Lorenz, E., Lozano, I., Makariev, M., Mallot, K., Maneva, G., Mankuzhiyil, N., Mannheim, K., Maraschi, L., Marcote, B., Mariotti, M., Martínez, M., Mazin, D., Menzel, U., Meucci, M., Miranda, J. M., Mirzoyan, R., Moralejo, A., Munar-Adrover, P., Nakajima, D., Niedzwiecki, A., Nilsson, K., Nowak, N., Orito, R., Overkemping, A., Paiano, S., Palatiello, M., Paneque, D., Paoletti, R., Paredes, J. M., Paredes-Fortuny, X., Partini, S., Persic, M., Prada, F., Moroni, P. G. Prada, Prandini, E., Preziuso, S., Puljak, I., Reinthal, R., Rhode, W., Ribó, M., Rico, J., Garcia, J. Rodriguez, Rügamer, S., Saggion, A., Saito, K., Salvati, M., Satalecka, K., Scalzotto, V., Scapin, V., Schultz, C., Schweizer, T., Shore, S. N., Sillanpää, A., Sitarek, J., Snidaric, I., Sobczynska, D., Spanier, F., Stamatescu, V., Stamerra, A., Steinbring, T., Storz, J., Sun, S., Surić, T., Takalo, L., Tavecchio, F., Temnikov, P., Terzić, T., Tescaro, D., Teshima, M., Thaele, J., Tibolla, O., Torres, D. F., Toyama, T., Treves, A., Uellenbeck, M., Vogler, P., Wagner, R. M., Zandanel, F., Zanin, R., collaboration, VERITAS, Archambault, S., Behera, B., Beilicke, M., Benbow, W., Bird, R., Buckley, J. H., Bugaev, V., Cerruti, M., Chen, X., Ciupik, L., Collins-Hughes, E., Cui, W., Dumm, J., Eisch, J. D., Falcone, A., Federici, S., Feng, Q., Finley, J. P., Fleischhack, H., Fortin, P., Fortson, L., Furniss, A., Griffin, S., Griffiths, S. T., Grube, J., Gyuk, G., Hanna, D., Holder, J., Hughes, G., Humensky, T. B., Johnson, C. A., Kaaret, P., Kertzman, M., Khassen, Y., Kieda, D., Krawczynski, H., Krennrich, F., Kumar, S., Lang, M. J., Maier, G., McArthur, S., Meagher, K., Moriarty, P., Mukherjee, R., Ong, R. A., Otte, A. N., Park, N., Pichel, A., Pohl, M., Popkow, A., Prokoph, H., Quinn, J., Ragan, K., Rajotte, J., Reynolds, P. T., Richards, G. T., Roache, E., Rovero, A. C., Sembroski, G. H., Shahinyan, K., Staszak, D., Telezhinsky, I., Theiling, M., Tucci, J. V., Tyler, J., Varlotta, A., Wakely, S. P., Weekes, T. C., Weinstein, A., Welsing, R., Wilhelm, A., Williams, D. A., Zitzer, B., collaborators, External, Villata, M., Raiteri, C., Aller, H. D., Aller, M. F., Chen, W. P., Jordan, B., Koptelova, E., Kurtanidze, O. M., Lähteenmäki, A., McBreen, B., Larionov, V. M., Lin, C. S., Nikolashvili, M. G., Angelakis, E., Capalbi, M., nana, A. Carrami\, Carrasco, L., Cassaro, P., Cesarini, A., Fuhrmann, L., Giroletti, M., Hovatta, T., Krichbaum, T. P., Krimm, H. A., Max-Moerbeck, W., Moody, J. W., Maccaferri, G., Mori, Y., Nestoras, I., Orlati, A., Pace, C., Pearson, R., Perri, M., Readhead, A. C. S., Richards, J. L., Sadun, A. C., Sakamoto, T., Tammi, J., Tornikoski, M., Yatsu, Y., and Zook, A.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We performed a 4.5-month multi-instrument campaign (from radio to VHE gamma rays) on Mrk421 between January 2009 and June 2009, which included VLBA, F-GAMMA, GASP-WEBT, Swift, RXTE, Fermi-LAT, MAGIC, and Whipple, among other instruments and collaborations. Mrk421 was found in its typical (non-flaring) activity state, with a VHE flux of about half that of the Crab Nebula, yet the light curves show significant variability at all wavelengths, the highest variability being in the X-rays. We determined the power spectral densities (PSD) at most wavelengths and found that all PSDs can be described by power-laws without a break, and with indices consistent with pink/red-noise behavior. We observed a harder-when-brighter behavior in the X-ray spectra and measured a positive correlation between VHE and X-ray fluxes with zero time lag. Such characteristics have been reported many times during flaring activity, but here they are reported for the first time in the non-flaring state. We also observed an overall anti-correlation between optical/UV and X-rays extending over the duration of the campaign. The harder-when-brighter behavior in the X-ray spectra and the measured positive X-ray/VHE correlation during the 2009 multi-wavelength campaign suggests that the physical processes dominating the emission during non-flaring states have similarities with those occurring during flaring activity. In particular, this observation supports leptonic scenarios as being responsible for the emission of Mrk421 during non-flaring activity. Such a temporally extended X-ray/VHE correlation is not driven by any single flaring event, and hence is difficult to explain within the standard hadronic scenarios. The highest variability is observed in the X-ray band, which, within the one-zone synchrotron self-Compton scenario, indicates that the electron energy distribution is most variable at the highest energies., Comment: Accepted for publication in A&A, 18 pages, 14 figures (v2 has a small modification in the acknowledgments, and also corrects a typo in the field "author" in the metadata)
Published: 2015
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39. A Search for Pulsations from Geminga Above 100 GeV with VERITAS

Author: Aliu, E., Archambault, S., Archer, A., Aune, T., Barnacka, A., Beilicke, M., Benbow, W., Bird, R., Buckley, J. H., Bugaev, V., Byrum, K., Cardenzana, J. V, Cerruti, M., Chen, X., Ciupik, L., Connolly, M. P., Cui, W., Dickinson, H. J., Dumm, J., Eisch, J. D., Errando, M., Falcone, A., Feng, Q., Finley, J. P., Fleischhack, H., Fortin, P., Fortson, L., Furniss, A., Gillanders, G. H., Griffin, S., Griffiths, S. T., Grube, J., Gyuk, G., Hakansson, N., Hanna, D., Holder, J., Humensky, T. B., Johnson, C. A., Kaaret, P., Kar, P., Kertzman, M., Kieda, D., Krennrich, F., Kumar, S., Lang, M. J., Lyutikov, M., Madhavan, A. S, Maier, G., McArthur, S., McCann, A., Meagher, K., Millis, J., Moriarty, P., Mukherjee, R., Nieto, D., de Bhroithe, A. O'Faolain, Ong, R. A., Otte, A. N., Park, N., Pohl, M., Popkow, A., Prokoph, H., Pueschel, E., Quinn, J., Ragan, K., Reyes, L. C., Reynolds, P. T., Richards, G. T., Roache, E., Santander, M., Sembroski, G. H., Shahinyan, K., Smith, A. W., Staszak, D., Telezhinsky, I., Tucci, J. V., Tyler, J., Varlotta, A., Vincent, S., Wakely, S. P., Weinstein, A., Williams, D. A., Zajczyk, A., and Zitzer, B.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We present the results of 71.6 hours of observations of the Geminga pulsar (PSR J0633+1746) with the VERITAS very-high-energy gamma-ray telescope array. Data taken with VERITAS between November 2007 and February 2013 were phase-folded using a Geminga pulsar timing solution derived from data recorded by the XMM-\emph{Newton} and \emph{Fermi}-LAT space telescopes. No significant pulsed emission above 100 GeV is observed, and we report upper limits at the 95% confidence level on the integral flux above 135 GeV (spectral analysis threshold) of 4.0$\times10^{-13}$ s$^{-1}$ cm$^{-2}$ and 1.7$\times10^{-13}$ s$^{-1}$ cm$^{-2}$ for the two principal peaks in the emission profile. These upper limits, placed in context with phase-resolved spectral energy distributions determined from five years of data from the \emph{Fermi}-LAT, constrain possible hardening of the Geminga pulsar emission spectra above $\sim$50 GeV., Comment: 7 pages, 2 figures, 2 tables. Accepted for publication in ApJ
Published: 2014
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40. Unprecedented study of the broadband emission of Mrk 421 during flaring activity in March 2010

Author: The MAGIC Collaboration, Aleksić, J., Ansoldi, S., Antonelli, L. A., Antoranz, P., Babic, A., Bangale, P., de Almeida, U. Barres, Barrio, J. A., González, J. Becerra, Bednarek, W., Bernardini, E., Biasuzzi, B., Biland, A., Blanch, O., Boller, A., Bonnefoy, S., Bonnoli, G., Borracci, F., Bretz, T., Carmona, E., Carosi, A., Colin, P., Colombo, E., Contreras, J. L., Cortina, J., Covino, S., Da Vela, P., Dazzi, F., De Angelis, A., De Caneva, G., De Lotto, B., Wilhelmi, E. de Oña, Mendez, C. Delgado, Prester, D. Dominis, Dorner, D., Doro, M., Einecke, S., Eisenacher, D., Elsaesser, D., Fonseca, M. V., Font, L., Frantzen, K., Fruck, C., Galindo, D., López, R. J. García, Garczarczyk, M., Terrats, D. Garrido, Gaug, M., Godinović, N., Muñoz, A. González, Gozzini, S. R., Hadasch, D., Hanabata, Y., Hayashida, M., Herrera, J., Hildebrand, D., Hose, J., Hrupec, D., Hughes, G., Idec, W., Kadenius, V., Kellermann, H., Knoetig, M. L., Kodani, K., Konno, Y., Krause, J., Kubo, H., Kushida, J., La Barbera, A., Lelas, D., Lewandowska, N., Lindfors, E., Lombardi, S., López, M., López-Coto, R., López-Oramas, A., Lorenz, E., Lozano, I., Makariev, M., Mallot, K., Maneva, G., Mankuzhiyil, N., Mannheim, K., Maraschi, L., Marcote, B., Mariotti, M., Martínez, M., Mazin, D., Menzel, U., Miranda, J. M., Mirzoyan, R., Moralejo, A., Munar-Adrover, P., Nakajima, D., Niedzwiecki, A., Nilsson, K., Nishijima, K., Noda, K., Orito, R., Overkemping, A., Paiano, S., Palatiello, M., Paneque, D., Paoletti, R., Paredes, J. M., Paredes-Fortuny, X., Persic, M., Moroni, P. G. Prada, Prandini, E., Puljak, I., Reinthal, R., Rhode, W., Ribó, M., Rico, J., Garcia, J. Rodriguez, Rügamer, S., Saito, T., Saito, K., Satalecka, K., Scalzotto, V., Scapin, V., Schultz, C., Schweizer, T., Sun, S., Shore, S. N., Sillanpää, A., Sitarek, J., Snidaric, I., Sobczynska, D., Spanier, F., Stamatescu, V., Stamerra, A., Steinbring, T., Steinke, B., Storz, J., Strzys, M., Takalo, L., Takami, H., Tavecchio, F., Temnikov, P., Terzić, T., Tescaro, D., Teshima, M., Thaele, J., Tibolla, O., Torres, D. F., Toyama, T., Treves, A., Uellenbeck, M., Vogler, P., Zanin, R., Collaboration, The VERITAS, Archambault, S., Archer, A., Beilicke, M., Benbow, W., Berger, K., Bird, R., Biteau, J., Buckley, J. H., Bugaev, V., Cerruti, M., Chen, X., Ciupik, L., Collins-Hughes, E., Cui, W., Eisch, J. D., Falcone, A., Feng, Q., Finley, J. P., Fortin, P., Fortson, L., Furniss, A., Galante, N., Gillanders, G. H., Griffin, S., Gyuk, G., Håkansson, N., Holder, J., Johnson, C. A., Kaaret, P., Kar, P., Kertzman, M., Kieda, D., Lang, M. J., McArthur, S., McCann, A., Meagher, K., Millis, J., Moriarty, P., Ong, R. A., Otte, A. N., Perkins, J. S., Pichel, A., Pohl, M., Popkow, A., Prokoph, H., Pueschel, E., Ragan, K., Reyes, L. C., Reynolds, P. T., Richards, G. T., Roache, E., Rovero, A. C., Sembroski, G. H., Shahinyan, K., Staszak, D., Telezhinsky, I., Tucci, J. V., Tyler, J., Varlotta, A., Wakely, S. P., Welsing, R., Wilhelm, A., Williams, D. A., Collaborators, External, Buson, S., Finke, J., Villata, M., Raiteri, C., Aller, H. D., Aller, M. F., Cesarini, A., Chen, W. P., Gurwell, M. A., Jorstad, S. G., Kimeridze, G. N., Koptelova, E., Kurtanidze, O. M., Kurtanidze, S. O., Lähteenmäki, A., Larionov, V. M., Larionova, E. G., Lin, H. C., McBreen, B., Moody, J. W., Morozova, D. A., Marscher, A. P., Max-Moerbeck, W., Nikolashvili, M. G., Perri, M., Readhead, A. C. S., Richards, J. L., Ros, J. A., Sadun, A. C., Sakamoto, T., Sigua, L. A., Smith, P. S., Tornikoski, M., Troitsky, I. S., Wehrle, A. E., and Jordan, B.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
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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41. Investigating Broadband Variability of the TeV Blazar 1ES 1959+650

Author: Aliu, E., Archambault, S., Arlen, T., Aune, T., Barnacka, A., Beilicke, M., Benbow, W., Berger, K., Bird, R., Bouvier, A., Buckley, J. H., Bugaev, V., Cerruti, M., Chen, X., Ciupik, L., Collins-Hughes, E., Connolly, M. P., Cui, W., Dumm, J., Eisch, J. D., Falcone, A., Federici, S., Feng, Q., Finley, J. P., Fleischhack, H., Fortin, P., Fortson, L., Furniss, A., Galante, N., Gillanders, G. H., Griffin, S., Griffiths, S. T., Grube, J., Gyuk, G., Hakansson, N., Hanna, D., Holder, J., Hughes, G., Humensky, T. B., Johnson, C. A., Kaaret, P., Kar, P., Kertzman, M., Khassen, Y., Kieda, D., Krawczynski, H., Krennrich, F., Lang, M. J., Madhavan, A. S, Majumdar, P., McArthur, S., McCann, A., Meagher, K., Millis, J., Moriarty, P., Mukherjee, R., Nelson, T., Nieto, D., de Bhroithe, A. O'Faolain, Ong, R. A., Otte, A. N., Park, N., Perkins, J. S., Pohl, M., Popkow, A., Prokoph, H., Quinn, J., Ragan, K., Rajotte, J., Reyes, L. C., Reynolds, P. T., Richards, G. T., Roache, E., Sadun, A., Santander, M., Sembroski, G. H., Shahinyan, K., Sheidaei, F., Smith, A. W., Staszak, D., Telezhinsky, I., Theiling, M., Tyler, J., Varlotta, A., Vassiliev, V. V., Vincent, S., Wakely, S. P., Weekes, T. C., Weinstein, A., Welsing, R., Wilhelm, A., Williams, D. A., Zitzer, B., Böttcher, M., and Fumagalli, M.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We summarize broadband observations of the TeV-emitting blazar 1ES 1959+650, including optical R-band observations by the robotic telescopes Super-LOTIS and iTelescope, UV observations by Swift UVOT, X-ray observations by the Swift X-ray Telescope (XRT), high-energy gamma-ray observations with the Fermi Large Area Telescope (LAT) and very-high-energy (VHE) gamma-ray observations by VERITAS above 315 GeV, all taken between 17 April 2012 and 1 June 2012 (MJD 56034 and 56079). The contemporaneous variability of the broadband spectral energy distribution is explored in the context of a simple synchrotron self Compton (SSC) model. In the SSC emission scenario, we find that the parameters required to represent the high state are significantly different than those in the low state. Motivated by possible evidence of gas in the vicinity of the blazar, we also investigate a reflected-emission model to describe the observed variability pattern. This model assumes that the non-thermal emission from the jet is reflected by a nearby cloud of gas, allowing the reflected emission to re-enter the blob and produce an elevated gamma-ray state with no simultaneous elevated synchrotron flux. The model applied here, although not required to explain the observed variability pattern, represents one possible scenario which can describe the observations. As applied to an elevated VHE state of 66% of the Crab Nebula flux, observed on a single night during the observation period, the reflected-emission scenario does not support a purely leptonic non-thermal emission mechanism. The reflected emission model does, however, predict a reflected photon field with sufficient energy to enable elevated gamma-ray emission via pion production with protons of energies between 10 and 100 TeV., Comment: Accepted by ApJ
Published: 2014
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42. Investigating the TeV Morphology of MGRO J1908+06 with VERITAS

Author: Aliu, E., Archambault, S., Aune, T., Behera, B., Beilicke, M., Benbow, W., Berger, K., Bird, R., Buckley, J. H., Bugaev, V., Cardenzana, J. V, Cerruti, M., Chen, X., Ciupik, L., Collins-Hughes, E., Connolly, M. P., Cui, W., Dumm, J., Dwarkadas, V. V., Errando, M., Falcone, A., Federici, S., Feng, Q., Finley, J. P., Fleischhack, H., Fortin, P., Fortson, L., Furniss, A., Galante, N., Gall, D., Gillanders, G. H., Griffin, S., Griffiths, S. T., Grube, J., Gyuk, G., Hanna, D., Holder, J., Hughes, G., Humensky, T. B., Kaaret, P., Kertzman, M., Khassen, Y., Kieda, D., Krennrich, F., Kumar, S., Lang, M. J., Madhavan, A. S, Maier, G., McCann, A. J., Meagher, K., Millis, J., Moriarty, P., Mukherjee, R., Nieto, D., de Bhroithe, A. O'Faolain, Ong, R. A., Otte, A. N., Pandel, D., Park, N., Pohl, M., Popkow, A., Prokoph, H., Quinn, J., Ragan, K., Rajotte, J., Ratliff, G., Reyes, L. C., Reynolds, P. T., Richards, G. T., Roache, E., Rousselle, J., Sembroski, G. H., Shahinyan, K., Sheidaei, F., Smith, A. W., Staszak, D., Telezhinsky, I., Tsurusaki, K., Tucci, J. V., Tyler, J., Varlotta, A., Vassiliev, V. V., Vincent, S., Wakely, S. P., Ward, J. E., Weinstein, A., Welsing, R., and Wilhelm, A.
Subjects: 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., Comment: To appear in ApJ, 8 pages
Published: 2014
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43. Deep Broadband Observations of the Distant Gamma-ray Blazar PKS 1424+240

Author: Archambault, S., Aune, T., Behera, B., Beilicke, M., Benbow, W., Berger, K., Bird, R., Biteau, J., Bugaev, V., Byrum, K., Cardenzana, J. V, Cerruti, M., Chen, X., Ciupik, L., Connolly, M. P., Cui, W., Dumm, J., Errando, M., Falcone, A., Federici, S., Feng, Q., Finley, J. P., Fleischhack, H., Fortson, L., Furniss, A., Galante, N., Gillanders, G. H., Griffin, S., Griffiths, S. T., Grube, J., Gyuk, G., Hanna, D., Holder, J., Hughes, G., Humensky, T. B., Johnson, C. A., Kaaret, P., Kertzman, M., Khassen, Y., Kieda, D., Krawczynski, H., Krennrich, F., Kumar, S., Lang, M. J., Madhavan, A. S, Maier, G., McCann, A., Meagher, K., Moriarty, P., Mukherjee, R., Nieto, D., de Bhroithe, A. O'Faolain, Ong, R. A., Otte, A. N., Park, N., Pohl, M., Popkow, A., Prokoph, H., Quinn, J., Ragan, K., Rajotte, J., Reyes, L. C., Reynolds, P. T., Richards, G. T., Roache, E., Sembroski, G. H., Shahinyan, K., Staszak, D., Telezhinsky, I., Tucci, J. V., Tyler, J., Varlotta, A., Vassiliev, V. V., Vincent, S., Wakely, S. P., Weinstein, A., Welsing, R., Wilhelm, A., Williams, D. A., Ackermann, M., Ajello, M., Albert, A., Baldini, L., Bastieri, D., Bellazzini, R., Bissaldi, E., Bregeon, J., Buehler, R., Buson, S., Caliandro, G. A., Cameron, R. A., Caraveo, P. A., Cavazzuti, E., Charles, E., Chiang, J., Ciprini, S., Claus, R., Cutini, S., D'Ammando, F., de Angelis, A., de Palma, F., Dermer, C. D., Digel, S. W., Di Venere, L., Drell, P. S., Favuzzi, C., Franckowiak, A., Fusco, P., Gargano, F., Gasparrini, D., Giglietto, N., Giordano, F., Giroletti, M., Grenier, I. A., Guiriec, S., Jogler, T., Kuss, M., Larsson, S., Latronico, L., Longo, F., Loparco, F., Lubrano, P., Madejski, G. M., Mayer, M., Mazziotta, M. N., Michelson, P. F., Mizuno, T., Monzani, M. E., Morselli, A., Murgia, S., Nuss, E., Ohsugi, T., Ormes, J. F., Perkins, J. S., Piron, F., Pivato, G., Raino, S., Razzano, M., Reimer, A., Reimer, O., Ritz, S., Schaal, M., Sgro, C., Siskind, E. J., Spinelli, P., Takahashi, H., Tibaldo, L., Tinivella, M., Troja, E., Vianello, G., Werner, M., and Wood, M.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We present deep VERITAS observations of the blazar PKS 1424+240, along with contemporaneous Fermi Large Area Telescope, Swift X-ray Telescope and Swift UV Optical Telescope data between 2009 February 19 and 2013 June 8. This blazar resides at a redshift of $z\ge0.6035$, displaying a significantly attenuated gamma-ray flux above 100 GeV due to photon absorption via pair-production with the extragalactic background light. We present more than 100 hours of VERITAS observations from three years, a multiwavelength light curve and the contemporaneous spectral energy distributions. The source shows a higher flux of (2.1$\pm0.3$)$\times10^{-7}$ ph m$^{-2}$s$^{-1}$ above 120 GeV in 2009 and 2011 as compared to the flux measured in 2013, corresponding to (1.02$\pm0.08$)$\times10^{-7}$ ph m$^{-2}$s$^{-1}$ above 120 GeV. The measured differential very high energy (VHE; $E\ge100$ GeV) spectral indices are $\Gamma=$3.8$\pm$0.3, 4.3$\pm$0.6 and 4.5$\pm$0.2 in 2009, 2011 and 2013, respectively. No significant spectral change across the observation epochs is detected. We find no evidence for variability at gamma-ray opacities of greater than $\tau=2$, where it is postulated that any variability would be small and occur on longer than year timescales if hadronic cosmic-ray interactions with extragalactic photon fields provide a secondary VHE photon flux. The data cannot rule out such variability due to low statistics., Comment: ApJL accepted March 17, 2014
Published: 2014
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44. A Three-Year Multi-Wavelength Study of the Very High Energy Gamma-ray Blazar 1ES 0229+200

Author: Aliu, E., Archambault, S., Arlen, T., Aune, T., Behera, B., Beilicke, M., Benbow, W., Berger, K., Bird, R., Bouvier, A., Buckley, J. H., Bugaev, V., Byrum, K., Cerruti, M., Chen, X., Ciupik, L., Connolly, M. P., Cui, W., Duke, C., Dumm, J., Errando, M., Falcone, A., Federici, S., Feng, Q., Finley, J. P., Fleischhack, H., Fortin, P., Fortson, L., Furniss, A., Galante, N., Gillanders, G. H., Griffin, S., Griffiths, S. T., Grube, J., Gyuk, G., Hanna, D., Holder, J., Hughes, G., Humensky, T. B., Johnson, C. A., Kaaret, P., Kertzman, M., Khassen, Y., Kieda, D., Krawczynski, H., Krennrich, F., Lang, M. J., Madhavan, A. S, Maier, G., Majumdar, P., McArthur, S., McCann, A., Meagher, K., Millis, J., Moriarty, P., Mukherjee, R., Nieto, D., de Bhroithe, A. O'Faolain, Ong, R. A., Otte, A. N., Park, N., Perkins, J. S., Pohl, M., Popkow, A., Prokoph, H., Quinn, J., Ragan, K., Reyes, L. C., Reynolds, P. T., Richards, G. T., Roache, E., Sembroski, G. H., Smith, A. W., Staszak, D., Telezhinsky, I., Theiling, M., Varlotta, A., Vassiliev, V. V., Vincent, S., Wakely, S. P., Weekes, T. C., Weinstein, A., Welsing, R., Williams, D. A., Zajczyk, A., and Zitzer, B.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
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., Comment: Accepted for publication in ApJ
Published: 2013
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45. Long-term TeV and X-ray Observations of the Gamma-ray Binary HESS J0632+057

Author: VERITAS Collaboration, Aliu, E., Archambault, S., Aune, T., Behera, B., Beilicke, M., Benbow, W., Berger, K., Bird, R., Bouvier, A., Buckley, J. H., Bugaev, V., Byrum, K., Cerruti, M., Chen, X., Ciupik, L., Connolly, M. P., Cui, W., Duke, C., Dumm, J., Errando, M., Falcone, A., Federici, S., Feng, Q., Finley, J. P., Fortin, P., Fortson, L., Furniss, A., Galante, N., Gillanders, G. H., Griffin, S., Griffiths, S. T., Grube, J., Gyuk, G., Hanna, D., Holder, J., Hughes, G., Humensky, T. B., Kaaret, P., Kertzman, M., Khassen, Y., Kieda, D., Krawczynski, H., Krennrich, F., Lang, M. J., Madhavan, A. S, Maier, G., Majumdar, P., McCann, A., Moriarty, P., Mukherjee, R., Nieto, D., de Bhróithe, A. O'Faoláin, Ong, R. A., Otte, A. N., Park, N., Perkins, J. S., Pohl, M., Popkow, A., Prokoph, H., Quinn, J., Ragan, K., Rajotte, J., Reyes, L. C., Reynolds, P. T., Richards, G. T., Roache, E., Rousselle, J., Sembroski, G. H., Sheidaei, F., Skole, C., Smith, A. W., Staszak, D., Stroh, M., Telezhinsky, I., Theiling, M., Tucci, J. V., Tyler, J., Varlotta, A., Vincent, S., Wakely, S. P., Weinstein, A., Welsing, R., Williams, D. A., Zajczyk, A., Zitzer, B., Collaboration, H. E. S. S., Abramowski, A., Aharonian, F., Benkhali, F. Ait, Akhperjanian, A. G., Angüner, E., Anton, G., Balenderan, S., Balzer, A., Barnacka, A., Becherini, Y., Tjus, J. Becker, Bernlöhr, K., Birsin, E., Bissaldi, E., Biteau, J., Böttcher, M., Boisson, C., Bolmont, J., Bordas, P., Brucker, J., Brun, F., Brun, P., Bulik, T., Carrigan, S., Casanova, S., Chadwick, P. M., Chalme-Calvet, R., Chaves, R. C. G., Cheesebrough, A., Chrétien, M., Colafrancesco, S., Cologna, G., Conrad, J., Couturier, C., Dalton, M., Daniel, M. K., Davids, I. D., Degrange, B., Deil, C., deWilt, P., Dickinson, H. J., Djannati-Ataï, A., Domainko, W., Drury, L. O'C., Dubus, G., Dutson, K., Dyks, J., Dyrda, M., Edwards, T., Egberts, K., Eger, P., Espigat, P., Farnier, C., Fegan, S., Feinstein, F., Fernandes, M. V., Fernandez, D., Fiasson, A., Fontaine, G., Forster, A., Füßling, M., Gajdus, M., Gallant, Y. A., Garrigoux, T., Giavitto, G., Giebels, B., Glicenstein, J. F., Grondin, M. -H., Grudzińska, M., Häffner, S., Hahn, J., Harris, J., Heinzelmann, G., Henri, G., Hermann, G., Hervet, O., Hillert, A., Hinton, J. A., Hofmann, W., Hofverberg, P., Holler, M., Horns, D., Jacholkowska, A., Jahn, C., Jamrozy, M., Janiak, M., Jankowsky, F., Jung, I., Kastendieck, M. A., Katarzyński, K., Katz, U., Kaufmann, S., Khélifi, B., Kieffer, M., Klepser, S., Klochkov, D., Kluźniak, W., Kneiske, T., Kolitzus, D., Komin, Nu., Kosack, K., Krakau, S., Krayzel, F., Krüger, P. P., Laffon, H., Lamanna, G., Lefaucheur, J., Lemiére, A., Lemoine-Goumard, M., Lenain, J. -P., Lennarz, D., Lohse, T., Lopatin, A., Lu, C. -C., Marandon, V., Marcowith, A., Marx, R., Maurin, G., Maxted, N., Mayer, M., McComb, T. J. L., Méhault, J., Menzler, U., Meyer, M., Moderski, R., Mohamed, M., Moulin, E., Murach, T., Naumann, C. L., de Naurois, M., Niemiec, J., Nolan, S. J., Oakes, L., Ohm, S., Wilhelmi, E. de Onña, Opitz, B., Ostrowski, M., Oya, I., Panter, M., Parsons, R. D., Arribas, M. Paz, Pekeur, N. W., Pelletier, G., Perez, J., Petrucci, P. -O., Peyaud, B., Pita, S., Poon, H., Pühlhofer, G., Punch, M., Quirrenbach, A., Raab, S., Raue, M., Reimer, A., Reimer, O., Renaud, M., Reyes, R. de los, Rieger, F., Rob, L., Romoli, C., Rosier-Lees, S., Rowell, G., Rudak, B., Rulten, C. B., Sahakian, V., Sanchez, D. A., Santangelo, A., Schlickeiser, R., Schüssler, F., Schulz, A., Schwanke, U., Schwarzburg, S., Schwemmer, S., Sol, H., Spengler, G., Spies, F., Stawarz, Ł., Steenkamp, R., Stegmann, C., Stinzing, F., Stycz, K., Sushch, I., Szostek, A., Tavernet, J. -P., Tavernier, T., Taylor, A. M., Terrier, R., Tluczykont, M., Trichard, C., Valerius, K., van Eldik, C., Vasileiadis, G., Venter, C., Viana, A., Vincent, P., Völk, H. J., Volpe, F., Vorster, M., Wagner, S. J., Wagner, P., Ward, M., Weidinger, M., Weitzel, Q., White, R., Wierzcholska, A., Willmann, P., Wörnlein, A., Wouters, D., Zacharias, M., Zdziarski, A. A., Zech, A., and Zechlin, H. -S.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: HESS J0632+057 is the only gamma-ray binary known so far whose position in the sky allows observations with ground-based observatories both in the northern and southern hemispheres. Here we report on long-term observations of HESS J0632+057 conducted with the VERITAS and H.E.S.S. Cherenkov Telescopes and the X-ray Satellite Swift, spanning a time range from 2004 to 2012 and covering most of the system's orbit. The VHE emission is found to be variable, and is correlated with that at X-ray energies. An orbital period of $315 ^{+6}_{-4}$ days is derived from the X-ray data set, which is compatible with previous results, $P = (321 \pm 5$) days. The VHE light curve shows a distinct maximum at orbital phases close to 0.3, or about 100 days after periastron passage, which coincides with the periodic enhancement of the X-ray emission. Furthermore, the analysis of the TeV data shows for the first time a statistically significant ($> 6.5 \sigma$) detection at orbital phases 0.6--0.9. The obtained gamma-ray and X-ray light curves and the correlation of the source emission at these two energy bands are discussed in the context of the recent ephemeris obtained for the system. Our results are compared to those reported for other gamma-ray binaries., Comment: 35 pages, 8 figures, accepted for publication in ApJ
Published: 2013
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46. VERITAS Observations of the Microquasar Cygnus X-3

Author: Archambault, S., Beilicke, M., Benbow, W., Berger, K., Bird, R., Bouvier, A., Buckley, J. H., Bugaev, V., Byrum, K., Cerruti, M., Chen, X., Ciupik, L., Connolly, M. P., Cui, W., Duke, C., Dumm, J., Errando, M., Falcone, A., Federici, S., Feng, Q., Finley, J. P., Fortson, L., Furniss, A., Galante, N., Gillanders, G. H., Griffin, S., Griffiths, S. T., Grube, J., Gyuk, G., Hanna, D., Holder, J., Hughes, G., Humensky, T. B., Kaaret, P., Kertzman, M., Khassen, Y., Kieda, D., Krawczynski, H., Lang, M. J., Madhavan, A. S, Maier, G., Majumdar, P., McArthur, S., McCann, A., Moriarty, P., Mukherjee, R., Nieto, D., de Bhróithe, A. O'Faoláin, Ong, R. A., Otte, A. N., Pandel, D., Park, N., Perkins, J. S., Pohl, M., Popkow, A., Prokoph, H., Quinn, J., Ragan, K., Rajotte, J., Reyes, L. C., Reynolds, P. T., Richards, G. T., Roache, E., Sembroski, G. H., Sheidaei, F., Smith, A. W., Staszak, D., Telezhinsky, I., Theiling, M., Tucci, J. V., Tyler, J., Varlotta, A., Vincent, S., Wakely, S. P., Weekes, T. C., Weinstein, A., Williams, D. A., Zitzer, B., and McCollough, M. L.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
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: Aliu, E., Archambault, S., Behera, B., Berger, K., Beilicke, M., Benbow, W., Bird, R., Bouvier, A., Bugaev, V., Cerruti, M., Chen, X., Ciupik, L., Connolly, M. P., Cui, W., Dumm, J., Falcone, A., Federici, S., Feng, Q., Finley, J. P., Fortin, P., Fortson, L., Furniss, A., Galante, N., Gillanders, G. H., Griffin, S., Griffiths, S. T., Grube, J., Gyuk, G., Hanna, D., Holder, J., Hughes, G., Humensky, T. B., Kaaret, P., Kertzman, M., Khassen, Y., Kieda, D., Krennrich, F., Lang, M. J., Maier, G., Majumdar, P., McArthur, S., McCann, A., Moriarty, P., Mukherjee, R., de Bhroithe, A. O'Faolain, Ong, R. A., Otte, A. N., Park, N., Perkins, J. S., Pohl, M., Popkow, A., Prokoph, H., Quinn, J., Ragan, K., Rajotte, J., Ratliff, G., Reynolds, P. T., Richards, G. T., Roache, E., Sembroski, G. H., Sheidaei, F., Skole, C., Smith, A. W., Staszak, D., Telezhinsky, I., Tyler, J., Varlotta, A., Vincent, S., Wakely, S. P., Weekes, T. C., Weinstein, A., Welsing, R., Zajczyk, A., and Zitzer, B.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
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., Comment: Accepted for Publication in ApJ
Published: 2013
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48. Long term observations of B2 1215+30 with VERITAS

Author: VERITAS collaboration, Aliu, E., Archambault, S., Arlen, T., Aune, T., Beilicke, M., Benbow, W., Bird, R., Bouvier, A., Buckley, J. H., Bugaev, V., Cesarini, A., Ciupik, L., Connolly, M. P., Cui, W., Dumm, J., Errando, M., Falcone, A., Federici, S., Feng, Q., Finley, J. P., Fortin, P., Fortson, L., Furniss, A., Galante, N., Gérard, L., Gillanders, G. H., Griffin, S., Grube, J., Gyuk, G., Hanna, D., Holder, J., Hughes, G., Humensky, T. B., Kaaret, P., Kertzman, M., Khassen, Y., Kieda, D., Krawczynski, H., Krennrich, F., Lang, M. J., Madhavan, A. S, Maier, G., Majumdar, P., McArthur, S., McCann, A., Moriarty, P., Mukherjee, R., Nieto, D., de Bhróithe, A. O'Faoláin, Ong, R. A., Orr, M., Otte, A. N., Park, N., Perkins, J. S., Pohl, M., Popkow, A., Prokoph, H., Quinn, J., Ragan, K., Reyes, L. C., Reynolds, P. T., Richards, G. T., Roache, E., Saxon, D. B., Sembroski, G. H., Skole, C., Smith, A. W., Soares-Furtado, M., Staszak, D., Telezhinsky, I., Tešić, G., Theiling, M., Varlotta, A., Vassiliev, V. V., Vincent, S., Wakely, S. P., Weekes, T. C., Weinstein, A., Welsing, R., Williams, D. A., Zitzer, B., Böttcher, M., Fumagalli, M., and Jadhav, J.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: We report on VERITAS observations of the BL Lac object B2 1215+30 between 2008 and 2012. During this period, the source was detected at very high energies (VHE; E > 100 GeV) by VERITAS with a significance of $8.9\sigma$ and showed clear variability on time scales larger than months. In 2011, the source was found to be in a relatively bright state and a power-law fit to the differential photon spectrum yields a spectral index of $3.6 \pm 0.4_{\mathrm{stat}} \pm 0.3_{\mathrm{syst}}$ with an integral flux above 200 GeV of $(8.0 \pm 0.9_{\mathrm{stat}} \pm 3.2_{\mathrm{syst}}) \times 10^{-12}\, \mathrm{cm}^{-2} \mathrm{s}^{-1}$. No short term variability could be detected during the bright state in 2011. Multi-wavelength data were obtained contemporaneous with the VERITAS observations in 2011 and cover optical (Super-LOTIS, MDM, Swift-UVOT), X-ray (Swift-XRT), and gamma-ray (Fermi-LAT) frequencies. These were used to construct the spectral energy distribution (SED) of B2 1215+30. A one-zone leptonic model is used to model the blazar emission and the results are compared to those of MAGIC from early 2011 and other VERITAS-detected blazars. The SED can be well reproduced with model parameters typical for VHE-detected BL Lacs., Comment: 34 pages, 5 figures, accepted for publication in ApJ
Published: 2013
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49. A search for enhanced very high energy gamma-ray emission from the March 2013 Crab Nebula flare

Author: The VERITAS Collaboration, Aliu, E., Archambault, S., Aune, T., Benbow, W., Berger, K., Bird, R., Bouvier, A., Buckley, J. H., Bugaev, V., Byrum, K., Cerruti, M., Chen, X., Ciupik, L., Connolly, M. P., Cui, W., Dumm, J., Errando, M., Falcone, A., Federici, S., Feng, Q., Finley, J. P., Fortin, P., Fortson, L., Furniss, A., Galante, N., Gillanders, G. H., Griffin, S., Griffiths, S. T., Grube, J., Gyuk, G., Hanna, D., Holder, J., Hughes, G., Humensky, T. B., Kaaret, P., Kertzman, M., Khassen, Y., Kieda, D., Krennrich, F., Kumar, S., Lang, M. J., Lyutikov, M., Maier, G., McArthur, S., McCann, A., Meagher, K., Millis, J., Moriarty, P., Mukherjee, R., de Bhroithe, A. O'Faolain, Ong, R. A., Otte, A. N., Perkins, J. S., Pohl, M., Popkow, A., Quinn, J., Ragan, K., Rajotte, J., Reyes, L. C., Reynolds, P. T., Richards, G. T., Roache, E., Sembroski, G. H., Sheidaei, F., Smith, A. W., Staszak, D., Telezhinsky, I., Theiling, M., Tucci, J. V., Tyler, J., Varlotta, A., Wakely, S. P., Weekes, T. C., Weinstein, A., Welsing, R., Williams, D. A., Zajczyk, A., and Zitzer, B.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: In March 2013, a flaring episode from the Crab Nebula lasting ~2 weeks was detected by the Fermi-LAT (Large Area Telescope on board the Fermi Gamma-ray Space Telescope). VERITAS provides simultaneous observations throughout this period. During the flare, the Fermi-LAT detected a 20-fold increase in flux above the average synchrotron flux >100 MeV seen from the Crab Nebula. Simultaneous measurements with VERITAS are consistent with the non-variable long-term average Crab Nebula flux at TeV energies. Assuming a linear correlation between the very-high-energy flux change >1 TeV and the flux change seen in the Fermi-LAT band >100 MeV during the period of simultaneous observations, the linear correlation factor can be constrained to be at most 8.6 * 10^-3 with 95% confidence., Comment: 4 figures, 1 table, published in The Astrophysical Journal Letters
Published: 2013
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50. VERITAS contributions to the 33rd International Cosmic Ray Conference

Author: VERITAS Collaboration, Aliu, E., Archambault, S., Aune, T., Behera, B., Beilicke, M., Benbow, W., Berger, K., Bird, R., Bouvier, A., Buckley, J. H., Bugaev, V., Byrum, K., Cardenzana, J. V, Cerruti, M., Ciupik, L., Connolly, M. P., Cui, W., Dumm, J., Dwarkadas, V. V., Errando, M., Falcone, A., Federici, S., Feng, Q., Finley, J. P., Fortin, P., Fortson, L., Furniss, A., Galante, N., Gillanders, G. H., Griffin, S., Griffiths, S. T., Grube, J., Gyuk, G., Hanna, D., Holder, J., Hughes, G., Humensky, T. B., Kaaret, P., Kertzman, M., Khassen, Y., Kieda, D., Krawczynski, H., Krennrich, F., Kumar, S., Lang, M. J., Madhavan, A. S, Maier, G., Majumdar, P., McArthur, S., McCann, A., Millis, J., Moriarty, P., Mukherjee, R., Nelson, T., Nieto, D., O'Faolain, A. de Bhroithe, Ong, R. A., Otte, A. N., Park, N., Perkins, J. S., Pohl, M., Popkow, A., Prokoph, H., Quinn, J., Ragan, K., Rajotte, J., Reyes, L. C., Reynolds, P. T., Richards, G. T., Roache, E., Rousselle, J., Sembroski, G. H., Sheidaei, F., Smith, A. W., Staszak, D., Telezhinsky, I., Theiling, M., Tucci, J. V., Tyler, J., Varlotta, A., Vincent, S., Wagner, R. G., Wakely, S. P., Weekes, T. C., Weinstein, A., Welsing, R., Williams, D. A., and Zitzer, B.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: Compilation of papers contributed by the VERITAS Collaboration to the 33rd International Cosmic Ray Conference, held 2-9 July, 2013, in Rio de Janeiro, Brazil.
Published: 2013

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