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1. Rapid X-ray Variability in Mkn 421 during a Multiwavelength Campaign

Author

Markowitz, Alex G., Nalewajko, Krzysztof, Bhatta, Gopal, Dewangan, Gulab C., Chandra, Sunil, Dorner, Daniela, Schleicher, Bernd, Pajdosz-Smierciak, Urszula, Stawarz, Lukasz, Zola, Staszek, Ostrowski, Michal, Carosati, Daniele, Krishnan, Saikruba, Bachev, Rumen, Benitez, Erika, Gazeas, Kosmas, Hiriart, David, Hu, Shao-Ming, Larionov, Valeri, Marchini, Alessandro, Matsumoto, Katsura, Nikiforova, A. A., Pursimo, Tapio, Raiteri, Claudia M., Reichart, Daniel E., Rodriguez, Diego, Semkov, Evgeni, Strigachev, Anton, Sugiura, Yuki, Villata, Massimo, Webb, James R., Arbet-Engels, Axel, Baack, Dominik, Balbo, Matteo, Biland, Adrian, Bretz, Thomas, Buss, Jens, Eisenberger, Laura, Elsaesser, Dominik, Hildebrand, Dorothee, Iotov, Roman, Kalenski, Adelina, Mannheim, Karl, Mitchell, Alison, Neise, Dominik, Noethe, Maximilian, Paravac, Aleksander, Rhode, Wolfgang, Sliusar, Vitalii, and Walter, Roland

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract

The study of short-term variability properties in AGN jets has the potential to shed light on their particle acceleration and emission mechanisms. We report results from a four-day coordinated multi-wavelength campaign on the highly-peaked blazar (HBL) Mkn 421 in 2019 January. We obtained X-ray data from AstroSAT, BVRI photometry with the Whole Earth Blazar Telescope (WEBT), and TeV data from FACT to explore short-term multi-wavelength variability in this HBL. The X-ray continuum is rapidly variable on time-scales of tens of ks. Fractional variability amplitude increases with energy across the synchrotron hump, consistent with previous studies; we interpret this observation in the context of a model with multiple cells whose emission spectra contain cutoffs that follow a power-law distribution. We also performed time-averaged and time-resolved (time-scales of 6 ks) spectral fits; a broken power-law model fits all spectra well; time-resolved spectral fitting reveals the usual hardening when brightening behaviour. Intra-X-ray cross correlations yield evidence for the 0.6-0.8 keV band to likely lead the other bands by an average of 4.6 +- 2.6 ks, but only during the first half of the observation. The source displayed minimal night-to-night variability at all wavebands thus precluding significant interband correlations during our campaign. The broadband SED is modeled well with a standard one-zone leptonic model, yielding jet parameters consistent with those obtained from previous SEDs of this source., Comment: This article has been accepted for publication in The Monthly Notices of the Royal Astronomical Society (2022), and is published in Volume 513, Issue 2, pp.1662-1679. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. 19 pages; 12 figures

Published
2022
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2. Statistical properties of flux variations in blazar light curves at GeV and TeV energies

Author

Wagner, Sarah M., Burd, Paul R., Dorner, Daniela, Mannheim, Karl, Buson, Sara, Gokus, Andrea, Madejski, Greg, Scargle, Jeffrey D., Arbet-Engels, Axel, Baack, Dominik, Balbo, Matteo, Biland, Adrian, Bretz, Thomas, Buss, Jens, Eisenberger, Laura, Elsaesser, Dominik, Hildebrand, Dorothee, Iotov, Roman, Kalenski, Adelina, Neise, Dominik, Noethe, Maximilian, Paravac, Aleksander, Rhode, Wolfgang, Schleicher, Bernd, Sliusar, Vitalii, and Walter, Roland

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

Despite numerous detections of individual flares, the physical origin of the rapid variability observed from blazars remains uncertain. Using Bayesian blocks and the Eisenstein-Hut HOP algorithm, we characterize flux variations of high significance in the $\gamma$-ray light curves of two samples of blazars. Daily binned long-term light curves of TeV-bright blazars observed with the First G-APD Cherenkov Telescope (FACT) are compared to those of GeV-bright blazars observed with the Large Area Telescope on board the $Fermi$ Gamma-ray Space Telescope ($Fermi$-LAT). We find no evidence for systematic asymmetry of the flux variations based on the derived rise and decay time scales. Additionally, we show that the daily-binned blazar light curves can be described by an exponential stochastic Ornstein-Uhlenbeck (OU) process with parameters depending on energy. Our analysis suggests that the flux variability in both samples is a superposition of faster fluctuations. This is, for instance, challenging to explain by shock-acceleration but expected for magnetic reconnection., Comment: for associated HOP algorithm, see https://github.com/swagner-astro/lightcurves and for associated OU algorithm, see https://github.com/PRBurd/astro-wue

Published
2021
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3. Long-term multi-band photometric monitoring of Mrk 501

Author

Arbet-Engels, Axel, Baack, Dominik, Balbo, Matteo, Biland, Adrian, Bretz, Thomas, Buss, Jens, Dorner, Daniela, Eisenberger, Laura, Elsaesser, Dominik, Hildebrand, Dorothee, Iotov, Roman, Kalenski, Adelina, Mannheim, Karl, Mitchell, Alison, Neise, Dominik, Noethe, Maximilian, Paravac, Aleksander, Rhode, Wolfgang, Schleicher, Bernd, Sliusar, Vitalii, and Walter, Roland

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract

Radio-to-TeV observations of the bright nearby (z=0.034) blazar Markarian 501 (Mrk 501), performed from December 2012 to April 2018, are used to study the emission mechanisms in its relativistic jet. We examined the multi-wavelength variability and the correlations of the light curves obtained by eight different instruments, including the First G-APD Cherenkov Telescope (FACT), observing Mrk 501 in very high-energy (VHE) gamma-rays at TeV energies. We identified individual TeV and X-ray flares and found a sub-day lag between variability in these two bands. Simultaneous TeV and X-ray variations with almost zero lag are consistent with synchrotron self-Compton (SSC) emission, where TeV photons are produced through inverse Compton scattering. The characteristic time interval of 5-25 days between TeV flares is consistent with them being driven by Lense-Thirring precession., Comment: 10 pages, 11 figures, Astronomy and astrophysics pre-print. arXiv admin note: text overlap with arXiv:2101.10651

Published
2021
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4. Relentless multi-wavelength variability of Mrk 421 and Mrk 501

Author

Sliusar, Vitalii, Arbet-Engels, Axel, Baack, Dominik, Balbo, Matteo, Biland, Adrian, Bretz, Thomas, Buss, Jens, Dorner, Daniela, Eisenberger, Laura, Elsaesser, Dominik, Hildebrand, Dorothee, Iotov, Roman, Kalenski, Adelina, Mannheim, Karl, Mitchell, Alison, Neise, Dominik, Noethe, Maximilian, Paravac, Aleksander, Rhode, Wolfgang, Schleicher, Bernd, and Walter, Roland

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract

Mrk 421 and Mrk 501 are two close, bright and well-studied high-synchrotron-peaked blazars, which feature bright and persistent GeV and TeV emission. We use the longest and densest dataset of unbiased observations of these two sources, obtained at TeV and GeV energies during five years with FACT and Fermi-LAT. To characterize the variability and derive constraints on the emission mechanism, we augment the dataset with contemporaneous multi-wavelength observations from radio to X-rays. We correlate the light curves, identify individual flares in TeV energies and X-rays, and look for inter-band connections, which are expected from the shock propagations within the jet. For Mrk 421, we find that the X-rays and TeV energies are well correlated with close to zero lag, supporting the SSC emission scenario. The timing between the TeV, X-ray flares in Mrk 421 is consistent with periods expected in the case of Lense-Thirring precession of the accretion disc. The variability of Mrk 501 on long-term periods is also consistent with SSC, with a sub-day lag between X-rays and TeV energies. Fractional variability for both blazars shows a two bump structure with the highest variability in the X-ray and TeV bands., Comment: 8 pages, 3 figures

Published
2021
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5. 5.5 years multi-wavelength variability of Mrk 421: evidences of leptonic emission from the radio to TeV

Author

Sliusar, Vitalii, Arbet-Engels, Axel, Baack, Dominik, Balbo, Matteo, Beck, Marvin, Biland, Adrian, Blank, Michael, Bretz, Thomas, Bruegge, Kai, Bulinski, Michael, Buss, Jens, Doerr, Manuel, Dorner, Daniela, Elsaesser, Dominik, Hildebrand, Dorothee, Iotov, Roman, Klinger, Marc, Mannheim, Karl, Neise, Dominik, Noethe, Maximilian, Paravac, Aleksander, Rhode, Wolfgang, Schleicher, Bernd, Sedlaczek, Kevin, Shukla, Amit, Tani, Laurits, Theissen, Fabian, and Walter, Roland

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract

Mrk 421 is a high-synchrotron-peaked blazar featuring bright and persistent GeV and TeV emission. We use the longest and densest ongoing unbiased observing campaign obtained at TeV and GeV energies during 5.5 years with the FACT telescope and the Fermi-LAT detector. The contemporaneous multi-wavelength observations were used to characterize the variability of the source and to constrain the underlying physical mechanisms. We study and correlate light curves obtained by nine different instruments from radio to gamma rays and found two significant results. The TeV and X-ray light curves are very well correlated with lag, if any, shorter than a day. The GeV light curve varies independently and accurately leads the variations observed at long wavelengths, in particular in the radio band. We find that the observations match the predictions of leptonic models and suggest that the physical conditions vary along the jet, when the emitting region moves outwards., Comment: 7 pages, 2 figures, 1 table. High Energy Phenomena in Relativistic Outflows VII (HEPRO VII), 9-12 July, 2019. Barcelona, Spain

Published
2019

6. Rapid X-ray variability in Mkn 421 during a multiwavelength campaign

Author

Markowitz, Alex G, primary, Nalewajko, Krzysztof, additional, Bhatta, Gopal, additional, Dewangan, Gulab C, additional, Chandra, Sunil, additional, Dorner, Daniela, additional, Schleicher, Bernd, additional, Pajdosz-Śmierciak, Urszula, additional, Stawarz, Łukasz, additional, Zola, Staszek, additional, Ostrowski, Michał, additional, Carosati, Daniele, additional, Krishnan, Saikruba, additional, Bachev, Rumen, additional, Benítez, Erika, additional, Gazeas, Kosmas, additional, Hiriart, David, additional, Hu, Shao-Ming, additional, Larionov, Valeri, additional, Marchini, Alessandro, additional, Matsumoto, Katsura, additional, Nikiforova, A A, additional, Pursimo, Tapio, additional, Raiteri, Claudia M, additional, Reichart, Daniel E, additional, Rodriguez, Diego, additional, Semkov, Evgeni, additional, Strigachev, Anton, additional, Sugiura, Yuki, additional, Villata, Massimo, additional, Webb, James R, additional, Arbet-Engels, Axel, additional, Baack, Dominik, additional, Balbo, Matteo, additional, Biland, Adrian, additional, Bretz, Thomas, additional, Buss, Jens, additional, Eisenberger, Laura, additional, Elsaesser, Dominik, additional, Hildebrand, Dorothee, additional, Iotov, Roman, additional, Kalenski, Adelina, additional, Mannheim, Karl, additional, Mitchell, Alison, additional, Neise, Dominik, additional, Noethe, Maximilian, additional, Paravac, Aleksander, additional, Rhode, Wolfgang, additional, Sliusar, Vitalii, additional, and Walter, Roland, additional

Published
2022
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7. Relentless multi-wavelength variability of Mrk 421 and Mrk 501

Author

Sliusar, Vitalii, Arbet-Engels, Axel, Baack, Dominik, Balbo, Matteo, Biland, Adrian, Bretz, Thomas, Buss, Jens, Dorner, Daniela, Eisenberger, Laura, Elsaesser, Dominik, Hildebrand, Dorothée, Iotov, Roman, Kalenski, Adelina, Mannheim, Karl, Mitchell, Alison, Neise, Dominik, Noethe, Maximilian, Paravac, Aleksander, Rhode, Wolfgang, Schleicher, Bernd, and Walter, Roland

Subjects
Tellurium compounds, Shock propagation, Blazars, Emission mechanism, Emission scenarios, Energy, Lense-thirring, light curves, Multiwavelengths, Two sources, X ray flares, Germanium compounds
Abstract

Mrk 421 and Mrk 501 are two close, bright and well-studied high-synchrotron-peaked blazars, which feature bright and persistent GeV and TeV emission. We use the longest and densest dataset of unbiased observations of these two sources, obtained at TeV and GeV energies during five years with FACT and Fermi-LAT. To characterize the variability and derive constraints on the emission mechanism, we augment the dataset with contemporaneous multi-wavelength observations from radio to X-rays. We correlate the light curves, identify individual flares in TeV energies and X-rays, and look for inter-band connections, which are expected from the shock propagations within the jet. For Mrk 421, we find that the X-rays and TeV energies are well correlated with close to zero lag, supporting the SSC emission scenario. The timing between the TeV, X-ray flares in Mrk 421 is consistent with periods expected in the case of Lense-Thirring precession of the accretion disc. The variability of Mrk 501 on long-term periods is also consistent with SSC, with a sub-day lag between X-rays and TeV energies. Fractional variability for both blazars shows a two bump structure with the highest variability in the X-ray and TeV bands., PoS: Proceedings of Science, 395, ISSN:1824-8039, Proceedings of 37th International Cosmic Ray Conference

Published
2022

8. Relentless multi-wavelength variability of Markarian 421 and Markarian 501

Author

FACT Collaboration, Sliusar, Vitalii, Arbet Engels, Axel, Baack, Dominik, Balbo, Matteo, Biland, Adrian, Bretz, Thomas, Buss, Jens, Dorner, Daniela, Eisenberger, Laura, Elsaesser, Dominik, Hildebrand, Dorothée, Iotov, Roman, Kalenski, Adelina, Mannheim, Karl, Mitchell, Alison, Neise, Dominik, Noethe, Maximilian, Paravac, Aleksander, Rhode, Wolfgang, Schleicher, Bernd, and Walter, Roland

Subjects
Physics, Accretion disc, Astrophysics::High Energy Astrophysical Phenomena, Precession, Multi wavelength, High Energy Physics::Experiment, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Light curve, Blazar, Astrophysics::Galaxy Astrophysics
Abstract

Mrk 421 and Mrk 501 are two close bright and well-studied high-synchrotron-peaked blazars, which feature bright and persistent GeV and TeV emission. We use the longest and densest dataset of unbiased observations of these two sources, obtained at TeV and GeV energies during 5 years with the FACT telescope and Fermi-LAT. To characterize the variability and derive constraints on the emission mechanism, we augment the dataset with contemporaneous multi-wavelength observations from radio to X-rays. We correlate the light curves, identify individual flares in TeV and X-rays, and look for inter-band connections, which are expected from the shock propagations within the jet. For Mrk 421 we find that the X-rays and TeV are well correlated with close to zero lag, supporting the SSC emission scenario. The timing between the TeV, X-ray flares in Mrk 421 is consistent with periods expected in the case of Lense–Thirring precession of the accretion disc. Mrk 501 variability on long-term periods is also consistent with SSC, with a sub-day lag between X-rays and TeVs. Fractional variability for both blazars shows two bump structure with the highest variability in X-ray and TeV bands., PoS: Proceedings of Science, 395, ISSN:1824-8039, 37th International Cosmic Ray Conference (ICRC 2021)

Published
2022

9. Multi-wavelength study of Mrk 421 during a TeV flare

Author

Gokus, Andrea, Kreikenbohm, Annika, Leiter, Katharina, Bretz, Thomas, Dauser, Thomas, Dorner, Daniela, Elsaesser, Dominik, Eppel, Florian, Heßdörfer, Jonas, Kadler, Matthias, Kraus, Alexander, Kreter, Michael, Kreykenbohm, Ingo, Langejahn, Marcus, Mannheim, Karl, Thalhammer, Philipp, Wilms, Joern, FACT Collaboration, Arbet Engels, Axel, Baack, Dominik, Balbo, Matteo, Biland, Adrian, Buss, Jens, Eisenberger, Laura, Hildebrand, Dorothée, Iotov, Roman, Kalenski, Adelina, Mitchell, Alison, Neise, Dominik, Noethe, Maximilian, Paravac, Aleksander, Rhode, Wolfgang, Schleicher, Bernd, Sliusar, Vitalii, and Walter, Roland

Subjects
Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Cosmology and Extragalactic Astrophysics
Abstract

The blazar Mrk 421 shows frequent, short flares in the TeV energy regime. Due to the fast nature of such episodes, we often fail to obtain sufficient simultaneous information about flux variations in several energy bands. To overcome this lack of multi-wavelength (MWL) coverage, especially for the pre- and post-flare periods, we have set up a monitoring program with the FACT telescope (TeV energies) and the Neil Gehrels Swift Observatory (X-rays). On 2019 June 9, Mrk 421 showed a TeV outburst reaching a flux level of more than two times the flux of the Crab Nebula at TeV energies. We acquired simultaneous data in the X-rays with additional observations by XMM-Newton and INTEGRAL. For the first time, we can study a TeV blazar in outburst taking advantage of highly sensitive X-ray data from XMM-Newton and INTEGRAL combined. Our data set is complemented by pointed radio observations by Effelsberg at GHz frequencies. We present our first results, including the gamma-ray and X-ray light curves, a timing analysis of the X-ray data obtained with XMM-Newton, as well as the radio spectra before, during and after the flare., PoS: Proceedings of Science, 395, ISSN:1824-8039, 37th International Cosmic Ray Conference (ICRC 2021)

Published
2022

10. Statistical properties of flux variations in blazar light curves at GeV and TeV energies

Author

Fermi-LAT Collaboration, Wagner, Sarah M., Burd, Paul, Dorner, Daniela, Mannheim, Karl, Buson, Sara, Gokus, Andrea, Madejski, Greg, Scargle, Jeffrey D., FACT Collaboration, Arbet Engels, Axel, Baack, Dominik, Balbo, Matteo, Biland, Adrian, Bretz, Thomas, Buss, Jens, Elsaesser, Dominik, Eisenberger, Laura, Hildebrand, Dorothée, Iotov, Roman, Kalenski, Adelina, Neise, Dominik, Noethe, Maximilian, Paravac, Aleksander, Rhode, Wolfgang, Schleicher, Bernd, Sliusar, Vitalii, and Walter, Roland

Subjects
Physics, High Energy Astrophysical Phenomena (astro-ph.HE), media_common.quotation_subject, Astrophysics::High Energy Astrophysical Phenomena, Flux, FOS: Physical sciences, Magnetic reconnection, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Light curve, Asymmetry, law.invention, Telescope, Spitzer Space Telescope, law, Blazar, Astrophysics - High Energy Astrophysical Phenomena, Cherenkov radiation, media_common
Abstract

Despite numerous detections of individual flares, the physical origin of the rapid variability observed from blazars remains uncertain. Using Bayesian blocks and the Eisenstein-Hut HOP algorithm, we characterize flux variations of high significance in the γ-ray light curves of two samples of blazars. Daily binned long-term light curves of TeV-bright blazars observed with the First G-APD Cherenkov Telescope (FACT) are compared to those of GeV-bright blazars observed with the Large Area Telescope on board the Fermi Gamma-ray Space Telescope (Fermi-LAT). We find no evidence for systematic asymmetry of the flux variations based on the derived rise and decay time scales. Additionally, we show that the daily-binned blazar light curves can be described by an exponential stochastic Ornstein-Uhlenbeck process with parameters depending on energy. Our analysis suggests that the flux variability in both samples is a superposition of faster fluctuations. This is, for instance, challenging to explain by shock-acceleration but expected for magnetic reconnection., PoS: Proceedings of Science, 395, ISSN:1824-8039, 37th International Cosmic Ray Conference (ICRC 2021)

Published
2021

11. FACT - Multi-wavelength analysis of more than 30 flares of Mrk 421

Author

Sliusar, Vitalii, Arbet Engels, Axel, Baack, Dominik, Balbo, Matteo, Beck, Marvin, Biland, Adrian, Blank, Michael, Bretz, Tomas, Bruegge, Kai, Bulinski, Michael, Buss, Jens, Doerr, Manuel, Dorner, Daniela, Elsaesser, Dominik, Hildebrand, Dorothée, Iotov, Roman, Klinger, Marc, Mannheim, Karl, Mueller, Sebastian, Neise, Dominik, Noethe, Maximilian, Paravac, Aleksander, Rhode, Wolfgang, Schleicher, Bernd, Sedlaczek, Kevin, Shukla, Amit, Tani, Laurits, Theissen, Fabian, Walter, Roland, and von Willert, Elan

Subjects
Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Astrophysics::High Energy Astrophysical Phenomena, Gamma ray, Flux, FOS: Physical sciences, Electron, Astrophysics, Light curve, law.invention, Amplitude, law, High Energy Physics::Experiment, Blazar, Astrophysics - High Energy Astrophysical Phenomena, Flare, Fermi Gamma-ray Space Telescope
Abstract

Mrk 421 is a high-synchrotron-peaked blazar featuring bright and persistent GeV and TeV emission. We use multi-wavelength light curves of Mrk 421 spanning 5.5 years with FACT (TeV) and Fermi LAT (GeV) in the gamma rays, Swift BAT, Swift XRT and MAXI in the X-rays, together with optical and radio data and investigate the physical processes driving the emission and variability. Observations by FACT are continuous and not triggered, so the source was found in a wide range of flux states and more than 30 flares were identified from X-rays to TeV. The light curves in TeV and X-rays feature very similar flares with rise and decay times of a few days and zero lag, characteristic for electron processes. At least two parameters per flare, the amplitude and the cut-off energy, are required to explain the observed variability. In addition, the GeV light curve leads and is strongly correlated with the optical and radio light curves as expected from SSC emitting shock propagating in a conical jet., PoS: Proceedings of Science, 358, ISSN:1824-8039, Proceedings of th 36th International Cosmic Ray Conference (ICRC 2019)

Published
2021

12. Long-term multi-band photometric monitoring of Mrk 501

Author

Arbet-Engels, Axel, primary, Baack, Dominik, additional, Balbo, Matteo, additional, Biland, Adrian, additional, Bretz, Thomas, additional, Buss, Jens, additional, Dorner, Daniela, additional, Eisenberger, Laura, additional, Elsaesser, Dominik, additional, Hildebrand, Dorothee, additional, Iotov, Roman, additional, Kalenski, Adelina, additional, Mannheim, Karl, additional, Mitchell, Alison, additional, Neise, Dominik, additional, Noethe, Maximilian, additional, Paravac, Aleksander, additional, Rhode, Wolfgang, additional, Schleicher, Bernd, additional, Sliusar, Vitalii, additional, and Walter, Roland, additional

Published
2021
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13. Multiwavelength variability and correlation studies of Mrk421 during historically low X-ray and γ-ray activity in 2015–2016

Author

Banerjee, Biswajit, primary, Acciari, Victor A., additional, Ansoldi, Stefano, additional, Antonelli, Lucio Angelo, additional, Arbet Engels, Axel, additional, Artero, Manuel, additional, Asano, Katsuaki, additional, Baack, Dominik, additional, Babić, Ana, additional, Baquero, Andrés, additional, Barres de Almeida, Ulisses, additional, Barrio, Juan Abel, additional, Batković, Ivana, additional, Becerra González, Josefa, additional, Bednarek, Wlodek, additional, Bellizzi, Lorenzo, additional, Bernardini, Elisa, additional, Bernardos, Maria-Isabel, additional, Berti, Alessio, additional, Besenrieder, Jürgen, additional, Bhattacharyya, Wrijupan, additional, Bigongiari, Ciro, additional, Biland, Adrian, additional, Blanch, Oscar, additional, Bökenkamp, Hendrik, additional, Bonnoli, Giacomo, additional, Bošnjak, Željka, additional, Busetto, Giovanni, additional, Carosi, Roberto, additional, Ceribella, Giovanni, additional, Cerruti, Matteo, additional, Chai, Yating, additional, Chilingarian, Ashot Agassi, additional, Cikota, Stefan, additional, Colak, Sidika Merve, additional, Colombo, Eduardo, additional, Contreras, Jose Luis, additional, Cortina, Juan, additional, Covino, Stefano, additional, D'Amico, Giacomo, additional, D'Elia, Valerio, additional, Da Vela, Paolo, additional, Dazzi, Francesco, additional, De Angelis, Alessandro, additional, De Lotto, Barbara, additional, Delfino, Manuel, additional, Delgado, Jordi, additional, Delgado Mendez, Carlos, additional, Depaoli, Davide, additional, Di Pierro, Federico, additional, Di Venere, Leonardo, additional, Do Souto Espiñeira, Elia, additional, Dominis Prester, Dijana, additional, Donini, Alice, additional, Dorner, Daniela, additional, Doro, Michele, additional, Elsaesser, Dominik, additional, Fallah Ramazani, Vandad, additional, Fattorini, Alicia, additional, Fonseca, Maria Victoria, additional, Font, Lluis, additional, Fruck, Christian, additional, Fukami, Satoshi, additional, Fukazawa, Yasushi, additional, García López, Ramon J., additional, Garczarczyk, Markus, additional, Gasparyan, Sargis, additional, Gaug, Markus, additional, Giglietto, Nicola, additional, Giordano, Francesco, additional, Gliwny, Pawel, additional, Godinović, Nikola, additional, Green, David, additional, Green, Jarred Gershon, additional, Hadasch, Daniela, additional, Hahn, Alexander, additional, Heckmann, Lea, additional, Herrera, Javier, additional, Hoang, John, additional, Hrupec, Dario, additional, Hütten, Moritz, additional, Inada, Tomohiro, additional, Ishio, Kazuma, additional, Iwamura, Yuki, additional, Jimenez-Martinez, Irene, additional, Jormanainen, Jenni, additional, Jouvin, Léa, additional, Karjalainen, Marie, additional, Kerszberg, Daniel, additional, Kobayashi, Yukiho, additional, Kubo, Hidetoshi, additional, Kushida, Junko, additional, Lamastra, Alessandra, additional, LELAS, Damir, additional, Leone, Francesco, additional, Lindfors, Elina, additional, Linhoff, Lena, additional, Lombardi, Saverio, additional, Longo, Francesco, additional, López-Coto, Rubén, additional, López-Moya, Marcos, additional, López-Oramas, Alicia, additional, Loporchio, Serena, additional, Machado de Oliveira Fraga, Bernardo, additional, Maggio, Camilla, additional, Majumdar, Pratik, additional, MAKARIEV, Martin, additional, Mallamaci, Manuela, additional, Maneva, Galina, additional, Manganaro, Marina, additional, Mannheim, Karl, additional, Maraschi, Laura, additional, Mariotti, Mosè, additional, Martínez, Manel, additional, Mazin, Daniel, additional, Menchiari, Stefano, additional, Mender, Simone, additional, Mićanović, Saša, additional, Miceli, Davide, additional, Miener, Tjark, additional, Miranda, Jose Miguel, additional, Mirzoyan, Razmik, additional, Molina, Edgar, additional, Moralejo, Abelardo, additional, Morcuende, Daniel, additional, Moreno, Victoria, additional, Moretti, Elena, additional, Nakamori, Takeshi, additional, Nava, Lara, additional, Neustroev, Vitaly, additional, Nigro, Cosimo, additional, Nilsson, Kari, additional, Nishijima, Kyoshi, additional, Noda, Koji, additional, Nozaki, Seiya, additional, Ohtani, Yoshiki, additional, Oka, Tomohiko, additional, Otero-Santos, Jorge, additional, Paiano, Simona, additional, Palatiello, Michele, additional, Paneque, David, additional, Paoletti, Riccardo, additional, Paredes, Josep M., additional, Pavletić, Lovro, additional, Peñil, Pablo, additional, Persic, Massimo, additional, Pihet, Marine, additional, Prada Moroni, Pier Giorgio, additional, Prandini, Elisa, additional, Priyadarshi, Chaitanya, additional, Puljak, Ivica, additional, Rhode, Wolfgang, additional, Ribó, Marc, additional, Rico, Javier, additional, Righi, Chiara, additional, Rugliancich, Andrea, additional, Sahakyan, Narek, additional, Saito, Takayuki, additional, Sakurai, Shunsuke, additional, Satalecka, Konstancja, additional, Saturni, Francesco Gabriele, additional, Schleicher, Bernd, additional, Schmidt, Kevin, additional, Schweizer, Thomas, additional, Sitarek, Julian, additional, Šnidarić, Iva, additional, Sobczyńska, Dorota, additional, Spolon, Alessia, additional, Stamerra, Antonio, additional, Strišković, Jelena, additional, Strom, Derek, additional, Strzys, Marcel C., additional, Suda, Yusuke, additional, Surić, Tihomir, additional, Takahashi, Mitsunari, additional, Takeishi, Ryuji, additional, Tavecchio, Fabrizio, additional, Temnikov, Petar, additional, Terzić, Tomislav, additional, Teshima, Masahiro, additional, Tosti, Luca, additional, Truzzi, Stefano, additional, Tutone, Antonio, additional, Ubach, Santiago, additional, van Scherpenberg, Juliane, additional, Vanzo, Gaia, additional, VAZQUEZ ACOSTA, Monica, additional, Ventura, Sofia, additional, VERGUILOV, Vassil, additional, Vigorito, Carlo francesco, additional, Vitale, Vincenzo, additional, Vovk, Ievgen, additional, Will, Martin, additional, Wunderlich, Carolin, additional, Yamamoto, Tokonatsu, additional, Zarić, Darko, additional, Balbo, Matteo, additional, Bretz, Thomas, additional, Buss, Jens, additional, Eisenberger, Laura, additional, Hildebrand, Dorothee, additional, Iotov, Roman, additional, Kalenski, Adelina, additional, Mitchell, Alison, additional, Neise, Dominik, additional, Noethe, Maximilian, additional, Paravac, Aleksander, additional, Sliusar, Vitalii, additional, Walter, Roland, additional, Valverde, J., additional, Horan, D., additional, Giroletti, M., additional, Perri, M., additional, Verrecchia, F., additional, Leto, C., additional, C. Sadun, A., additional, W. Moody, J., additional, Joner, M., additional, P. Marscher, A., additional, G. Jorstad, S., additional, Lähteenmäki, A., additional, ~Tornikoski, M., additional, Ramakrishnan, V., additional, Järvelä, E., additional, J. C. Vera, R., additional, Righini, S., additional, and Y. Lien, A., additional

Published
2021
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14. Periodicity Analysis of Mrk 501 and Mrk 421 in Gamma Rays

Author

Iotov, Roman, primary, Arbet-Engels, Axel, additional, Arras, Phillip, additional, Baack, Dominik, additional, Balbo, Matteo, additional, Biland, Adrian, additional, Boettcher, Manuel, additional, Bretz, Thomas, additional, Buss, Jens, additional, Dorner, Daniela, additional, Eberle, Vincent, additional, Eisenberger, Laura, additional, Elsaesser, Dominik, additional, Enßlin, Torsten, additional, Hildebrand, Dorothee, additional, Kalenski, Adelina, additional, Kostić, Andrija, additional, Kreter, Michael, additional, Mannheim, Karl, additional, Marchenko, Volodymyr, additional, Mitchell, Alison, additional, Neise, Dominik, additional, Noethe, Maximilian, additional, Paravac, Aleksander, additional, Rhode, Wolfgang, additional, Schleicher, Bernd, additional, Sliusar, Vitalii, additional, Tarnopolski, Mariusz, additional, Theissen, Fabian, additional, Zywucka, Natalia, additional, and Walter, Roland, additional

Published
2021
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15. FACT - Highlights from more than Eight Years of Unbiased TeV Monitoring

Author

Dorner, Daniela, primary, Arbet-Engels, Axel, additional, Baack, Dominik, additional, Balbo, Matteo, additional, Biland, Adrian, additional, Bretz, Thomas, additional, Buss, Jens, additional, Eisenberger, Laura, additional, Elsaesser, Dominik, additional, Hildebrand, Dorothee, additional, Iotov, Roman, additional, Kalenski, Adelina, additional, Mannheim, Karl, additional, Mitchell, Alison, additional, Neise, Dominik, additional, Noethe, Maximilian, additional, Paravac, Aleksander, additional, Rhode, Wolfgang, additional, Schleicher, Bernd, additional, Sliusar, Vitalii, additional, and Walter, Roland, additional

Published
2021
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16. FACT - Database-based Analysis and Spectrum Calculations

Author

Schleicher, Bernd, primary, Arbet-Engels, Axel, additional, Baack, Dominik, additional, Balbo, Matteo, additional, Biland, Adrian, additional, Bretz, Thomas, additional, Buss, Jens, additional, Dorner, Daniela, additional, Eisenberger, Laura, additional, Elsaesser, Dominik, additional, Hildebrand, Dorothee, additional, Iotov, Roman, additional, Kalenski, Adelina, additional, Mannheim, Karl, additional, Mitchell, Alison, additional, Neise, Dominik, additional, Noethe, Maximilian, additional, Paravac, Aleksander, additional, Rhode, Wolfgang, additional, Sliusar, Vitalii, additional, and Walter, Roland, additional

Published
2021
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17. Relentless multi-wavelength variability of Markarian 421 and Markarian 501

Author

Sliusar, Vitalii, primary, Arbet-Engels, Axel, additional, Baack, Dominik, additional, Balbo, Matteo, additional, Biland, Adrian, additional, Bretz, Thomas, additional, Buss, Jens, additional, Dorner, Daniela, additional, Eisenberger, Laura, additional, Elsaesser, Dominik, additional, Hildebrand, Dorothee, additional, Iotov, Roman, additional, Kalenski, Adelina, additional, Mannheim, Karl, additional, Mitchell, Alison, additional, Neise, Dominik, additional, Noethe, Maximilian, additional, Paravac, Aleksander, additional, Rhode, Wolfgang, additional, Schleicher, Bernd, additional, and Walter, Roland, additional

Published
2021
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18. Multi-wavelength study of Mrk 421 during a TeV flare

Author

Gokus, Andrea, primary, Kreikenbohm, Annika, additional, Leiter, Katharina, additional, Bretz, Thomas, additional, Dauser, Thomas, additional, Dorner, Daniela, additional, Eppel, Florian, additional, Hessdoerfer, Jonas, additional, Kadler, Matthias, additional, Kraus, Alex, additional, Kreter, Michael, additional, Kreykenbohm, Ingo, additional, Langejahn, Marcus, additional, Mannheim, Karl, additional, Thalhammer, Philipp, additional, Wilms, Joern, additional, Arbet-Engels, A., additional, Baack, D., additional, Balbo, M., additional, Biland, Adrian, additional, Buss, J., additional, Eisenberger, Laura, additional, Elsaesser, Dominik, additional, Hildebrand, D., additional, Iotov, Roman, additional, Kalenski, Adelina, additional, Mitchell, Alisson, additional, Neise, D., additional, Noethe, M., additional, Paravac, A., additional, Rhode, W., additional, Schleicher, Bernd, additional, Sliusar, Vitalii, additional, and Walter, R., additional

Published
2021
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19. Statistical properties of flux variations in blazar light curves at GeV and TeV energies

Author

Wagner, Sarah M., primary, Burd, Paul, additional, Dorner, Daniela, additional, Mannheim, Karl, additional, Buson, Sara, additional, Gokus, Andrea, additional, Madejski, Greg, additional, Scargle, Jeffrey, additional, Arbet-Engels, Axel, additional, Baack, Dominik, additional, Balbo, Matteo, additional, Biland, Adrian, additional, Bretz, Thomas, additional, Buss, Jens, additional, Elsaesser, Dominik, additional, Eisenberger, Laura, additional, Hildebrand, Dorothee, additional, Iotov, Roman, additional, Kalenski, Adelina, additional, Neise, Dominik, additional, Noethe, Maximilian, additional, Paravac, Aleksander, additional, Rhode, Wolfgang, additional, Schleicher, Bernd, additional, Sliusar, Vitalii, additional, and Walter, Roland, additional

Published
2021
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20. FACT - Highlights from more than Seven Years of Unbiased Monitoring at TeV Energies

Author

FACT Collaboration, Dorner, Daniela, Arbet-Engels, Axel, Baack, Dominik, Balbo, Matteo, Beck, Marvin, Biland, Adrian, Blank, Michael, Bretz, Thomas, Bruegge, Kai, Bulinski, Michael, Buss, Jens, Doerr, Manuel, Elsaesser, Dominik, Hildebrand, Dorothée, Iotov, Roman, Klinger, Marc, Mannheim, Karl, Neise, Dominik, Mueller, Sebastian A., Neronov, Andrii, Noethe, Maximilian, Paravac, Aleksander, Rhode, Wolfgang, Schleicher, Bernd, Sedlaczek, Kevin, Shukla, Amit, Sliusar, Vitalii, Tani, Laurits, Theissen, Fabian, Walter, Roland, and von Willert, Elan

Abstract

The First G-APD Cherenkov Telescope (FACT) has been monitoring TeV-blazars since October 2011. Thanks to its unbiased observing strategy, the robotic operation and the usage of solid state photosensors (SiPM, aka G-APDs), the instrument's duty cycle has been maximized and the observational gaps minimized, providing an unprecedented data sample of more than 13'800 hours of physics data, of which more than 2600 hours were taken in the past 12 months. Results of an automatic quick-look analysis are published with low latency on an open-access website. Based on this, 98 alerts and 11 astronomer's telegrams have been issued in more than five years, triggering a variety of multi-wavelength studies. Target-of-opportunity programs with X-ray satellites are in place. For example, combined gamma-ray observations (FACT, Fermi-LAT, HESS) on Mrk 501 in 2014 have been used to constrain the underlying physics processes analysing the shape of flux distributions on different time scales. A trigger to MAGIC on a high state of 1ES 2344+51.4 in 2016 reveals a very hard spectrum. The combined observations are used to study the source's extreme behaviour. Studying the long-term multi-wavelength behaviour of Mrk 421, more than 30 flares have been found in 5.5 years of data. Correlating different wavelengths, delays are determined and models are constrained. In addition to multi-wavelength studies, the unprecedented, unbiased data sample at TeV energies provides a unique chance to study the duty cycle and variability behaviour of the sources. Based on this, a search for a periodic signal has been performed., PoS: Proceedings of Science, 358, ISSN:1824-8039, 36th International Cosmic Ray Conference (ICRC 2019) - GRI - Gamma Ray Indirect

Published
2019

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