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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. The relentless variability of Mrk 421 from the TeV to the radio

Author: Arbet-Engels, Axel, Baack, Dominik, Balbo, Matteo, Biland, Adrian, Blank, Michael, Bretz, Thomas, Bruegge, Kai, Bulinski, Michael, Buss, Jens, Doerr, Manuel, Dorner, Daniela, Elsaesser, Dominik, Hildebrand, Dorothee, Mannheim, Karl, Mueller, Sebastian, Neise, Dominik, Noethe, Maximilian, Paravac, Aleksander, Rhode, Wolfgang, Schleicher, Bernd, Sedlaczek, Kevin, Shukla, Amit, Sliusar, Vitalii, Walter, Roland, and von Willert, Elan
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - Astrophysics of Galaxies
Abstract: The origin of the gamma-ray emission of the blazar Mrk 421 is still a matter of debate. We used 5.5 years of unbiased observing campaign data, obtained using the FACT telescope and the Fermi LAT detector at TeV and GeV energies, the longest and densest so far, together with contemporaneous multi-wavelength observations, to characterise the variability of Mrk 421 and to constrain the underlying physical mechanisms. We studied and correlated light curves obtained by ten different instruments and found two significant results. The TeV and X-ray light curves are very well correlated with a lag of <0.6 days. The GeV and radio (15 Ghz band) light curves are widely and strongly correlated. Variations of the GeV light curve lead those in the radio. Lepto-hadronic and purely hadronic models in the frame of shock acceleration predict proton acceleration or cooling timescales that are ruled out by the short variability timescales and delays observed in Mrk 421. Instead the observations match the predictions of leptonic models., Comment: 10 pages, 8 figures, 1 table
Published: 2021
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6. 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

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

Author: Sliusar, Vitalii, Arbet-Engels, Axel, Baack, Dominik, Balbo, Matteo, Biland, Adrian, Blank, Michael, Bretz, Tomas, Bruegge, Kai, Bulinski, Michael, Buss, Jens, Doerr, Manuel, Dorner, Daniela, Elsaesser, Dominik, Hildebrand, Dorothee, Mannheim, Karl, mueller, Sebastian, Neise, Dominik, Noethe, Maximilian, Paravac, Aleksander, Rhode, Wolfgang, Schleicher, Bernd, Sedlaczek, Kevin, Shukla, Amit, Walter, Roland, and von Willert, Elan
Subjects: Astrophysics - High Energy Astrophysical Phenomena
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., Comment: 9 pages, 3 figures, 1 table. 36th International Cosmic Ray Conference (ICRC2019), July 24th-August 1st, 2019. Madison, WI, U.S.A
Published: 2019

8. First Study of Combined Blazar Light Curves with FACT and HAWC

Author: Dorner, Daniela, Lauer, Robert J., Adam, Jan, Ahnen, Max, Baack, Dominik, Balbo, Matteo, Bergmann, Matthias, Biland, Adrian, Blank, Michael, Bretz, Thomas, Brügge, Kai, Buss, Jens, Dmytiiev, Anton, Einecke, Sabrina, Hempfling, Christina, Hildebrand, Dorothee, Hughes, Gareth, Linhoff, Lena, Mannheim, Karl, Müller, Sebastian, Neise, Dominik, Neronov, Andrii, Noethe, Maximilian, Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Shukla, Amit, Temme, Fabian, Thaele, Julia, and Walter, Roland
Subjects: Astrophysics - High Energy Astrophysical Phenomena
Abstract: For studying variable sources like blazars, it is crucial to achieve unbiased monitoring, either with dedicated telescopes in pointing mode or survey instruments. At TeV energies, the High Altitude Water Cherenkov (HAWC) observatory monitors approximately two thirds of the sky every day. It uses the water Cherenkov technique, which provides an excellent duty cycle independent of weather and season. The First G-APD Cherenkov Telescope (FACT) monitors a small sample of sources with better sensitivity, using the imaging air Cherenkov technique. Thanks to its camera with silicon-based photosensors, FACT features an excellent detector performance and stability and extends its observations to times with strong moonlight, increasing the duty cycle compared to other imaging air Cherenkov telescopes. As FACT and HAWC have overlapping energy ranges, a joint study can exploit the longer daily coverage given that the observatories' locations are offset by 5.3 hours. Furthermore, the better sensitivity of FACT adds a finer resolution of features on hour-long time scales, while the continuous duty cycle of HAWC ensures evenly sampled long-term coverage. Thus, the two instruments complement each other to provide a more complete picture of blazar variability. In this presentation, the first joint study of light curves from the two instruments will be shown, correlating long-term measurements with daily sampling between air and water Cherenkov telescopes. The presented results focus on the study of the variability of the bright blazars Mrk 421 and Mrk 501 during the last two years featuring various flaring activities., Comment: 6 pages, 2 figures. Contribution to the 6th International Symposium on High Energy Gamma-Ray Astronomy (Gamma2016), Heidelberg, Germany. To be published in the AIP Conference Proceedings
Published: 2016
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9. 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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10. 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

11. 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

12. 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

13. 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

14. 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

15. 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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16. 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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17. 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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18. 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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19. 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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20. 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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21. 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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22. 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

23. Fractional Variability : A Tool to Study Blazar Variability

Author: Schleicher, Bernd, Arbet-Engels, Axel, Baack, Dominik, Balbo, Matteo, Biland, Adrian, Blank, Michael, Bretz, Thomas Günther, Bruegge, Kai, Bulinski, Michael, Buss, Jens, Doerr, Manuel, Dorner, Daniela, Elsaesser, Dominik, Grischagin, Sergej, Hildebrand, Dorothee, Linhoff, Lena, Mannheim, Karl, Mueller, Sebastian, Neise, Dominik, Neronov, Andrii, Noethe, Maximilian, Paravac, Aleksander, Rhode, Wolfgang, Schulz, Florian, Sedlaczek, Kevin, Shukla, Amit, Sliusar, Vitalii, Willert, Elan, and Walter, Roland
Subjects: ddc:520
Abstract: Galaxies 7(2), 62 (2019). doi:10.3390/galaxies7020062 special issue: "Special Issue "Monitoring the Non-Thermal Universe" / Guest Editors Dr. Daniela Dorner Department of Astronomy, University Würzburg, Prof. Dr. Thomas Bretz RWTH Aachen University", Published by MDPI, Basel
Published: 2019
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24. Flux States of Active Galactic Nuclei

Author: Dorner, Daniela, Arbet-Engels, Axel, Baack, Dominik, Balbo, Matteo, Biland, Adrian, Blank, Michael, Bretz, Thomas, Bruegge, Kai, Bulinski, Michael, Buss, Jens, Doerr, Manuel, Elsaesser, Dominik, Hildebrand, Dorothée, Linhoff, Lena, Mannheim, Karl, Mueller, Sebastian A., Neise, Dominik, Neronov, Andrii, Noethe, Maximilian, Paravac, Aleksander, Rhode, Wolfgang, Schleicher, Bernd, Schulz, Florian, Sedlaczek, Kevin, Shukla, Amit, Sliusar, Vitalii, von Willert, Elan, Walter, Roland, FACT Collaboration, Dorner, Daniela, Balbo, Matteo, Blank, Michael, Neronov, Andrii, Sliusar, Vitalii, and Walter, Roland
Subjects: Active galactic nucleus, flux distributions, Monitoring, lcsh:Astronomy, blazars, FACT, Flux, Astrophysics, active galactic nuclei, monitoring, TeV energies, flux states, duty cycle, 01 natural sciences, law.invention, Telescope, lcsh:QB1-991, law, 0103 physical sciences, Range (statistics), Blazar, 010303 astronomy & astrophysics, Cherenkov radiation, Physics, Duty cycle, Active galactic nuclei, 010308 nuclear & particles physics, Flux distributions, Astronomy and Astrophysics, Galaxy, Flux states, ddc:520, Blazars
Abstract: Blazars are known to show variability on time scales from minutes to years covering a wide range of flux states. Studying the flux distribution of a source allows for various insights. The shape of the flux distribution can provide information on the nature of the underlying variability processes. The level of a possible quiescent state can be derived from the main part of the distribution that can be described by a Gaussian distribution. Dividing the flux states into quiescent and active, the duty cycle of a source can be calculated. Finally, this allows alerting the multi-wavelength and multi-messenger community in case a source is in an active state. To get consistent and conclusive results from flux distributions, unbiased long-term observations are crucial. Only like this is a complete picture of the variability and flux states, e.g., an all-time quiescent state, possible. In seven years of monitoring of bright TeV blazars, the first G-APD Cherenkov telescope (FACT) has collected a total of more than 11,700 hours of physics data with 1500 hours to 3000 hours per source for Mrk 421, Mrk 501, 1ES 1959+650, and 1ES 2344+51., Galaxies;7(2)
Published: 2019
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25. Fractional Variability—A Tool to Study Blazar Variability

Author: Schleicher, Bernd, primary, Arbet-Engels, Axel, additional, Baack, Dominik, additional, Balbo, Matteo, additional, Biland, Adrian, additional, Blank, Michael, additional, Bretz, Thomas, additional, Bruegge, Kai, additional, Bulinski, Michael, additional, Buss, Jens, additional, Doerr, Manuel, additional, Dorner, Daniela, additional, Elsaesser, Dominik, additional, Grischagin, Sergej, additional, Hildebrand, Dorothee, additional, Linhoff, Lena, additional, Mannheim, Karl, additional, Mueller, Sebastian, additional, Neise, Dominik, additional, Neronov, Andrii, additional, Noethe, Maximilian, additional, Paravac, Aleksander, additional, Rhode, Wolfgang, additional, Schulz, Florian, additional, Sedlaczek, Kevin, additional, Shukla, Amit, additional, Sliusar, Vitalii, additional, Willert, Elan, additional, and Walter, Roland, additional
Published: 2019
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26. Measuring the Optical Point Spread Function of FACT Using the Cherenkov Camera

Author: Noethe, Maximilian, primary, Adam, J., additional, Ahnen, Max Ludwig, additional, Baack, D., additional, Balbo, Matteo, additional, Biland, Adrian, additional, Blank, M., additional, Bretz, Thomas, additional, Bruegge, K, additional, Buss, Jens, additional, Dmytriiev, A., additional, Dorner, Daniela, additional, Einecke, Sabrina, additional, Elsaesser, Dominik, additional, Hempfling, Christina, additional, Herbst, Tina, additional, Hildebrand, Dorothee, additional, Kortmann, L., additional, Linhoff, L., additional, Mahlke, Max, additional, Mannheim, Karl, additional, mueller, Sebastian, additional, Neise, Dominik, additional, Neronov, Andrii, additional, Oberkirch, J., additional, Paravac, Aleksander, additional, Pauss, Felicitas, additional, Rhode, Wolfgang, additional, Schleicher, B., additional, Schulz, F., additional, Shukla, Amit, additional, Sliusar, Vitalii, additional, Temme, Fabian, additional, Thaele, Julia, additional, and Walter, Roland, additional
Published: 2017
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27. FACT – Performance of the First Cherenkov Telescope Observing with SiPMs

Author: Noethe, Maximilian, primary, Adam, J., additional, Ahnen, Max Ludwig, additional, Baack, D., additional, Balbo, Matteo, additional, Biland, Adrian, additional, Blank, M., additional, Bretz, Thomas, additional, Bruegge, K, additional, Buss, Jens, additional, Dmytriiev, A., additional, Dorner, Daniela, additional, Einecke, Sabrina, additional, Elsaesser, Dominik, additional, Hempfling, Christina, additional, Herbst, Tina, additional, Hildebrand, Dorothee, additional, Kortmann, L., additional, Linhoff, L., additional, Mahlke, Max, additional, Mannheim, Karl, additional, mueller, Sebastian, additional, Neise, Dominik, additional, Neronov, Andrii, additional, Oberkirch, J., additional, Paravac, Aleksander, additional, Pauss, Felicitas, additional, Rhode, Wolfgang, additional, Schleicher, B., additional, Schulz, F., additional, Shukla, Amit, additional, Sliusar, Vitalii, additional, Temme, Fabian, additional, Thaele, Julia, additional, and Walter, Roland, additional
Published: 2017
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28. Higher Order Temperature Dependence of SiPM used in FACT

Author: Hildebrand, Dorothee, primary, Ahnen, Max Ludwig, additional, Adam, J., additional, Balbo, Matteo, additional, Biland, Adrian, additional, Baack, D., additional, Bretz, Thomas, additional, Buss, Jens, additional, Blank, M., additional, Einecke, Sabrina, additional, Bruegge, K, additional, Dorner, Daniela, additional, Elsaesser, Dominik, additional, Hempfling, Christina, additional, Herbst, Tina, additional, Mahlke, Max, additional, Mannheim, Karl, additional, Neise, Dominik, additional, Neronov, Andrii, additional, Noethe, Maximilian, additional, Paravac, Aleksander, additional, Pauss, Felicitas, additional, Rhode, Wolfgang, additional, Sliusar, Vitalii, additional, Temme, Fabian, additional, Thaele, Julia, additional, Kortmann, L., additional, Dmytriiev, A., additional, Linhoff, L., additional, Mueller, Sebastian, additional, Oberkirch, J., additional, Schleicher, B., additional, Schulz, F., additional, and Shukla, Amit, additional
Published: 2017
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29. Using Charged Cosmic Ray Particles to Monitor the Data Quality of FACT

Author: Hildebrand, Dorothee, primary, Ahnen, Max Ludwig, additional, Balbo, Matteo, additional, Biland, Adrian, additional, Bretz, Thomas, additional, Buss, Jens, additional, Dorner, Daniela, additional, Einecke, Sabrina, additional, Elsaesser, Dominik, additional, Herbst, Tina, additional, Mahlke, Max, additional, Mannheim, Karl, additional, Neise, Dominik, additional, Neronov, Andrii, additional, Noethe, Maximilian, additional, Paravac, Aleksander, additional, Pauss, Felicitas, additional, Rhode, Wolfgang, additional, Sliusar, Vitalii, additional, Temme, Fabian, additional, Walter, Roland, additional, Adam, J., additional, Baack, D., additional, Blank, M., additional, Bruegge, K, additional, Dmytriiev, A., additional, Hempfling, Christina, additional, Kortmann, L., additional, Linhoff, L., additional, Oberkirch, J., additional, Schleicher, B., additional, Schulz, F., additional, Shukla, Amit, additional, Thaele, Julia, additional, and Mueller, S A, additional
Published: 2017
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30. Single Photon Extraction for FACT’s SiPMs allows for Novel IACT Event Representation

Author: Mueller, Sebastian Achim, primary, Adam, J., additional, Ahnen, Max Ludwig, additional, Baack, D., additional, Balbo, Matteo, additional, Biland, Adrian, additional, Blank, M., additional, Bretz, Thomas, additional, Bruegge, K, additional, Buss, Jens, additional, Dmytriiev, A., additional, Dorner, Daniela, additional, Einecke, Sabrina, additional, Elsaesser, Dominik, additional, Hempfling, Christina, additional, Herbst, Tina, additional, Hildebrand, Dorothee, additional, Kortmann, L., additional, Linhoff, L., additional, Mahlke, Max, additional, Mannheim, Karl, additional, Neise, Dominik, additional, Neronov, Andrii, additional, Noethe, Maximilian, additional, Oberkirch, J., additional, Paravac, Aleksander, additional, Pauss, Felicitas, additional, Rhode, Wolfgang, additional, Schleicher, B., additional, Schulz, F., additional, Shukla, Amit, additional, Sliusar, Vitalii, additional, Temme, Fabian, additional, Thaele, Julia, additional, and Walter, Roland, additional
Published: 2017
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31. Long-Term Monitoring of Bright Blazars in the Multi-GeV to TeV Range with FACT

Author: Temme, Fabian, primary, Adam, Jan, additional, Ahnen, Max, additional, Baack, Dominik, additional, Balbo, Matteo, additional, Bergmann, Matthias, additional, Biland, Adrian, additional, Blank, Michael, additional, Bretz, Thomas, additional, Brügge, Kai, additional, Buss, Jens, additional, Dmytriiev, Anton, additional, Dorner, Daniela, additional, Einecke, Sabrina, additional, Hempfling, Christina, additional, Hildebrand, Dorothee, additional, Hughes, Gareth, additional, Linhoff, Lena, additional, Mannheim, Karl, additional, Müller, Sebastian, additional, Neise, Dominik, additional, Neronov, Andrii, additional, Nöthe, Max, additional, Paravac, Aleksander, additional, Pauss, Felicitas, additional, Rhode, Wolfgang, additional, Shukla, Amit, additional, Thaele, Julia, additional, and Walter, Roland, additional
Published: 2017
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32. Normalized and asynchronous mirror alignment for Cherenkov telescopes

Author: Ahnen, Max M.L., Baack, Dominik, Balbo, Matteo, Bergmann, Matthias, Biland, Adrian, Blank, Michael, Bretz, Thomas, Bruegge, Kai K.A., Buss, Jens, Domke, M., Dorner, Daniela, Einecke, Sabrina, Hempfling, Christina, Hildebrand, Dorothée, Hughes, Gareth, Lustermann, Werner, Mannheim, Karl, Mueller, Sebastian Achim, Neise, Dominik, Neronov, Andrii, Noethe, Maximilian, Overkemping, A.K., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Shukla, Amit, Temme, Fabian, Thaele, Julia, Toscano, Simona, Vogler, Patrick, Walter, Roland, Wilbert, A., Ahnen, Max M.L., Baack, Dominik, Balbo, Matteo, Bergmann, Matthias, Biland, Adrian, Blank, Michael, Bretz, Thomas, Bruegge, Kai K.A., Buss, Jens, Domke, M., Dorner, Daniela, Einecke, Sabrina, Hempfling, Christina, Hildebrand, Dorothée, Hughes, Gareth, Lustermann, Werner, Mannheim, Karl, Mueller, Sebastian Achim, Neise, Dominik, Neronov, Andrii, Noethe, Maximilian, Overkemping, A.K., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Shukla, Amit, Temme, Fabian, Thaele, Julia, Toscano, Simona, Vogler, Patrick, Walter, Roland, and Wilbert, A.
Abstract: Imaging Atmospheric Cherenkov Telescopes (IACTs) need imaging optics with large apertures and high image intensities to map the faint Cherenkov light emitted from cosmic ray air showers onto their image sensors. Segmented reflectors fulfill these needs, and as they are composed from mass production mirror facets they are inexpensive and lightweight. However, as the overall image is a superposition of the individual facet images, alignment is a challenge. Here we present a computer vision based star tracking alignment method, which also works for limited or changing star light visibility. Our method normalizes the mirror facet reflection intensities to become independent of the reference star's intensity or the cloud coverage. Using two CCD cameras, our method records the mirror facet orientations asynchronously of the telescope drive system, and thus makes the method easy to integrate into existing telescopes. It can be combined with remote facet actuation, but does not require one to work. Furthermore, it can reconstruct all individual mirror facet point spread functions without moving any mirror. We present alignment results on the 4 m First Geiger-mode Avalanche Cherenkov Telescope (FACT)., SCOPUS: ar.j, info:eu-repo/semantics/published
Published: 2016

33. Bokeh mirror alignment for Cherenkov telescopes

Author: Ahnen, Max M.L., Baack, Dominik, Balbo, Matteo, Bergmann, Matthias, Biland, Adrian, Blank, Michael, Bretz, Thomas, Bruegge, Kai K.A., Buss, Jens, Domke, M., Dorner, Daniela, Einecke, Sabrina, Hempfling, Christina, Hildebrand, Dorothée, Hughes, Gareth, Lustermann, Werner, Mannheim, Karl, Mueller, Sebastian Achim, Neise, Dominik, Neronov, Andrii, Noethe, Maximilian, Overkemping, A.K., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Shukla, Amit, Temme, Fabian, Thaele, Julia, Toscano, Simona, Vogler, Patrick, Walter, Roland, Wilbert, A., Ahnen, Max M.L., Baack, Dominik, Balbo, Matteo, Bergmann, Matthias, Biland, Adrian, Blank, Michael, Bretz, Thomas, Bruegge, Kai K.A., Buss, Jens, Domke, M., Dorner, Daniela, Einecke, Sabrina, Hempfling, Christina, Hildebrand, Dorothée, Hughes, Gareth, Lustermann, Werner, Mannheim, Karl, Mueller, Sebastian Achim, Neise, Dominik, Neronov, Andrii, Noethe, Maximilian, Overkemping, A.K., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Shukla, Amit, Temme, Fabian, Thaele, Julia, Toscano, Simona, Vogler, Patrick, Walter, Roland, and Wilbert, A.
Abstract: Imaging Atmospheric Cherenkov Telescopes (IACTs) need imaging optics with large apertures and high image intensities to map the faint Cherenkov light emitted from cosmic ray air showers onto their image sensors. Segmented reflectors fulfill these needs, and composed from mass production mirror facets they are inexpensive and lightweight. However, as the overall image is a superposition of the individual facet images, alignment remains a challenge. Here we present a simple, yet extendable method, to align a segmented reflector using its Bokeh. Bokeh alig nment does not need a star or good weather nights but can be done even during daytime. Bokeh alignment optimizes the facet orientations by comparing the segmented reflectors Bokeh to a predefined template. The optimal Bokeh template is highly constricted by the reflector's aperture and is easy accessible. The Bokeh is observed using the out of focus image of a near by point like light source in a distance of about 10 focal lengths. We introduce Bokeh alignment on segmented reflectors and demonstrate it on the First Geiger-mode Avalanche Cherenkov Telescope (FACT) on La Palma, Spain., SCOPUS: ar.j, info:eu-repo/semantics/published
Published: 2016

34. FACT - Performance of the First SiPM camera

Author: Neise, Dominik, primary, Ahnen, Max Ludwig, additional, Balbo, Matteo, additional, Bergmann, Matthias, additional, Biland, Adrian, additional, Bretz, Thomas, additional, Brügge, Kai Arno, additional, Buss, Jens, additional, Dorner, Daniela, additional, Einecke, Sabrina, additional, Freiwald, Jan, additional, Hempfling, Christina, additional, Hildebrand, Dorothee, additional, Hughes, Gareth, additional, Lustermann, Werner, additional, Mannheim, Karl, additional, Meier, Katja, additional, Mueller, Sebastian Achim, additional, Neronov, Andrii, additional, Noethe, Maximilian, additional, Overkemping, Ann-Kristin, additional, Paravac, Aleksander, additional, Pauss, Felicitas, additional, Rhode, Wolfgang, additional, Temme, Fabian, additional, Thaele, Julia, additional, Toscano, Simona, additional, Vogler, Patrick, additional, Walter, Roland, additional, and Wilbert, Aylin, additional
Published: 2016
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35. FACT -- Novel mirror alignment using Bokeh and enhancement of the VERITAS SCCAN alignment method

Author: Mueller, Sebastian Achim, primary, Ahnen, Max Ludwig, additional, Balbo, Matteo, additional, Bergmann, Matthias, additional, Biland, Adrian, additional, Bretz, Thomas, additional, Buss, Jens, additional, Dorner, Daniela, additional, Einecke, Sabrina, additional, Freiwald, Jan, additional, Hempfling, Christina, additional, Hildebrand, Dorothee, additional, Hughes, Gareth, additional, Lustermann, Werner, additional, Mannheim, Karl, additional, Meier, Katja, additional, Neise, Dominik, additional, Neronov, Andrii, additional, Noethe, Maximilian, additional, Overkemping, Ann-Kristin, additional, Paravac, Aleksander, additional, Pauss, Felicitas, additional, Rhode, Wolfgang, additional, Temme, Fabian, additional, Thaele, Julia, additional, Toscano, Simona, additional, Vogler, Patrick, additional, Walter, Roland, additional, and Wilbert, Aylin, additional
Published: 2016
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36. FACT - Status and Experience from Three Years Operation of the First SiPM Camera

Author: Biland, Adrian, primary, Ahnen, Max Ludwig, additional, Balbo, Matteo, additional, Bergmann, Matthias, additional, Bretz, Thomas, additional, Brügge, Kai Arno, additional, Buss, Jens, additional, Dorner, Daniela, additional, Einecke, Sabrina, additional, Freiwald, Jan, additional, Hempfling, Christina, additional, Hildebrand, Dorothee, additional, Hughes, Gareth, additional, Lustermann, Werner, additional, Mannheim, Karl, additional, Meier, Katja, additional, Mueller, Sebastian Achim, additional, Neise, Dominik, additional, Neronov, Andrii, additional, Noethe, Maximilian, additional, Overkemping, Ann-Kristin, additional, Paravac, Aleksander, additional, Pauss, Felicitas, additional, Rhode, Wolfgang, additional, Temme, Fabian, additional, Thaele, Julia, additional, Toscano, Simona, additional, Vogler, Patrick, additional, Walter, Roland, additional, and Wilbert, Aylin, additional
Published: 2016
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37. FACT - First Energy Spectrum from a SiPM Cherenkov Telescope

Author: Temme, Fabian, primary, Ahnen, Max Ludwig, additional, Balbo, Matteo, additional, Bergmann, Matthias, additional, Biland, Adrian, additional, Bockermann, Christian, additional, Bretz, Thomas, additional, Brügge, Kai Arno, additional, Buss, Jens, additional, Dorner, Daniela, additional, Einecke, Sabrina, additional, Freiwald, Jan, additional, Hempfling, Christina, additional, Hildebrand, Dorothee, additional, Hughes, Gareth, additional, Lustermann, Werner, additional, Mannheim, Karl, additional, Meier, Katja, additional, Morik, Katharina, additional, Mueller, Sebastian Achim, additional, Neise, Dominik, additional, Neronov, Andrii, additional, Noethe, Maximilian, additional, Overkemping, Ann-Kristin, additional, Paravac, Aleksander, additional, Pauss, Felicitas, additional, Rhode, Wolfgang, additional, Thaele, Julia, additional, Toscano, Simona, additional, Vogler, Patrick, additional, Walter, Roland, additional, and Wilbert, Aylin, additional
Published: 2016
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38. FACT - TeV Flare Alerts Triggering Multi-Wavelength Observations

Author: Dorner, Daniela, primary, Ahnen, Max Ludwig, additional, Balbo, Matteo, additional, Bergmann, Matthias, additional, Biland, Adrian, additional, Bretz, Thomas, additional, Brügge, Kai Arno, additional, Buss, Jens, additional, Einecke, Sabrina, additional, Freiwald, Jan, additional, Hempfling, Christina, additional, Hildebrand, Dorothee, additional, Hughes, Gareth, additional, Lustermann, Werner, additional, Mannheim, Karl, additional, Meier, Katja, additional, Mueller, Sebastian Achim, additional, Neise, Dominik, additional, Neronov, Andrii, additional, Noethe, Maximilian, additional, Overkemping, Ann-Kristin, additional, Paravac, Aleksander, additional, Pauss, Felicitas, additional, Rhode, Wolfgang, additional, Temme, Fabian, additional, Thaele, Julia, additional, Toscano, Simona, additional, Vogler, Patrick, additional, Walter, Roland, additional, and Wilbert, Aylin, additional
Published: 2016
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39. FACT - Calibration of Imaging Atmospheric Cerenkov Telescopes with Muon Rings

Author: Noethe, Maximilian, primary, Ahnen, Max Ludwig, additional, Balbo, Matteo, additional, Bergmann, Matthias, additional, Biland, Adrian, additional, Bockermann, Christian, additional, Bretz, Thomas, additional, Brügge, Kai Arno, additional, Buss, Jens, additional, Dorner, Daniela, additional, Einecke, Sabrina, additional, Freiwald, Jan, additional, Hempfling, Christina, additional, Hildebrand, Dorothee, additional, Hughes, Gareth, additional, Lustermann, Werner, additional, Mannheim, Karl, additional, Meier, Katja, additional, Morik, Katharina, additional, Mueller, Sebastian Achim, additional, Neise, Dominik, additional, Neronov, Andrii, additional, Overkemping, Ann-Kristin, additional, Paravac, Aleksander, additional, Pauss, Felicitas, additional, Rhode, Wolfgang, additional, Temme, Fabian, additional, Thaele, Julia, additional, Toscano, Simona, additional, Vogler, Patrick, additional, Walter, Roland, additional, and Wilbert, Aylin, additional
Published: 2016
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40. FACT – Influence of SiPM Crosstalk on the Performance of an Operating Cherenkov Telescope

Author: Buss, Jens, primary, Ahnen, Max Ludwig, additional, Balbo, Matteo, additional, Biland, Adrian, additional, Bockermann, Christian, additional, Bretz, Thomas, additional, Brügge, Kai Arno, additional, Dorner, Daniela, additional, Einecke, Sabrina, additional, Freiwald, Jan, additional, Hempfling, Christina, additional, Hughes, Gareth, additional, Hildebrand, Dorothee, additional, Lustermann, Werner, additional, Mannheim, Karl, additional, Meier, Katja, additional, Morik, Katharina, additional, Mueller, Sebastian Achim, additional, Neise, Dominik, additional, Neronov, Andrii, additional, Noethe, Maximilian, additional, Overkemping, Ann-Kristin, additional, Paravac, Aleksander, additional, Pauss, Felicitas, additional, Rhode, Wolfgang, additional, Temme, Fabian, additional, Thaele, Julia, additional, Toscano, Simona, additional, Vogler, Patrick, additional, Walter, Roland, additional, and Wilbert, Aylin, additional
Published: 2016
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41. FACT-Tools: Streamed Real-Time Data Analysis

Author: Brügge, Kai Arno, primary, Ahnen, Max Ludwig, additional, Balbo, Matteo, additional, Bergmann, Matthias, additional, Buss, Jens, additional, Biland, Adrian, additional, Bockermann, Christian, additional, Bretz, Thomas, additional, Dorner, Daniela, additional, Freiwald, Jan, additional, Einecke, Sabrina, additional, Toscano, Simona, additional, Thaele, Julia, additional, Temme, Fabian, additional, Hempfling, Christina, additional, Hildebrand, Dorothee, additional, Hughes, Gareth, additional, Lustermann, Werner, additional, Mannheim, Karl, additional, Meier, K., additional, Morik, Katharina, additional, Neise, Dominik, additional, Mueller, Sebastian Achim, additional, Neronov, Andrii, additional, Noethe, Maximilian, additional, Overkemping, Ann-Kristin, additional, Paravac, Aleksander, additional, Pauss, Felicitas, additional, Walter, Roland, additional, Wilbert, Aylin, additional, Rhode, Wolfgang, additional, and Vogler, Patrick, additional
Published: 2016
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42. FACT - Calibration of imaging atmospheric cherenkov telescopes with muon rings

Author: Nöthe, Max, Ahnen, Max M.L., Balbo, Matteo, Bergmann, Matthias, Bockermann, Christian, Biland, Adrian, Bretz, Thomas, Brügge, Kai K.A., Buss, Jens, Dorner, Daniela, Einecke, Sabrina, Freiwald, J., Hempfling, Christina, Hildebrand, Dorothée, Hughes, Gareth, Lustermann, Werner, Mannheim, Karl, Meier, Katja, Morik, Katharina, Müller, Sebastian, Neise, Dominik, Neronov, Andrii, Overkemping, A.K., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Temme, Fabian, Thaele, Julia, Toscano, Simona, Vogler, Patrick, Walter, Roland, Wilbert, A., Nöthe, Max, Ahnen, Max M.L., Balbo, Matteo, Bergmann, Matthias, Bockermann, Christian, Biland, Adrian, Bretz, Thomas, Brügge, Kai K.A., Buss, Jens, Dorner, Daniela, Einecke, Sabrina, Freiwald, J., Hempfling, Christina, Hildebrand, Dorothée, Hughes, Gareth, Lustermann, Werner, Mannheim, Karl, Meier, Katja, Morik, Katharina, Müller, Sebastian, Neise, Dominik, Neronov, Andrii, Overkemping, A.K., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Temme, Fabian, Thaele, Julia, Toscano, Simona, Vogler, Patrick, Walter, Roland, and Wilbert, A.
Abstract: The First G-APD Cherenkov Telescope (FACT) is an Imaging Air Cherenkov Telescope (IACT) located on the Canary Island of La Palma. Its goal is to provide long term monitoring of cosmic objects like Active Galactic Nuclei. FACT is the first IACT to use Silicon Photomultipliers instead of conventional Photo Multiplier Tubes. Therefore studying the detector properties is especially important. Muon Rings are an event class that can offer valuable insight into the detector. These images are created by single muons that hit the mirror of the telescope. Due to their unique shape, one can use pattern recognition techniques like the Hough-Transform to identify these events. The well-known properties of muon rings and their small photon arrival time distribution allow to estimate the time resolution, photon detection efficiency and optical Point-Spread-Function of the telescope. In this contribution, the multivariate method using a random forest to extract muons from FACT data will be presented. Also the first results, including the time resolution of FACT and the impact of the mirror alignment in May 2014 on the ring width of muon events, are shown., SCOPUS: cp.p, info:eu-repo/semantics/published
Published: 2015

43. FACT - Novel mirror alignment using bokeh and enhancement of the VERITAS SCCAN alignment method

Author: Müller, Sebastian, Ahnen, Max M.L., Balbo, Matteo, Bergmann, Matthias, Biland, Adrian, Bretz, Thomas, Brügge, Kai K.A., Buss, Jens, Dorner, Daniela, Einecke, Sabrina, Freiwald, J., Hempfling, Christina, Hildebrand, Dorothée, Hughes, Gareth, Lustermann, Werner, Mannheim, Karl, Meier, Katja, Neise, Dominik, Neronov, Andrii, Nöthe, Max, Overkemping, A.K., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Temme, Fabian, Thaele, Julia, Toscano, Simona, Vogler, Patrick, Walter, Roland, Wilbert, A., Müller, Sebastian, Ahnen, Max M.L., Balbo, Matteo, Bergmann, Matthias, Biland, Adrian, Bretz, Thomas, Brügge, Kai K.A., Buss, Jens, Dorner, Daniela, Einecke, Sabrina, Freiwald, J., Hempfling, Christina, Hildebrand, Dorothée, Hughes, Gareth, Lustermann, Werner, Mannheim, Karl, Meier, Katja, Neise, Dominik, Neronov, Andrii, Nöthe, Max, Overkemping, A.K., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Temme, Fabian, Thaele, Julia, Toscano, Simona, Vogler, Patrick, Walter, Roland, and Wilbert, A.
Abstract: Imaging Air Cherenkov Telescopes, including the First G-APD Cherenkov Telescope (FACT), use segmented reflectors. These offer large and fast apertures for little resources. However, one challenge is the alignment of the mirrors to gain a sharp image. For Cherenkov telescopes, high spatial and temporal resolution is crucial to reconstruct air shower events. Therefore one has to align the individual mirror positions and orientations precisely. Alignment is difficult due to the large number of degrees of freedom and, because most techniques involve a star, has to be done during good weather nights which overlaps with observation time. We present the mirror alignment of FACT, done using two methods. Firstly, we show a new method which we call Bokeh alignment. This method is simple, cheap and can even be done during daytime. Secondly, we demonstrate an enhancement of the SCCAN method by F. Arqueros et al. and first implemented by the McGill VERITAS group. Using a second camera, our enhanced SCCAN is optimized for changing weather, changing zenith distance, and changing reference stars. Developed off site in the lab on a 1/10th scale model of FACT, both our methods resulted in a highly telescope independent procedure, e.g. both our methods run without communication to the telescope's drive. We compare alignment results by using the point spread function of star images, ray tracing simulations, and overall muon rates before and after the alignment., SCOPUS: cp.p, info:eu-repo/semantics/published
Published: 2015

44. FACT - Influence of sipm crosstalk on the performance of an operating cherenkov telescope

Author: Buss, Jens, Ahnen, Max M.L., Balbo, Matteo, Bergmann, Matthias, Biland, Adrian, Bockermann, Christian, Bretz, Thomas, Brügge, Kai K.A., Dorner, Daniela, Einecke, Sabrina, Freiwald, J., Hempfling, Christina, Hildebrand, Dorothée, Hughes, Gareth, Lustermann, Werner, Mannheim, Karl, Meier, Katja, Müller, Sebastian, Neise, Dominik, Neronov, Andrii, Nöthe, Max, Overkemping, A.K., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Temme, Fabian, Thaele, Julia, Toscano, Simona, Vogler, Patrick, Walter, Roland, Wilbert, A., Buss, Jens, Ahnen, Max M.L., Balbo, Matteo, Bergmann, Matthias, Biland, Adrian, Bockermann, Christian, Bretz, Thomas, Brügge, Kai K.A., Dorner, Daniela, Einecke, Sabrina, Freiwald, J., Hempfling, Christina, Hildebrand, Dorothée, Hughes, Gareth, Lustermann, Werner, Mannheim, Karl, Meier, Katja, Müller, Sebastian, Neise, Dominik, Neronov, Andrii, Nöthe, Max, Overkemping, A.K., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Temme, Fabian, Thaele, Julia, Toscano, Simona, Vogler, Patrick, Walter, Roland, and Wilbert, A.
Abstract: The First G-APD Cherenkov Telescope (FACT) is the first operational telescope of its kind, employing a camera equipped with silicon photon detectors (G-APD aka. SiPM). SiPMs have a high photon detection efficiency (PDE), while being more robust to bright light conditions than the commonly used photo-multiplier tubes. This technology has allowed us to increase the duty cycle beyond that of the current generation of imaging air Cherenkov telescopes. During the last four years, the operation of FACT has proven that SiPMs are a suitable photon detectors for an application in the field of ground-based gamma-ray astronomy. Nevertheless, it has been argued that crosstalk, after-pulses and dark counts are the main drawback of SiPMs, as these effects produce photon-like signals that would add up the signal background. Consequently, it is necessary to understand their impact on the analysis of data from FACT. In this contribution, we will show the current status of a study about the influence of different settings of crosstalk and dark counts on the performance of FACT. For that purpose, Monte Carlo simulations are used and compared to the actual data from the SiPM camera of FACT., SCOPUS: cp.p, info:eu-repo/semantics/published
Published: 2015

45. FACT - First energy spectrum from a SiPM cherenkov telescope

Author: Temme, Fabian, Ahnen, Max M.L., Balbo, Matteo, Bergmann, Matthias, Biland, Adrian, Bockermann, Christian, Bretz, Thomas, Brügge, Kai K.A., Buss, Jens, Dorner, Daniela, Einecke, Sabrina, Freiwald, J., Hempfling, Christina, Hildebrand, Dorothée, Hughes, Gareth, Lustermann, Werner, Mannheim, Karl, Meier, Katja, Morik, Katharina, Müller, Sebastian, Neise, Dominik, Neronov, Andrii, Nöthe, Max, Overkemping, A.K., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Thaele, Julia, Toscano, Simona, Vogler, Patrick, Walter, Roland, Wilbert, A., Temme, Fabian, Ahnen, Max M.L., Balbo, Matteo, Bergmann, Matthias, Biland, Adrian, Bockermann, Christian, Bretz, Thomas, Brügge, Kai K.A., Buss, Jens, Dorner, Daniela, Einecke, Sabrina, Freiwald, J., Hempfling, Christina, Hildebrand, Dorothée, Hughes, Gareth, Lustermann, Werner, Mannheim, Karl, Meier, Katja, Morik, Katharina, Müller, Sebastian, Neise, Dominik, Neronov, Andrii, Nöthe, Max, Overkemping, A.K., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Thaele, Julia, Toscano, Simona, Vogler, Patrick, Walter, Roland, and Wilbert, A.
Abstract: The First G-APD Cherenkov Telescope (FACT) is an Imaging Air Cherenkov Telescope located on the Canary Island of La Palma. It is the first of its kind which uses Geiger-mode Avalanche Photo Diodes (G-APDs) as photosensors to detect the Cherenkov radiation emitted from secondary particles in a high-energy gamma-ray air shower. A new analysis chain has been developed using modern data mining methods and unfolding techniques to obtain the energy spectrum of an observed source. This analysis chain has been applied to data of the Crab Nebula, the so called 'standard candle' in Cherenkov astronomy. Here, the individual steps are described and results of this application are reported providing the energy spectrum and light curve., SCOPUS: cp.p, info:eu-repo/semantics/published
Published: 2015

46. FACT - Status and experience from three years operation of the first SiPM camera

Author: Biland, Adrian, Ahnen, Max M.L., Balbo, Matteo, Bergmann, Matthias, Bretz, Thomas, Brügge, Kai K.A., Buss, Jens, Dorner, Daniela, Einecke, Sabrina, Freiwald, J., Hempfling, Christina, Hildebrand, Dorothée, Hughes, Gareth, Lustermann, Werner, Mannheim, Karl, Meier, Katja, Müller, Sebastian, Neise, Dominik, Neronov, Andrii, Nöthe, Max, Overkemping, A.K., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Temme, Fabian, Thaele, Julia, Toscano, Simona, Vogler, Patrick, Walter, Roland, Wilbert, A., Biland, Adrian, Ahnen, Max M.L., Balbo, Matteo, Bergmann, Matthias, Bretz, Thomas, Brügge, Kai K.A., Buss, Jens, Dorner, Daniela, Einecke, Sabrina, Freiwald, J., Hempfling, Christina, Hildebrand, Dorothée, Hughes, Gareth, Lustermann, Werner, Mannheim, Karl, Meier, Katja, Müller, Sebastian, Neise, Dominik, Neronov, Andrii, Nöthe, Max, Overkemping, A.K., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Temme, Fabian, Thaele, Julia, Toscano, Simona, Vogler, Patrick, Walter, Roland, and Wilbert, A.
Abstract: The First G-APD Cherenkov Telescope (FACT) is pioneering the usage of solid state photosensors (G-APD, also known as SiPM). The 1440 pixel camera is installed in a 9.5 m2 refurbished HEGRA telescope on the Canary Island La Palma. Physics data-taking with FACT started in October 2011, a few hours after installation of the camera. Since Summer 2012, FACT is operated remotely without the need of a data-taking crew on site. During more than three years of operation of FACT, G-APDs have proven to be very reliable. Despite operating them regularly also under very strong moonlight conditions, the GAPDs show no change in their properties or any indication for aging. This allows FACT to have a successful monitoring program of the brightest TeV blazars in the Northern hemisphere and several flare-alerts have been sent to the community. This proceeding summarizes the history and status of FACT as well as reporting the lessons learned about the usage of SiPM in a Cherenkov telescope from the construction and operation of FACT., SCOPUS: cp.p, info:eu-repo/semantics/published
Published: 2015

47. FACT-tools - Streamed real-time data analysis

Author: Brügge, Kai K.A., Ahnen, Max M.L., Balbo, Matteo, Bergmann, Matthias, Biland, Adrian, Bockermann, Christian, Bretz, Thomas, Buss, Jens, Dorner, Daniela, Einecke, Sabrina, Freiwald, J., Hempfling, Christina, Hildebrand, Dorothée, Hughes, Gareth, Lustermann, Werner, Mannheim, Karl, Meier, Katja, Morik, Katharina, Müller, Sebastian, Neise, Dominik, Neronov, Andrii, Nöthe, Max, Overkemping, A.K., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Temme, Fabian, Thaele, Julia, Toscano, Simona, Vogler, Patrick, Walter, Roland, Wilbert, A., Brügge, Kai K.A., Ahnen, Max M.L., Balbo, Matteo, Bergmann, Matthias, Biland, Adrian, Bockermann, Christian, Bretz, Thomas, Buss, Jens, Dorner, Daniela, Einecke, Sabrina, Freiwald, J., Hempfling, Christina, Hildebrand, Dorothée, Hughes, Gareth, Lustermann, Werner, Mannheim, Karl, Meier, Katja, Morik, Katharina, Müller, Sebastian, Neise, Dominik, Neronov, Andrii, Nöthe, Max, Overkemping, A.K., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Temme, Fabian, Thaele, Julia, Toscano, Simona, Vogler, Patrick, Walter, Roland, and Wilbert, A.
Abstract: The First G-APD Cherenkov telescope (FACT) is dedicated to monitor bright TeV blazars in the northern sky. The use of silicon photon detectors allows for a larger duty cycle, which results in a huge amount of collected data (800 GB/night). In order to satisfy its monitoring purpose, changes in the flux of the observed sources have to be registered without delay. This requires a data analysis that provides physical results at a rate that is comparable to the trigger rate of 80Hz. The recently developed data analysis software FACT-Tools aims to accomplish these requirements in real-time. It is implemented based on of the streams-framework, which was developed at Dortmund's collaborative research center for resource-constrained data analysis (SFB 876). Streams delivers an easy-to-use abstraction layer to design analysis processes by use of human readable XML files, which also make the analysis reproducible. Multi-source processes (e.g. simultaneous analyses of data from several telescopes) and multi-core processes (parallelization) are already included in the streams-framework. Therefore, Streams is an ideal framework for use in gamma-ray astronomy. The FACT-Tools are an extension library for the streams-framework with analysis methods for Cherenkov telescopes. The collection of methods is ranging from RAWdata handling and calibration up to image parameter extraction and Gamma-Proton classification. The latter is performed by an online application of a random forest classifier, which in turn, allows for an adaptation in other tasks e.g. image cleaning or online estimation of the energy spectrum. In this contribution we want to present the features of FACT-Tools and the streams-framework alongside with their performance measured on the data from the FACT Cherenkov telescope., SCOPUS: cp.p, info:eu-repo/semantics/published
Published: 2015

48. Data compression for the first G-APD Cherenkov Telescope

Author: Ahnen, Max M.L., Balbo, Matteo, Bergmann, Matthias, Biland, Adrian, Bretz, Thomas, Buss, Jens, Dorner, Daniela, Einecke, Sabrina, Freiwald, J., Hempfling, Christina, Hildebrand, Dorothée, Hughes, Gareth, Lustermann, Werner, Lyard, Etienne, Mannheim, Karl, Meier, Katja, Mueller, Sebastian Achim, Neise, Dominik, Neronov, Andrii, Overkemping, A.K., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Steinbring, T., Temme, Fabian, Thaele, Julia, Toscano, Simona, Vogler, Patrick, Walter, Roland, Wilbert, A., Ahnen, Max M.L., Balbo, Matteo, Bergmann, Matthias, Biland, Adrian, Bretz, Thomas, Buss, Jens, Dorner, Daniela, Einecke, Sabrina, Freiwald, J., Hempfling, Christina, Hildebrand, Dorothée, Hughes, Gareth, Lustermann, Werner, Lyard, Etienne, Mannheim, Karl, Meier, Katja, Mueller, Sebastian Achim, Neise, Dominik, Neronov, Andrii, Overkemping, A.K., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Steinbring, T., Temme, Fabian, Thaele, Julia, Toscano, Simona, Vogler, Patrick, Walter, Roland, and Wilbert, A.
Abstract: The FACT telescope on the Canaries island of La Palma is the first Imaging Atmospheric Cherenkov Telescope (IACT) to use solid state photomultipliers. It generates up to 2 TB of data per night which motivated us to investigate how to reduce the volume of data. Reducing the throughput enables us to efficiently acquire, store and process the observations data. This document presents the conclusions of this work, along with the implementation of the custom compression algorithm and I/O layer that is currently in use to operate the telescope., 0, SCOPUS: ar.j, info:eu-repo/semantics/published
Published: 2015

49. FACT - TeV flare alerts triggering multi-wavelength observations

Author: Dorner, Daniela, Ahnen, Max M.L., Balbo, Matteo, Bergmann, Matthias, Biland, Adrian, Bretzb, T., Brügge, Kai K.A., Buss, Jens, Einecke, Sabrina, Freiwald, J., Hempfling, Christina, Hildebrand, Dorothée, Hughes, Gareth, Lustermann, Werner, Mannheim, Karl, Meier, Katja, Müller, Sebastian, Neise, Dominik, Neronov, Andrii, Nöthe, Max, Overkemping, A.K., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Temme, Fabian, Thaele, Julia, Toscano, Simona, Vogler, Patrick, Walter, Roland, Wilbert, A., Dorner, Daniela, Ahnen, Max M.L., Balbo, Matteo, Bergmann, Matthias, Biland, Adrian, Bretzb, T., Brügge, Kai K.A., Buss, Jens, Einecke, Sabrina, Freiwald, J., Hempfling, Christina, Hildebrand, Dorothée, Hughes, Gareth, Lustermann, Werner, Mannheim, Karl, Meier, Katja, Müller, Sebastian, Neise, Dominik, Neronov, Andrii, Nöthe, Max, Overkemping, A.K., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Temme, Fabian, Thaele, Julia, Toscano, Simona, Vogler, Patrick, Walter, Roland, and Wilbert, A.
Abstract: Active galactic nuclei show variability on time scales ranging from minutes to decades. The radiation from these extreme objects spans many orders of magnitude along the whole electromagnetic spectrum. The spectral energy distribution shows two peaks, where for the subgroup of blazars the first peak is in the radio to X-ray regime, while the second peak is in the gamma-ray regime. Due to the extreme variability and the wide spectral range, simultaneous multi-wavelength observations are vital to understand the underlying physics. Furthermore, long-term monitoring is crucial to obtain an unbiased data sample. While for the measurements of the low-energy peak, many instruments are available, the data at TeV energies are sparse. The First G-APD Cherenkov Telescope (FACT) is a gamma-ray telescope dedicated to the long-term monitoring of bright TeV blazars. Operational since October 2011, it has collected more than three years of data from a dedicated sample of sources. The results of an automatic quick look analysis are publicly available on a website the same night. Based on this, other instruments are informed in case of a high flux state and target-of-opportunity observations are carried out. In the previous year, seven flare alerts have been sent to the community and several periods of strong variability have been observed for the blazars Mrk 421 and Mrk 501., SCOPUS: cp.p, info:eu-repo/semantics/published
Published: 2015

50. Using charged cosmic ray particles to monitor the data quality of FACT

Author: Hildebrand, Dorothée, Adam, Jan, Ahnen, Max Ludwig, Baack, Dominik, Balbo, Matteo, Biland, Adrian, Blank, Michael, Bretz, Thomas, Brügge, Kai, Buss, Jens, Dmytriiev, Anton, Dorner, Daniela, Einecke, Sabrina, Elsäesser, Dominik, Hempfling, Christina, Herbst, Tina, Kortmann, Lukas, Linhoff, Lena, Mahlke, Max, Mannheim, Karl, Müller, Sebastian, Neise, Dominik, Neronov, Andrii, Noethe, Maximilian, Oberkirch, J., Paravac, Aleksander, Pauss, Felicitas, Rhode, Wolfgang, Schleicher, B., Sliusar, Vitalii, Schulz, F., Shukla, Amit, Temme, Fabian, Thaele, Julia, and Walter, Roland
Subjects: Physics, business.industry, Astrophysics::High Energy Astrophysical Phenomena, Gamma ray, Astrophysics::Instrumentation and Methods for Astrophysics, Photodetector, Cosmic ray, IACT, Charged particle, law.invention, Telescope, Silicon photomultiplier, Optics, law, business, Cherenkov radiation
Abstract: Imaging Air Cherenkov Telescopes (IACT) measure the faint flashes of Cherenkov light emitted by air-showers that are produced when charged particles or gamma rays hit the atmosphere. Therefore, the atmosphere above the IACT is an integral part of the detector. Variations in the performance of the IACT itself, but also changes in the absorption and scattering of Cherenkov light due to clouds or dust affect the interpretation of measured signals. Therefore, information about the status of the full system is crucial to combine measurements from different time periods. The First G-APD Cherenkov Telescope (FACT) is using for the first time solid state photosensors (so-called G-APDs or SiPM) to measure the flashes of Cherenkov light. Based on the stability of these sensors, we showed in the past that it is possible to identify the existence of strong clouds or calima when measuring the intrinsically constant flux of cosmic ray particles at different trigger levels. This necessitated dedicated measurements, preventing normal data taking in parallel. We have now improved the method to use instead those cosmic ray events that are recorded during normal data taking as dominant background. By applying a fixed virtual trigger threshold in software, we measure the rate of charged cosmic ray particles. A deviation from the expected flux allows to identify data sets with reduced performance of the complete system in quasi real-time, without the need for any additional device. Applying the method to a data set when one of the 30 mirror tiles of FACT was missing, we show that a change of total yield of the Cherenkov light by few percent can be identified within few minutes of standard data taking. This nicely demonstrates that the hadron rate determined from standard data taking with FACT can be used for monitoring of the data quality., PoS: Proceedings of Science, 301, ISSN:1824-8039, ICRC2017 proceedings

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