@article{SchleicherArbetEngelsBaacketal.2019,
  author    = {Schleicher, Bernd and Arbet-Engels, Axel and Baack, Dominik and Balbo, Matteo and Biland, Adrian and Blank, Michael and Bretz, Thomas and Bruegge, Kai and Bulinski, Michael and Buss, Jens and Doerr, Manuel and Dorner, Daniela and Elsaesser, Dominik and Grischagin, Sergej and Hildebrand, Dorothee and Linhoff, Lena and Mannheim, Karl and Mueller, Sebastian Achim and Neise, Dominik and Neronov, Andrii and Noethe, Maximilian and Paravac, Aleksander and Rhode, Wolfgang and Schulz, Florian and Sedlaczek, Kevin and Shukla, Amit and Sliusar, Vitalii and Willert, Elan and Walter, Roland},
  title     = {Fractional Variability—A Tool to Study Blazar Variability},
  series = {Galaxies},
  volume    = {7},
  journal   = {Galaxies},
  number    = {2},
  issn      = {2075-4434},
  doi       = {10.3390/galaxies7020062},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-197348},
  year      = {2019},
  abstract  = {Active Galactic Nuclei emit radiation over the whole electromagnetic spectrum up to TeV energies. Blazars are one subtype with their jets pointing towards the observer. One of their typical features is extreme variability on timescales, from minutes to years. The fractional variability is an often used parameter for investigating the degree of variability of a light curve. Different detection methods and sensitivities of the instruments result in differently binned data and light curves with gaps. As they can influence the physics interpretation of the broadband variability, the effects of these differences on the fractional variability need to be studied. In this paper, we study the systematic effects of completeness in time coverage and the sampling rate. Using public data from instruments monitoring blazars in various energy ranges, we study the variability of the bright TeV blazars Mrk 421 and Mrk 501 over the electromagnetic spectrum, taking into account the systematic effects, and compare our findings with previous results. Especially in the TeV range, the fractional variability is higher than in previous studies, which can be explained by the much longer (seven years compared to few weeks) and more complete data sample.},
  language  = {en}
}
@article{RomoliChakrabortyDorneretal.2018,
  author    = {Romoli, Carlo and Chakraborty, Nachiketa and Dorner, Daniela and Taylor, Andrew and Blank, Michael},
  title     = {Flux Distribution of Gamma-Ray Emission in Blazars: The Example of Mrk 501},
  series = {Galaxies},
  volume    = {6},
  journal   = {Galaxies},
  number    = {4},
  organization    = {FACT and H.E.S.S. Collaborations},
  issn      = {2075-4434},
  doi       = {10.3390/galaxies6040135},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-197580},
  year      = {2018},
  abstract  = {Flux distribution is an important tool to understand the variability processes in activegalactic nuclei. We now have available a great deal of observational evidences pointing towards thepresence of log-normal components in the high energy light curves, and different models have beenproposed to explain these data. Here, we collect some of the recent developments on this topic usingthe well-known blazar Mrk 501 as example of complex and interesting aspects coming from its fluxdistribution in different energy ranges and at different timescales. The observational data we refer toare those collected in a complementary manner by Fermi-LAT over multiple years, and by the FirstG-APD Cherenkov Telescope (FACT) telescope and the H.E.S.S. array in correspondence of the brightflare of June 2014},
  language  = {en}
}
@article{TemmeAdamAhnenetal.2017,
  author    = {Temme, Fabian and Adam, Jan and Ahnen, Max L. and Baack, Dominik and Balbo, Matteo and Bergmann, Matthias and Biland, Adrian and Blank, Michael and Bretz, Thomas and Br{\"u}gge, Kai A. and Buss, Jens and Dmytriiev, Anton and Dorner, Daniela and Einecke, Sabrina and Hempfling, Christina and Hildebrand, Dorothee and Hughes, Gareth and Linhoff, Lena and Mannheim, Karl and M{\"u}ller, Sebastian and Neise, Dominik and Neronov, Andrii and N{\"o}the, Max and Paravac, Aleksander and Pauss, Felicitas and Rhode, Wolfgang and Shukla, Amit and Thaele, Julia and Walter, Roland},
  title     = {Long-Term monitoring of bright blazars in the multi-GeV to TeV range with FACT},
  series = {Galaxies},
  volume    = {5},
  journal   = {Galaxies},
  number    = {1},
  publisher = {MDPI},
  issn      = {2075-4434},
  doi       = {10.3390/galaxies5010018},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-198088},
  pages     = {18},
  year      = {2017},
  abstract  = {Blazars like Markarian 421 or Markarian 501 are active galactic nuclei (AGN), with their jets orientated towards the observer. They are among the brightest objects in the very high energy (VHE) gamma ray regime (>100 GeV). Their emitted gamma-ray fluxes are extremely variable, with changing activity levels on timescales between minutes, months, and even years. Several questions are part of the current research, such as the question of the emission regions or the engine of the AGN and the particle acceleration. A dedicated longterm monitoring program is necessary to investigate the properties of blazars in detail. A densely sampled and unbiased light curve allows for observation of both high and low states of the sources, and the combination with multi-wavelength observation could contribute to the answer of several questions mentioned above. FACT (First G-APD Cherenkov Telescope) is the first operational telescope using silicon photomultiplier (SiPM, also known as Geigermode—Avalanche Photo Diode, G-APD) as photon detectors. SiPM have a very homogenous and stable longterm performance, and allow operation even during full moon without any filter, leading to a maximal duty cycle for an Imaging Air Cherenkov Telescope (IACT). Hence, FACT is an ideal device for such a longterm monitoring of bright blazars. A small set of sources (e.g., Markarian 421, Markarian 501, 1ES 1959+650, and 1ES 2344+51.4) is currently being monitored. In this contribution, the FACT telescope and the concept of longterm monitoring of bright blazars will be introduced. The results of the monitoring program will be shown, and the advantages of densely sampled and unbiased light curves will be discussed.},
  language  = {en}
}