TY - JOUR A1 - Temme, Fabian A1 - Adam, Jan A1 - Ahnen, Max L. A1 - Baack, Dominik A1 - Balbo, Matteo A1 - Bergmann, Matthias A1 - Biland, Adrian A1 - Blank, Michael A1 - Bretz, Thomas A1 - Brügge, Kai A. A1 - Buss, Jens A1 - Dmytriiev, Anton A1 - Dorner, Daniela A1 - Einecke, Sabrina A1 - Hempfling, Christina A1 - Hildebrand, Dorothee A1 - Hughes, Gareth A1 - Linhoff, Lena A1 - Mannheim, Karl A1 - Müller, Sebastian A1 - Neise, Dominik A1 - Neronov, Andrii A1 - Nöthe, Max A1 - Paravac, Aleksander A1 - Pauss, Felicitas A1 - Rhode, Wolfgang A1 - Shukla, Amit A1 - Thaele, Julia A1 - Walter, Roland T1 - Long-Term monitoring of bright blazars in the multi-GeV to TeV range with FACT JF - Galaxies N2 - 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. KW - Imaging Air Cherenkov Telescope KW - First G-APD Cherenkov Telescope KW - very high energy gamma rays KW - long-term monitoring KW - silicon photo multiplier Y1 - 2017 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-198088 SN - 2075-4434 VL - 5 IS - 1 PB - MDPI ER - TY - JOUR A1 - Romoli, Carlo A1 - Chakraborty, Nachiketa A1 - Dorner, Daniela A1 - Taylor, Andrew A1 - Blank, Michael T1 - Flux Distribution of Gamma-Ray Emission in Blazars: The Example of Mrk 501 JF - Galaxies N2 - 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 KW - gamma rays KW - very high energy KW - active galactic nuclei KW - Markarian 501 KW - monitoring KW - flux distributions Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-197580 SN - 2075-4434 VL - 6 IS - 4 ER - TY - JOUR A1 - Schleicher, Bernd A1 - Arbet-Engels, Axel A1 - Baack, Dominik A1 - Balbo, Matteo A1 - Biland, Adrian A1 - Blank, Michael A1 - Bretz, Thomas A1 - Bruegge, Kai A1 - Bulinski, Michael A1 - Buss, Jens A1 - Doerr, Manuel A1 - Dorner, Daniela A1 - Elsaesser, Dominik A1 - Grischagin, Sergej A1 - Hildebrand, Dorothee A1 - Linhoff, Lena A1 - Mannheim, Karl A1 - Mueller, Sebastian Achim A1 - Neise, Dominik A1 - Neronov, Andrii A1 - Noethe, Maximilian A1 - Paravac, Aleksander A1 - Rhode, Wolfgang A1 - Schulz, Florian A1 - Sedlaczek, Kevin A1 - Shukla, Amit A1 - Sliusar, Vitalii A1 - Willert, Elan A1 - Walter, Roland T1 - Fractional Variability—A Tool to Study Blazar Variability JF - Galaxies N2 - 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. KW - blazars KW - variability KW - fractional variability KW - active galactic nuclei Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-197348 SN - 2075-4434 VL - 7 IS - 2 ER -