@article{RoelofsBlackburnLindahletal.2023,
  author    = {Roelofs, Freek and Blackburn, Lindy and Lindahl, Greg and Doeleman, Sheperd S. and Johnson, Michael D. and Arras, Philipp and Chatterjee, Koushik and Emami, Razieh and Fromm, Christian and Fuentes, Antonio and Knollm{\"u}ller, Jakob and Kosogorov, Nikita and M{\"u}ller, Hendrik and Patel, Nimesh and Raymond, Alexander and Tiede, Paul and Traianou, Efthalia and Vega, Justin},
  title     = {The ngEHT analysis challenges},
  series = {Galaxies},
  volume    = {11},
  journal   = {Galaxies},
  number    = {1},
  issn      = {2075-4434},
  doi       = {10.3390/galaxies11010012},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-304976},
  year      = {2023},
  abstract  = {The next-generation Event Horizon Telescope (ngEHT) will be a significant enhancement of the Event Horizon Telescope (EHT) array, with ∼10 new antennas and instrumental upgrades of existing antennas. The increased uv-coverage, sensitivity, and frequency coverage allow a wide range of new science opportunities to be explored. The ngEHT Analysis Challenges have been launched to inform the development of the ngEHT array design, science objectives, and analysis pathways. For each challenge, synthetic EHT and ngEHT datasets are generated from theoretical source models and released to the challenge participants, who analyze the datasets using image reconstruction and other methods. The submitted analysis results are evaluated with quantitative metrics. In this work, we report on the first two ngEHT Analysis Challenges. These have focused on static and dynamical models of M87* and Sgr A* and shown that high-quality movies of the extended jet structure of M87* and near-horizon hourly timescale variability of Sgr A* can be reconstructed by the reference ngEHT array in realistic observing conditions using current analysis algorithms. We identify areas where there is still room for improvement of these algorithms and analysis strategies. Other science cases and arrays will be explored in future challenges.},
  language  = {en}
}
@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}
}