Jul 12 – 23, 2021
Europe/Berlin timezone

Relentless multi-wavelength variability of Markarian 421 and Markarian 501

Jul 15, 2021, 12:00 PM
1h 30m


Talk GAI | Gamma Ray Indirect Discussion


Sliusar Vitalii (Université de Genève)


The high-synchrotron-peaked blazars Markarian 421 and Markarian 501 are close bright and well-studied active galactic nuclei, which feature persistent GeV and TeV emission. FACT and Fermi-LAT have been monitoring these two sources providing the densest long-term dataset of unbiased gamma ray observations. Light curves in the TeV and GeV energy bands, spanning over a five-year period, were used to study the multi-wavelength emission. To characterize the variability and derive constraints on the emission mechanism model parameters, the dataset was augmented with contemporaneous multi-wavelength observations from radio to the X-rays. The blazars were found in various activity states, particularly a quiescent state of Markarian 501 after August, 2016. We correlate the light curves from radio to gamma rays, identify individual flares and look for inter-band connections, which are expected from the shock propagations within the jet. The fractional variability for both blazars shows a two-bump structure with the highest variability in the X-ray and TeV bands. The lag between X-ray and TeV light curves in Markarian 421 was found to be close to zero, supporting the SSC emission scenario. The timing between both TeV and X-ray flares in Markarian 421 is consistent with periods expected in the case of Lense–Thirring precession of the accretion disc. The variability of Markarian 501 on the long-term scale is also consistent with SSC, with a sub-day lag between X-ray and TeV variability.


AGN, Mrk 421, Mrk 501, blazars, FACT, IACT

other Collaboration FACT
Collaboration other (fill field below)
Subcategory Experimental Results

Primary author

Sliusar Vitalii (Université de Genève)


Axel Arbet-Engels (ETH Zürich) Dominik Baack (TU Dortmund) Matteo Balbo (ISDC, Univeristé de Genève) Noah Biederbeck (TU Dortmund) Adrian Biland (ETH Zurich) Thomas Bretz (RWTH Aachen University) Jens Buss (Lehrstuhl für Astroteilchenphysik TU Dortmund) Daniela Dorner (Universität Würzburg) Laura Eisenberger (University of Wurzburg) Dominik Elsaesser (TU Dortmund) Dorothee Hildebrand (ETH Zurich) Roman Iotov (Julius Maximilians University Wuerzburg, FACT) Prof. Karl Mannheim (Universität Würzburg) Dominik Neise (ETH Zurich) Maximilian Noethe (TU Dortmund) Aleksander Paravac (University of Wurzburg) Prof. Wolfgang Rhode Bernd Schleicher (University of Wurzburg) Dr Roland Walter (University of Geneve)

Presentation materials