Jul 12 – 23, 2021
Europe/Berlin timezone

Multi-wavelength study of Mrk 421 during a TeV outburst

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


Talk GAI | Gamma Ray Indirect Discussion


Andrea Gokus


The blazar Mrk 421 shows frequent, short outbursts 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 began a program to monitor the object with the FACT (TeV energies) and the Neil Gehrels Swift Observatory (X-rays). In case of flaring activity being detected, additional observations in the X-ray band can be triggered from our approved programs (XMM-Newton, INTEGRAL).
On June 9 2019, Mrk 421 showed a TeV outburst reaching a flux level (> 0.8 TeV) of more than two times the flux of the Crab Nebula at TeV energies.
We triggered all instruments involved in our campaign and acquired simultaneous MWL data. 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 dataset is complemented by continous monitoring by the Fermi satellite in the MeV-GeV range and pointed radio observations by Effelsberg at GHz frequencies. The dense X-ray coverage during the TeV flare revealed significant spectral hardening, short-time variability and a shift of the lower-hump peak in the spectral energy distribution of Mrk 421.
We present the results of the timing analysis, as well as the multi-wavelength analysis, and their implications on modeling the spectral energy distribution of blazars.


AGN; Blazar; multi-wavelength; FACT; Mrk 421; TeV outburst; X-rays; gamma-rays; timing analysis; SED modelling

Collaboration Ferrmi-LAT
other Collaboration FACT
Subcategory Experimental Results

Primary authors

Andrea Gokus Matthias Kadler Michael Kreter (North-West University) Felicia Krauss (GRAPPA & API, UvA) Daniela Dorner (Universität Würzburg) Dr Tobias Beuchert Thomas Bretz (RWTH Aachen University) Dr Thomas Dauser Dominik Elsaesser (TU Dortmund) Dorit Glawion (ECAP, FAU Erlangen-Nürnberg) Alex Kraus Dr Annika Kreikenbohm Ms Ingo Kreykenbohm Marcus Langejahn Katharina Leiter Prof. Karl Mannheim (Universität Würzburg) Joern Wilms (ECAP & Remeis-Observatory, University of Erlangen-Nuremberg) and on behalf of the FACT collaboration

Presentation materials