Unravelling the complex behavior of Mrk421 with simultaneous X-ray and VHE observations during an extreme flaring activity in April 2013
2019 July 22
In April 2013, Mrk421 underwent unprecedented flaring activity, densely monitored during nine consecutive days at very-high-energy (VHE, E > 100 GeV) by MAGIC and VERITAS (with gamma-ray fluxes beyond 15 Crab Units above 800 GeV), in the hard X-rays by NuSTAR, in the soft X-rays by Swift-XRT, and by several optical and radio facilities. The high sensitivity of the instruments involved, together with the 43 (20) hours of strictly simultaneous observations in the VHE and X-ray energy bands with NuSTAR (Swift), make this dataset a unique opportunity for unveiling the highly energetic emission down to sub-hour timescales. In the present contribution, we report on the detected intranight variability, which could be decomposed into a fast (sub-hour) and slow (multi-hour) components that evolve differently across the various energy bands probed, showing a large degree of complexity in the relations between the emission at gamma-rays and that at X-rays. We will also discuss the consistency of the observed multi-band variability with theoretical scenarios where many blobs of magnetized plasma containing energetic particles are formed and accelerated in magnetic reconnection layers in the jet of the blazar.