VHE gamma-ray spectral hint of two-zone emitting region in Mrk 501

Discussion timeslot (ZOOM-Meeting): 13. July 2021 - 18:00
ZOOM-Meeting URL: https://desy.zoom.us/j/98542982538
ZOOM-Meeting ID: 98542982538
ZOOM-Meeting Passcode: ICRC2021
Corresponding Session: https://icrc2021-venue.desy.de/channel/48-Modelling-AGN039s-spectral-energy-distribution-GAD-GAI-MM/77
Live-Stream URL: https://icrc2021-venue.desy.de/livestream/Discussion-04/5

Abstract:
Markarian 501 (Mrk 501) is one of the brightest very high energy (VHE, E larger 100 GeV) gamma-ray blazars. It is located in our neighborhood, at redshift zu2004=u20040.034. During a multi-wavelength campaign in July 2014, Mrk 501 displayed the highest X-ray activity observed by the Neil Gehrels Swift X-ray telescope (XRT) since its launch. The X-ray spectra displayed during this flaring episode were very hard, and showed variability on nightly timescales. On 2014 July 19, in coincidence with the peak of the X-ray activity, a hint of a narrow feature at ~3 TeV was observed with the MAGIC telescopes. Such feature makes the VHE spectrum inconsistent with the classical analytic functions used to describe the measured VHE spectra (power law, log-parabola, and log-parabola with exponential cutoff) at more than 3σ. A double-log-parabola fit is preferred w.r.t. a single one at more than 4σ confidence level. Three different scenarios that could produce such an effect are discussed: (a) a pileup in the electron energy distribution, (b) a two-zone Synchrotron Self-Compton (SSC) emission model, and (c) a pair cascade model. In this contribution we will present the observational details and a general overview of the possible physical mechanisms of this unprecedented observation.'

Authors: Josefa Becerra González | David Paneque | Christoph Wendel | Koji Noda | Kazuma Ishio | Fabrizio Tavecchio | Karl Mannheim | Andrea Tramacere
Collaboration: MAGICFermi-LAT

Indico-ID: 79
Proceeding URL: https://pos.sissa.it/395/774