Jul 12 – 23, 2021
Europe/Berlin timezone

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

Jul 13, 2021, 6:00 PM
1h 30m


Talk GAI | Gamma Ray Indirect Discussion


Josefa Becerra González (Insituto de Astrofísica de Canarias & Universidad de La Laguna)


Markarian 501 (Mrk 501) is one of the brightest very high energy (VHE, E> 100 GeV) gamma-ray blazars. It is located in our neighborhood, at redshift z = 0.034. 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.


galaxies: active / BL Lacertae objects: individual: Mrk 501 / gamma rays: galaxies / X-rays: galaxies

other Collaboration Fermi-LAT
Subcategory Experimental Results
Collaboration MAGIC

Primary authors

Josefa Becerra González (Insituto de Astrofísica de Canarias & Universidad de La Laguna) David Paneque (Max Planck Institute for Physics) Mr Christoph Wendel (Universität Würzburg) Koji Noda (Institute for Cosmic Ray Research, The University of Tokyo) Mr Kazuma Ishio (MPI) Fabrizio Tavecchio (INAF-OAB) Prof. Karl Mannheim (Universität Würzburg) Dr Andrea Tramacere

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