Very hard gamma-ray emission from a flare of Mrk 501

Abstract

We investigate the peculiar properties of a large TeV gamma-ray flare from Mrk~501 detected during the 2009 multiwavelength campaign. We identify the counterpart of the flare in the Fermi/LAT telescope data and study its spectral and timing characteristics. A strong order-of-magnitude increase of the very-high-energy gamma-ray flux during the flare was not accompanied by an increase in the X-ray flux, so that the flare was one of the "orphan"-type TeV flares observed in BL Lacs. The flare lasted about 1 month at energies above 10 GeV. The flaring source spectrum in the 10-200 GeV range was very hard, with a photon index 1.1+/-0.2, harder than that observed in any other blazar in the gamma-ray band. No simultaneous flaring activity was detected below 10 GeV. Different variability properties of the emission below and above 10 GeV indicate the existence of two separate components in the spectrum. We investigate possible explanations of the very hard flaring component. We consider, among others, the possibility that the flare is produced by an electromagnetic cascade initiated by very-high-energy gamma-rays in the intergalactic medium. Within such an interpretation, peculiar spectral and temporal characteristics of the flare could be explained if the magnetic field in the intergalactic medium is of the order of 1e-17 - 1e-16 G.

4 pages 3 figures, accepted for publication in A&A

References in corpus (19)

• Evidence for strong extragalactic magnetic fields from Fermi observations of TeV blazars
• The Spectrum of the Isotropic Diffuse Gamma-Ray Emission Derived From First-Year Fermi Large Area Telescope Data
• EGMF Constraints from Simultaneous GeV-TeV Observations of Blazars
• Synchrotron Self-Compton Analysis of TeV X-ray Selected BL Lacertae Objects
• New constraints on the Mid-IR EBL from the HESS discovery of VHE gamma rays from 1ES 0229+200
• Insights Into the High-Energy Gamma-ray Emission of Markarian 501 from Extensive Multifrequency Observations in the Fermi Era
• Time Delay of Cascade Radiation for TeV Blazars and the Measurement of the Intergalactic Magnetic Field
• Production of TeV gamma-radiation in the vicinity of the supermassive black hole in the giant radiogalaxy M87
• Fermi acceleration in astrophysical jets
• Formation of hard VHE gamma-ray spectra of blazars due to internal photon-photon absorption
• Stochastic particle acceleration and synchrotron self--Compton radiation in TeV blazars
• Hard TeV spectra of blazars and the constraints to the IR intergalactic background
• Discovery of VHE gamma-rays from the distant BL Lac 1ES 0347-121
• The Hard VHE Gamma-ray Emission in High-Redshift TeV Blazars: Comptonization of Cosmic Microwave Background Radiation in an Extended Jet?
• Lower Bounds on Intergalactic Magnetic Fields from Simultaneously Observed GeV-TeV Light Curves of the Blazar Mrk 501
• A method of measurement of extragalactic magnetic fields by TeV gamma ray telescopes
• Modeling the hard TeV spectra of blazars 1ES 0229+200 and 3C 66A with an internal absorption scenario
• Measuring parameters of AGN central engines with very high energy gamma-ray flares
• A Structured Leptonic Jet Model of the "Orphan" TeV Gamma-Ray Flares in TeV Blazars

Cited by in corpus (35)

• Cosmological Magnetic Fields: Their Generation, Evolution and Observation
• Blazars as Ultra-High-Energy Cosmic-Ray Sources: Implications for TeV Gamma-Ray Observations
• Fermi/LAT observations of 1ES 0229+200: implications for extragalactic magnetic fields and background light
• Formation of hard very-high energy spectra of blazars in leptonic models
• The Steady Growth of the High-Energy Spectral Cutoff in Relativistic Magnetic Reconnection
• The Gamma-Ray Window to Intergalactic Magnetism
• Multiband variability studies and novel broadband SED modeling of Mrk 501 in 2009
• X-ray Intraday Variability of Five TeV Blazars with NuSTAR
• ASTRI Mini-Array Core Science at the Observatorio del Teide
• Particle acceleration in the vacuum gaps in black hole magnetospheres
• On the magnetic fields in voids
• On the detectability of Lorentz invariance violation through anomalous multi-TeV $\gamma$-ray spectra of blazars
• Study of the variable broadband emission of Markarian 501 during the most extreme Swift X-ray activity
• Radio Galaxies at VHE energies
• Discovery of TeV gamma-ray emission from PKS 0447-439 and derivation of an upper limit on its redshift
• Evidence for the Secondary Emission as the Origin of Hard Spectra in TeV Blazars
• Multi-frequency, Multi-Epoch Study of Mrk 501: Hints for a two-component nature of the emission
• Bethe-Heitler cascades as a plausible origin of hard spectra in distant TeV blazars
• The hadronic origin of hard gamma-ray spectrum from blazar 1ES 1101-232
• Electromagnetic cascade masquerade: a way to mimic $\gamma$--axion-like particle mixing effects in blazar spectra
• Multi-color optical monitoring of Mrk 501 from 2010 to 2015
• Verification of the diffusive shock acceleration in Mrk 501
• Search for intra-day optical variability in Mrk 501
• Quasi-simultaneous Spectroscopic and Multi-band Photometric Observations of Blazar S5 0716+714 during 2018-2019
• On conservative models of "the pair-production anomaly" in blazar spectra at Very High Energies
• On the narrow spectral feature at $\sim$3 TeV in the MAGIC spectrum of Mrk 501
• Search for ultra high energy cosmic rays from radiogalaxy Virgo A
• The nature of the intrinsic spectra from the VHE emission of H 2356-309 and 1ES 1101-232
• $R$-band host galaxy contamination of TeV $\gamma$-ray blazar Mrk 501: effects of the aperture size and seeing
• Six-year Optical Monitoring of BL Lacertae Object 1ES 0806+52.4
• Rapid variability at very high energies in Mrk 501
• Properties and Possible Physical Origins of $\gamma$-ray Emission in Extreme Synchrotron Blazars
• Testing models of extragalactic $\gamma$-ray propagation using observations of extreme blazars in GeV and TeV energy ranges
• Cascade Model of an Anomaly in Blazar Spectra at Very High Energy
• The VHE anomaly in blazar spectra and related phenomena