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MAGIC and VERITAS detect an unprecedented flaring activity from Mrk 421 in very high energy gamma-rays

ATel #4976; Juan Cortina (IFAE Barcelona) and Jamie Holder (University of Delaware) for the MAGIC and VERITAS collaborations
on 13 Apr 2013; 20:22 UT
Credential Certification: Juan Cortina (cortina@ifae.es)

Subjects: Optical, X-ray, Gamma Ray, TeV, VHE, Request for Observations, AGN, Blazar, Transient

Referred to by ATel #: 4977, 4978, 4982, 4983, 5021, 5107

The MAGIC and VERITAS telescopes have observed an unprecedented flaring activity in the Very High Energy (VHE; >100 GeV) gamma-ray flux from Markarian 421 (RA= 11 04 27.31, Dec=38 12 31.8, J2000.0). These observations were initially performed within a pre-planned extensive multi-instrument campaign that started in December 2012, and intensified in the last days because of the extreme VHE activity observed. Mrk421 is a high-synchrotron-peaked BL Lac located at redshift 0.031, which was first reported as a VHE emitter in 1992 (Punch et al 1992, Nature 358, 477). The typical VHE flux of this source is about 0.5 times the flux from the Crab Nebula (Crab Units, c.u.), as reported in Abdo et al 2011, ApJ 736, 131 and references therein, and the highest level of VHE activity ever measured for this source was about 10 c.u. (Gaidos et al. 1996, Nature 383, 319, and also Fortson et al. 2012, American Institute of Physics Conference Series, 1505, 514).

The preliminary analysis of the VHE data taken with MAGIC and VERITAS during the last three consecutive nights (from 2013/04/11 to 2013/04/13) indicate a persistently high flux of about 5 c.u. above 300 GeV, but very variable and with maxima reaching beyond 11 c.u. This implies an increase by a factor of more than 20 with respect to the typical (not lowest) VHE flux from this source above 300 GeV, and represent the highest VHE activity recorded for this object to date.

Besides MAGIC and VERITAS, the campaign also includes dedicated observations at radio and optical wavelengths with various instruments, and X-rays with Swift and NuSTAR. The source has been found to be also very high at optical and X-ray (see ATel #4974).

The campaign on Mrk421 will continue until June 2013, with a very intense broadband coverage (including MAGIC and VERITAS) during the coming days until April 17th. Multiwavelength observations are encouraged. The MAGIC and VERITAS contact persons for this campaign are David Paneque (dpaneque@mppmu.mpg.de) and Wystan Benbow (wbenbow@cfa.harvard.edu).