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Fermi LAT detection of a GeV flare from the FSRQ 3C 279

ATel #5680; Buson S. (University & INFN of Padova) on behalf of the Fermi Large Area Telescope Collaboration
on 21 Dec 2013; 17:54 UT
Credential Certification: Sara Buson (buson@pd.infn.it)

Subjects: Gamma Ray, >GeV, TeV, VHE, Request for Observations, AGN, Blazar

Referred to by ATel #: 5682, 6036, 7633

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed an increasing gamma-ray flux from a source positionally consistent with the blazar 3C279 (RA: 194.0465271, Dec: -5.7893119 , Johnston et al.1995, AJ, 110, 880, J2000). This source is classified as a flat spectrum radio quasar (FSRQ) at redshift of 0.536 (Marziani et al. ApJS, 1996, 104, 37) and is one of the three FSRQs known to be VHE gamma-ray emitters.

Preliminary analysis indicates that on 2013 December 20 the daily averaged flux (E>100MeV) was (6 +/- 1) x 10^-6 photons cm^-2 s^-1, more than a factor of 10 greater than reported in the second Fermi LAT catalog (2FGL J1256.1-0547, Nolan et al. 2012, ApJS 199, 31). This intense gamma-ray flare corresponds to the highest flux observed by the LAT since the start of the Fermi mission and follows an increasing trend recorded during the course of this month. Beside this, the source showed a particularly hard gamma-ray spectrum with a daily photon index of 1.80 +/- 0.06 (errors are statistical only) on 2013 December 20. Average photon indices for LAT-detected FSRQs are typically greater than 2.0.

The Fermi LAT contact people for this source are Greg Madejski (madejski@slac.stanford.edu) and Masaaki Hayashida (mahaya@slac.stanford.edu). In consideration of the ongoing activity of this source we strongly encourage multiwavelength observations.

The Fermi LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.