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Fermi LAT detection of strong GeV activity from the blazar 3C 279

ATel #11189; Pfesesani van Zyl (Hartebeesthoek Radio Astronomy Observatory) and Roopesh Ojha (NASA/GSFC/UMBC) on behalf of the Fermi Large Area Telescope Collaboration
on 17 Jan 2018; 16:44 UT
Credential Certification: Roopesh Ojha (Roopesh.Ojha@gmail.com)

Subjects: Gamma Ray, >GeV, AGN, Blazar, Quasar

Referred to by ATel #: 11190, 11196, 11200, 11202, 11239, 11246, 11464, 11542

The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has observed an intense gamma-ray flare from a source positionally consistent with the flat spectrum radio quasar 3C 279, also known as 3FGL J1256.1-0547 (Acero et al. 2015, ApJS, 218, 23), with radio coordinates R.A.: 12h56m11.1665s, Dec: -05d47m21.523s (J2000.0; Johnston et al. 1995, AJ, 110, 880). This blazar has a redshift of z=0.5362 (Marziani et al. 1996, ApJS, 104, 37). It is one of only seven FSRQs known to be VHE gamma-ray emitters.

Preliminary analysis indicates that the source flux has been increasing in the past few days reaching a high state on January 15 with an average gamma-ray flux (E>100MeV) of (8.4+/-0.5) x 10^-6 photons cm^-2 s^-1, a factor of almost 20 greater than the average value reported in the 3FGL. In particular during 18:00-24:00 UTC the average flux was (11.6+/-1.5) x 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). The corresponding average gamma-ray spectrum had a photon index (E>100 MeV) of 2.2+/-0.1.

This flare represents the highest daily gamma-ray flux detected by the LAT from this blazar since the flare during June 2015 (ATel #7633). This source is one of the "LAT Monitored Sources" and consequently a preliminary estimation of the daily gamma-ray flux observed by Fermi LAT is publicly available (http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/3C_279).

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the ongoing activity of this source, we encourage multiwavelength observations. For this source the Fermi LAT contact people are Greg Madejski (madejski@slac.stanford.edu) and Masaaki Hayashida (masaaki.hayashida@hepburn.s.chiba-u.ac.jp).

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.