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

ATel #7633; Sara Cutini (ASDC/INFN), on behalf of the Fermi-LAT collaboration
on 15 Jun 2015; 17:04 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@asdc.asi.it)

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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.: 194.0465271 deg, Dec: -5.7893119 deg (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) and is one of the four FSRQs known to be VHE gamma-ray emitters.

Preliminary analysis indicates that the source was in a high state on June 14 with a daily gamma-ray flux (E>100MeV) of (16.3+1.0) x 10^-6 photons cm^-2 s^-1 more than a factor of 40 greater than the average value reported in the 3FGL. In particular the last six hour run showed flux around (19.6+/-2.5) 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 about 2.2+/-0.1 and 2.4+/-0.1, respectively. This strong flare was detected also by AGILE, but with a lower flux, reported in ATel#7631.

This outburst corresponds to the highest daily gamma-ray flux ever observed by the LAT from this blazar since the start of the Fermi mission, after the last flaring activity reported on December 2013 (ATel#5680) and April 2014 (ATel#6036). At 16:31 UT on June 15, Fermi started a 300 ks target of opportunity observation to increase LAT exposure on 3C 279. 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 (mahaya@icrr.u-tokyo.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.