Fermi-LAT detection of the highest-level gamma-ray outburst from the high-redshift blazar S5 0836+71 (4C +71.07)

ATel #7870; Stefano Ciprini (ASDC Rome & INFN Perugia, Italy), on behalf of the Fermi Large Area Telescope Collaboration.
on 3 Aug 2015; 18:25 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 flaring gamma rays from a source positionally consistent with the flat spectrum radio quasar S5 0836+71 (also known as 4C +71.07, 1ES 0836+710, and 3FGL J0841.4+7053), with radio coordinates, (J2000.0), R.A.: 130.35152 deg, Dec.: 70.89505 deg. (Johnston et al. 1995, AJ, 110, 880). This blazar has a redshift z=2.218 (McIntosh et al. 1999, ApJ, 514, 40).

Preliminary analysis indicates that on 2 August 2015 this distant FSRQ was in the highest-flux state observed by the LAT since the launch of Fermi, with a daily gamma-ray flux (E>100MeV) of (5.3+/-0.4) X 10^-6 photons cm^-2 s^-1, and a peak 6-hour (12:00-18:00 UT) interval gamma-ray flux of (6.5+/-0.7) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 65 times greater than the average flux reported in the third Fermi-LAT source catalog, 3FGL (Acero et al. 2015, ApJS 218, 23). The corresponding spectral photon indices (E>100MeV) of respectively (2.5+/-0.1) and (2.7+/-0.2) are roughly in line with the soft average index of 2.703+/-0.029 in the 3FGL catalog.

This distant gamma-ray MeV-peaked source was previously detected by Swift BAT, NuSTAR, INTEGRAL, COMPTEL and EGRET, (Cusumano et al. 2010, A&A, 524, 64; Tagliaferri et al. 2015, ApJ, 807, 167; Pian et al. 2005, A&A, 429, 427; Collmar 2006, ASP Conf. Ser. 350, 120; Hartman et al. 1999, ApJS, 123, 79), and this is the third time that Fermi is announcing gamma-ray flaring activity from this FSRQ through an ATel, after April and December 2011 (ATel#3260 and ATel#3831).

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/S5_0836p71).

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 persons are K. Sokolovsky (ksokolov@mpifr-bonn.mpg.de) and D.J. Thompson (David.J.Thompson@nasa.gov).

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.