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Fermi-LAT detection of renewed gamma-ray activity from the radio source GB6 J0713+5738

ATel #11056; R. Angioni (MPIfR-Bonn), S. Buson (NASA/GSFC), C. C. Cheung (NRL), R. Ojha (NASA/GSFC/UMBC), B. Carpenter (CUA/NASA/GSFC) on behalf of the Fermi-LAT collaboration
on 14 Dec 2017; 12:36 UT
Credential Certification: Sara Buson (sara.buson@gmail.com)

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

Referred to by ATel #: 11331, 11335

The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope, has observed enhanced gamma-ray emission from a source positionally consistent with the radio source GB6 J0713+5738, with coordinates R.A. = 108.268946 deg, Decl. = 57.636144 deg (J2000; Jackson et al. 2007 MNRAS, 376, 371), and no measured redshift. Fermi-LAT already reported a flare from a source positionally consistent with this in ATel #10149, but this source is not in any published LAT catalog and was not detected by AGILE or EGRET.

Preliminary analysis indicates that, following the flaring activity of 5 March 2017, reported in ATel #10149, the source went again into a high-flux state of similar brightness on 3 September 2017, with a peak daily averaged gamma-ray flux (E>100MeV) of (0.5+/-0.1) X 10^-6 photons cm^-2 s^-1 and a photon index of 2.1+/-0.2 (statistical uncertainty only). The source then went into a quiescent state, and had another, brighter flaring episode on 12 December 2017, reaching a peak daily averaged gamma-ray flux (E>100MeV) of (1.1+/-0.1) X 10^-6 photons cm^-2 s^-1, with a photon index of 1.8+/-0.1 (statistical uncertainty only). This is the highest gamma-ray daily flux ever recorded for this source, and it is worth noting that it coincides with a significant hardening of the observed spectrum with respect to the previous, lower-flux states, a behavior typically observed in flaring Flat-Spectrum Radio Quasars (FSRQs).

In ATel #10149, it was not possible to robustly associate the source to a unique counterpart, and therefore the gamma-ray source was indicated as Fermi J0713+5739. However, the source localization from the three flaring episodes consistently overlaps and suggests a likely association of this gamma-ray source with GB6 J0713+5738.

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. We encourage further multifrequency observations of this source. The Fermi-LAT contact people for this source are R. Angioni (angioni at mpifr-bonn.mpg.de) and B. Carpenter (carpbr01 at gmail.com).

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.