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Fermi LAT observation of ongoing GeV activity from spectrally hard blazar GB6 B1310+4844 (GB1 1310+487)

ATel #2316; E. Hays (NASA/GSFC), L. Escande (CNRS/IN2P3 Bordeaux) on behalf of the Fermi Large Area Telescope Collaboration
on 28 Nov 2009; 00:29 UT
Credential Certification: Elizabeth Hays (elizabeth.a.hays@nasa.gov)

Subjects: Gamma Ray, >GeV, Transient

Referred to by ATel #: 2320, 5202

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, recently reported an increasing gamma-ray flux from a source positionally consistent with the flat spectrum radio quasar (FSRQ) GB6 B1310+4844 (also known as GB1 1310+487) in ATEL #2306. The gamma-ray high state has been confirmed by AGILE (ATEL #2310) and infrared flaring has also been observed (ATEL #2311).

The LAT source has been active in each of the last nine days and shows significant variability. Preliminary analysis for November 26, 2009, finds a gamma-ray flux (photon energy E>100MeV) of (1.2 +/- 0.2) x 10^-6 photons cm^-2 s^-1 and a very hard photon index of 1.8 +/- 0.1 (errors are statistical only). For comparison, the average photon index during the first 11 months of LAT observations (August 4, 2008, through July 4, 2009) is 2.3 +/- 0.1.

The gamma-ray photon index during this high state is one of the smallest seen in LAT-detected FSRQs. In the LAT bright AGN sample (Abdo et al., 2009, ApJ, 700, 597), all of the average photon indices for FSRQs were found to be greater than 2.0. Because of the strong gamma-ray variability and spectral hardness, multiwavelength observations, particularly optical monitoring, are strongly encouraged. Additional updates may be found on the Fermi Gamma-Ray Sky blog

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 strongly encourage multiwavelength observations. For this source the Fermi LAT contact person is K. Sokolovsky (ksokolov[at]mpifr-bonn.mpg.de).