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Fermi LAT detection of a GeV flare from GB6 B1310+4844

ATEL # 2306; K. V. Sokolovsky (MPIfR/ASC Lebedev), S. E. Healey (Stanford/KIPAC), F. Schinzel (MPIfR); on behalf of the Fermi Large Area Telescope Collaboration, and Y. Y. Kovalev (ASC Lebedev/MPIfR)
on 21 Nov 2009; 1:33 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Teddy Cheung (ccheung@milkyway.gsfc.nasa.gov)

Subjects: Gamma Ray, >GeV, Transients
Referred to by ATEL #: 2310

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed an increasing gamma-ray flux from a source positionally consistent with the flat spectrum radio quasar GB6 B1310+4844 (VLBI position: R.A. = 13:12:43.354, Dec. = +48:28:30.94, J2000, Beasley et al. 2002, ApJS, 141, 13). Preliminary analysis indicates that the source on November 18, 2009 was in a high state with a gamma-ray flux (photon energy E>100MeV) of (1.0 +/-0.2) x 10^-6 photons cm^-2 s^-1 (errors are statistical only), which represents an increase of a factor of about 40 with respect to the average source flux level during the first 11 months of the Fermi mission.

An optical spectrum obtained with the Hobby-Eberly Telescopes indicates a redshift z=0.501 (CGRaBS J1312+4828; Healey at al. 2008, ApJS, 175, 97) -- see the linked spectrum below. Note that the previously reported value (z=0.313) by Falco et al. (1998, ApJ, 494, 47) was indicated as a "marginal measurement."

Radio observations conducted with RATAN-600 in June 2003 show a flat radio spectrum on the level of about 0.2 Jy. Existing VLBA images from July 17, 2006 at 4.8 GHz (Helmboldt et al. 2007 ApJ, 658, 203) and August 10, 1996 at 2.3 and 8.4 GHz (http://astrogeo.org/vcs/), show an isolated, compact radio core which is expected for a faint blazar (extended structure, if present, would not be detected during short VLBA observations).

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).

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.

Hobby-Eberly Telescope optical spectrum


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