Fermi LAT detection of a GeV flare from an unidentified source coincident with two FSRQs

ATel #3313; E. Hays and D. Donato (NASA/GSFC) on behalf of the Fermi LAT Collaboration
on 28 Apr 2011; 17:20 UT
Credential Certification: Davide Donato (davide.donato-1@nasa.gov)

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The Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope, has observed a gamma-ray flare from a source near two flat spectrum radio sources. The preliminary best-fit location of the gamma-ray source (RA=178.34 deg, DEC=49.56 deg, J2000) has a 95% containment radius of 0.12 deg (statistical errors only) for observations from April 23 0 UT to April 26 15:51 UT. This error circle contains 1150+497 (RA: 11h53m24.4666s, Dec: +49d31m08.830s, J2000, Johnston et al. 1995, AJ, 110, 880), a quasar with a prominent radio jet detected in the X-rays and at optical frequencies (Sambruna et al. 2002, ApJ, 571, 206) and located at z=0.334 (Lynds & Wills 1968, ApJ, 153, L23). A second candidate, BZQ J1152+4939 (RA: 11h52m32.8710s, Dec: +49d39m38.767s, J2000, Fomalont et al. 2003, AJ, 126, 2562, located at z=1.093, 2005, SDSS4), lies outside the 95% containment region and is less favorable as a counterpart.

Preliminary analysis indicates that the source brightened in gamma rays on April 24, 2011, with a daily flux (E>100MeV) of (0.8 +/- 0.2) x 10^-6 ph cm^-2 s^-1 (errors are statistical only). The average flux on April 25 increased to (1.5 +/- 0.3) x 10^-6 cm^-2 s^-1. The source was not detected previously by the LAT on daily timescales and this flux level is more than an order of magnitude above the long-term average. There is no previously reported EGRET gamma-ray detection at this location.

Because Fermi operates in all-sky survey mode, gamma-ray monitoring of this source will continue. In consideration of the activity of this source we strongly encourage multiwavelength observations. The Fermi LAT contact person for this source is E. Hays (elizabeth.a.hays@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.