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Fermi LAT detection of a GeV flare from B2 0619+33

ATEL # 2829; F.K. Schinzel (MPIfR) on behalf of the Fermi LAT Collaboration
on 6 Sep 2010; 14:09 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Frank Schinzel (

Subjects: Gamma Ray, >GeV, Request for Observations, Transients
Referred to by ATEL #: 2831, 2848, 2849

The Large Area Telescope (LAT), one of the two instruments on board the Fermi Gamma-ray Space Telescope, has observed an increased gamma-ray flux from a source positionally consistent with the radio source B2 0619+33/VCS J0622+3326 (RA: 06h22m52.221945s, Dec: +33d26m10.41027s, J2000; Kovalev et al. 2007, AJ 133, 1236).

The source was detected in a high state September 1-4, 2010. Preliminary analysis indicates that on September 3, 2010 the flare reached a peak gamma-ray flux (E>100MeV) of 1.0 +/-0.2*10^-6 photons cm^-2 s^-1 (errors are statistical only). An improved gamma-ray source localization was obtained integrating data from September 1-4, 2010 resulting in R.A.: 06h22m40.96s, Dec.: +33d26m26.47s (J2000) with a 95% confidence error circle radius of 0.10 degree. The closest cataloged gamma-ray source is 1FGL J0623.5+3330, 0.25 degree from the location of the flaring source. If the flare is attributable to 1FGL J0623.5+3330, then the flux from September 3, 2010 represents an increase by a factor of at least 50 for E>100MeV (a factor of about 80 for 1-100 GeV) relative to its average level during August 2008-July 2009 (Abdo et al. 2010, ApJS 188, 405).

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. The Fermi LAT contact person for this source is Frank Schinzel ( In consideration of the ongoing activity of this source we strongly encourage multi-wavelength observations.

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.

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R. E. Rutledge , Editor
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