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Fermi LAT detection of a GeV flare from blazar S5 1803+784

ATEL # 2386; D. Donato (NASA/GSFC), on behalf of the Fermi Large Area Telescope Collaboration
on 13 Jan 2010; 19:33 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Teddy Cheung (

Subjects: Gamma Ray, >GeV, AGN, Quasars

The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope has observed an increasing gamma-ray flux from a source positionally coincident with the BL Lac object S5 1803+784 (RA=18h00m45.7s, DEC= +78d28'04.0", J2000, Johnston et al. 1995, AJ, 110, 880; z=0.68, Heeschen et al. 1987, AJ, 94, 1493).

Preliminary analysis indicates that on January 11, 2010, the source was in a high state, with a gamma-ray flux (E>100MeV) of (0.9 +/- 0.2)*10^-6 photons/cm^2/s (statistical uncertainty only), representing more than an order of magnitude increase over its average flux during the first 11 months of Fermi observations.

Since Fermi operates in an all-sky scanning mode, regular monitoring of this source will continue. In consideration of the ongoing activity of this source we strongly encourage multiwavelength observations. The Fermi LAT contact person for this source is Davide Donato (

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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