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Fermi LAT Detection of Brightening of the Galactic Plane Source 3EG J0903-3531

ATEL # 1771; E. Hays, C.C. Cheung (NASA/GSFC), L. Reyes (U. Chicago), on behalf of the Fermi Large Area Telescope Collaboration
on 8 Oct 2008; 21:17 UT
Distributed as an Instant Email Notice (Transients)
Password Certification: Teddy Cheung (ccheung@milkyway.gsfc.nasa.gov)

Subjects: Gamma Ray, >GeV, Transients

The Large Area Telescope (LAT), one of two instruments on the Fermi Gamma-ray Space Telescope (formerly GLAST, launched June 11, 2008), has observed an increase in flux from a gamma-ray source in the Galactic Plane consistent with the location of 3EG J0903-3531 (R. Hartman et al. 1999, ApJS, 123, 79) starting on 6 October 2008. The preliminary LAT position is J2000.0: RA=136.25 deg, DEC=-35.45 deg (l=259.59 deg, b=+7.73 deg) with an error circle radius 0.08 deg (statistical). The systematic error on the location is smaller than the statistical error.

Preliminary analysis indicates that the source has brightened, with a gamma-ray flux (E>100MeV) exceeding previous levels detected by EGRET (average EGRET flux: 1.6x10-7 photons cm-2 s-1; peak flux 3.2x10-7 photons cm-2 s-1). The source activity did not reach the public reporting threshold of 2x10-6 photons cm-2 s-1 that would trigger a public data release.

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the activity of this source we strongly encourage multiwavelength observations. For this source the Fermi LAT contact person is C.C. Cheung (e-mail: Teddy.Cheung@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.


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