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Fermi LAT Detection of a New Gamma-ray Transient in the Galactic Plane: J0910-5041

ATEL # 1788; C.C. Cheung (NASA/GSFC), L. Reyes (U. Chicago), F. Longo (INFN Trieste), G. Iafrate (INAF/OA Trieste) on behalf of the Fermi Large Area Telescope Collaboration
on 17 Oct 2008; 20:00 UT
Distributed as an Instant Email Notice (Transients)
Password Certification: Teddy Cheung (

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 detected a transient gamma-ray source in the Galactic Plane starting on October 15, 2008. The preliminary LAT position is (J2000.0): RA, Dec = 137.69 deg, -50.74 deg (l, b = 271.62 deg, -1.80 deg) with a 68% confidence error circle radius 0.07 deg (statistical). The systematic error on the location is smaller than the statistical error.

Preliminary analysis of the Oct 15 data shows a high-significance source (10 sigma), with a gamma-ray flux (E>100MeV) = (1.4 +/- 0.3) x 10-6 photons cm-2 s-1 with an additional 30% systematic uncertainty. The source was not detected previously by the LAT and there is no previously reported EGRET gamma-ray detection at this location. Furthermore, there is no obvious lower-energy counterpart.

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:

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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