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Fermi LAT Detection of a New Gamma-ray Transient in the Galactic Plane: J1057-6027

ATEL # 2081; H. Yasuda, H. Takahashi (Hiroshima University), W. McConville (NASA GSFC, UMD); on behalf of the Fermi Large Area Telescope Collaboration
on 12 Jun 2009; 22:21 UT
Distributed as an Instant Email Notice (Transients)
Password Certification: Teddy Cheung (

Subjects: Gamma Ray, >GeV, Transients
Referred to by ATEL #: 2082

The Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope, has detected a transient gamma-ray source in the Galactic Plane starting on 11 June 2009. Preliminary analysis of the Fermi-LAT data indicates that during the day of 11 June 2009, the source was detected with a flux (E >100 MeV) of 2.4 +/- 0.7 x 10^-6 ph cm^-2 s^-1 (statistical only). A systematic uncertainty of 30% should be added to this number. The preliminary analysis indicates that the source was detected at just above 5 sigma with a relatively soft spectrum.

The new gamma-ray transient is positionally consistent with a LAT source detected in 9-months (Aug 2008 - Apr 2009) of all-sky monitoring data. The preliminary LAT position from the 9-month data is (J2000.0): RA = 164.308 deg., Dec = -60.458 deg., (l, b = 289.301 deg, -0.645 deg) with a 95% confidence error circle radius 0.068 deg (statistical only). The new LAT detection indicates an increase of a factor of about 10 with respect to the source flux level detected during the earlier period. There is no previously reported EGRET gamma-ray detection at this location.

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 Hajimu Yasuda (

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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