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Fermi LAT Detection of a New Gamma-ray Transient in the Galactic Plane: Fermi J0639+0548

ATel #4224; C. C. Cheung (NRC/NRL), E. Hays, T. Venters, D. Donato (NASA/GSFC), R. H.D. Corbet (UMBC, NASA/GSFC); on behalf of the Fermi Large Area Telescope Collaboration
on 29 Jun 2012; 01:53 UT
Credential Certification: Teddy Cheung (ccheung@milkyway.gsfc.nasa.gov)

Subjects: Gamma Ray, >GeV, Request for Observations, Transient

Referred to by ATel #: 4310, 4320, 4321, 4352, 4365, 4376, 4408, 4542, 4569, 4572, 4590, 4709, 4727, 4764, 4845, 4907, 5499, 7744

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 2012 Jun 22. Using data from Jun 18.0 - 26.4, the preliminary LAT position is (J2000.0): RA = 99.91 deg, Dec = 5.81 deg, (l, b = 206.42 deg, 0.03 deg) with a 68% confidence error circle radius 0.12 deg (statistical uncertainty only).

Preliminary analysis of the Fermi-LAT data indicates that the source was detected on three consecutive days (2012 Jun 22-24) with significances of ~5 sigma, and fluxes (E >100 MeV) of (1.0 +/- 0.4) x 10^-6 ph cm^-2 s^-1 to (1.5 +/- 0.5) x 10^-6 ph cm^-2 s^-1 (statistical uncertainties only).

The source was not detected previously by the LAT and there is no previously reported EGRET gamma-ray detection at this location. The nearest known gamma-ray source is 0.9 deg away (2FGL J0636.0+0554). There are no obvious candidate lower-energy counterparts to this transient.

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the ongoing activity of this source we strongly encourage multiwavelength observations. Note that this source is currently Sun constrained for Swift. For this source the Fermi LAT contact persons are C.C. Cheung (Teddy.Cheung.ctr@nrl.navy.mil) and E. Hays (elizabeth.a.hays@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.