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Fermi LAT Detection of a New Galactic Plane Gamma-ray Transient in the Cygnus Region: Fermi J2102+4542, and its Possible Association with V407 Cyg

ATel #2487; C. C. Cheung (NRC/NRL), D. Donato (NASA GSFC), E. Wallace (U. Washington), R. Corbet (NASA GSFC), G. Dubus (U. Grenoble), K. Sokolovsky (MPIfR), H. Takahashi (Hiroshima U.); on behalf of the Fermi Large Area Telescope Collaboration
on 18 Mar 2010; 16:52 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Julie McEnery (julie.mcenery@nasa.gov)

Subjects: Gamma Ray, >GeV, Transient

Referred to by ATel #: 2498, 2506, 2511, 2529, 2536, 2546, 2741, 2905, 4284, 4310, 4408, 5302

The Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope, has detected a transient gamma-ray source in the Galactic Plane: Fermi J2102+4542. Preliminary analysis of the Fermi-LAT data indicates that on the 13th and 14th of March 2010, the source was detected with a >100 MeV flux of (1.0 +/- 0.3) x 10^-6 ph cm^-2 s^-1 and (1.4 +/- 0.4) x 10^-6 ph cm^-2 s^-1, respectively (statistical only) -- corresponding significances on these days are 8 sigma and 6 sigma. A systematic uncertainty of 30% should be added to this number. There is no previously reported gamma-ray source at this location.

Combining data for the period from Mar 12 0:0:0 UTC and ending Mar 16 ~8:30 UTC, the preliminary LAT position is (J2000.0): RA = 315.60 deg., Dec = 45.71 deg. (l, b = 86.96 deg, -0.55 deg) which is in the Cygnus region of our Galaxy. There is no previously reported EGRET or LAT gamma-ray source at this position. Within the 95% confidence error circle radius of 0.12 deg (statistical only) is the symbiotic star V407 Cyg, with a reported optical outburst beginning approximately 2 days earlier (CBET #2199) than the onset of gamma-ray activity detected by the LAT. Swift/XRT observations triggered on the optical outburst of V407 Cyg and performed on March 13th and 15th resulted in 2.4-2.6 sigma (0.3-10 keV) detections of an X-ray source coincident with the position of the star in each of the two 960 sec exposures.

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 gamma-ray source, and its possible association with V407 Cyg, we strongly encourage multiwavelength observations of the star. For this source the Fermi LAT contact person is C.C. Cheung (Teddy.Cheung.ctr@nrl.navy.mil).

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.