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Fermi LAT Detection of a New Galactic Bulge Gamma-ray Transient in the Scorpius Region: Fermi J1750-3243, and its Possible Association with Nova Sco 2012

ATel #4284; C. C. Cheung (NRC/NRL), T. Glanzman, A. B. Hill (SLAC); on behalf of the Fermi Large Area Telescope Collaboration
on 28 Jul 2012; 18:01 UT
Credential Certification: Teddy Cheung (ccheung@milkyway.gsfc.nasa.gov)

Subjects: Gamma Ray, >GeV, Nova, Transient

Referred to by ATel #: 4287, 4288, 4310, 4408, 5302, 5525

The Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope, has detected a transient gamma-ray source in the Galactic Bulge: Fermi J1750-3243. Preliminary analysis of the Fermi-LAT data indicates that from 2012 June 18-24, the source was detected with a >100 MeV flux of (0.8 +/- 0.1) x 10^-6 ph cm^-2 s^-1 (statistical only; a systematic uncertainty of 30% should be added to this number) with >10 sigma significance. The source was detected with >3 sigma significance on a daily basis as early as June 16 and up to June 30. There is no previously reported gamma-ray source at this location.

Combining data for the 2-week period from June 16.0-30.0, the preliminary LAT position is (J2000.0): RA = 267.727 deg, Dec = -32.720 deg (l, b = 357.342 deg, -2.924 deg) which is in the Scorpius region of our Galaxy. Within the 95% confidence error circle radius of 0.122 deg (statistical only) is Nova Sco 2012, with a reported dramatic optical brightening of 6 mag from ~June 1-3 by Wagner et al. (CBET #3136, ATEL #4157), reaching a peak/plateau around June 19-21 (AAVSO lightcurve), when the gamma-ray light curve measured by the LAT peaked at fluxes of ~1 x 10^-6 ph cm^-2 s^-1.

After the gamma-ray nova discovery in the symbiotic binary V407 Cyg (CBET #2199, ATEL #2487; The Fermi LAT collaboration 2010, Science, 329, 817), this would be the second case of a gamma-ray transient detection from a nova by the Fermi-LAT.

Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of its possible association with Novs Sco 2012, we strongly encourage multiwavelength observations. For this source the Fermi LAT contact persons are C.C. Cheung (Teddy.Cheung.ctr@nrl.navy.mil) and A.B. Hill (A.Hill@soton.ac.uk).

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.