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Fermi LAT detection of a new transient gamma-ray source in the Galactic Plane through the Fermi All-sky Variability Analysis (FAVA)

ATel #6098; D. Kocevski (GSFC/NASA), M. Ajello (Clemson University), R. Buehler (DESY/Zeuthen), J. Becerra (GSFC/NASA), R. Ojha (GSFC/NASA) on behalf of the Fermi Large Area Telescope Collaboration
on 25 Apr 2014; 01:51 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Marco Ajello (majello@clemson.edu)

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

Referred to by ATel #: 6100, 6122, 6139

During the week between April 14 and April 21, 2014, the Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, observed gamma-ray activity from a previously unidentified transient source in the Galactic plane. The significance of the source detection above 100 MeV for the entire LAT exposure from April 14 and April 21, 2014 is approximately 7 sigma. The preliminary best-fit location of the gamma-ray source is RA = 100.383 deg, Dec = -3.294 deg, J2000, with 95% confidence that the source is within 0.25 deg of this position (statistical errors only). A preliminary spectral analysis of the source indicates that the source brightened in gamma rays to a flux (E > 100 MeV) of (7.7+/-1.3) x10^-7 ph cm^-2 s^-1, with a spectral index of 2.67 +/- 0.16 (errors are statistical only). A search of the NASA Extragalactic Database (NED) within the 95% containment radius reveals a bright flat-spectrum radio source, PMN J0641-0320, that is approximately 0.1 degrees from the LAT localization. A Swift ToO has been submitted and accepted for this source. Because Fermi provides all-sky coverage, regular gamma-ray monitoring of this source will continue. Multiwavelength observations during the ongoing activity of this source are strongly encouraged. The Fermi LAT contact person for Fermi J0641-0317 is Daniel Kocevski (e-mail: daniel.kocevski@nasa.gov). The transient was identified thanks to a new method implemented within the Fermi-LAT Collaboration known as `Fermi All-sky Variability Analysis' that searches the sky for high-energy transients on weekly time scales (Ackermann et al. 2013, ApJ, 771, 57). 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.