Fermi LAT Detection of a New Gamma-ray Transient near the Galactic Plane: Fermi J1717-5156
ATel #4023; F. K. Schinzel (UNM) & C. C.Cheung (NRC/NRL) on behalf of the Fermi Large Area Telescope Collaboration
on 9 Apr 2012; 18:03 UT
Credential Certification: Frank Schinzel (fsch@unm.edu)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Blazar, Quasar, Transient
The Large Area Telescope (LAT), on board the Fermi Gamma-ray Space Telescope, has detected a new transient gamma-ray source near the Galactic Plane on April 7, 2012 with a one-day peak flux (>100 MeV) of (1.0 +/- 0.3) e-6 ph cm^-2 s^-1. The source is not present in any Fermi LAT catalogs released up to now and there is no previously reported EGRET gamma-ray detection at this location, with the closest LAT source in the 2FGL catalog (Nolan et al. 2012, ApJS, 199, 31) being 2FGL J1710.5-5020 (1.9 deg away). From the 1-week Fermi-LAT data from April 1st (0 UT) - 8th (12 UT), the preliminary LAT position was determined (RA and DEC, J2000.0): 17:17:34.69, -51:55:31.9 (l = 337.776 deg, b = -8.072 deg) with a 95% confidence error circle radius of 0.18 deg.
The unidentified compact radio source, PMN J1717-5155 (RA and Dec, J2000.0: 17:17:34.691880, -51:55:31.92535; http://astrogeo.org/lcs/cat/), is consistent with the reported LAT position with a separation of 3.3 arcmin. Non-simultaneous flux density measurements (S = 165 mJy at 4.9 GHz, Wright et al. 1994 ApJS 91, 111; S = 393 mJy at 843 MHz, Murphy et al. 2007 MNRAS 382, 382) indicate a spectral index, alpha = 0.5 (S propto nu^-alpha), i.e., at the defining line between a steep-spectrum and flat-spectrum radio source.
Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. A Swift ToO observation will be performed to confirm the counterpart association. In consideration of the ongoing activity of this source we strongly encourage multi-wavelength observations. For this source the Fermi LAT contact person is Frank Schinzel (fsch@unm.edu).
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.
