Fermi-LAT detection of a GeV flare from blazar TXS 0646-176
ATel #7833; Stefano Ciprini (ASI Science Data Center, Rome, & INFN Perugia, Italy), on behalf of the Fermi Large Area Telescope Collaboration
on 24 Jul 2015; 15:04 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@asdc.asi.it)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Blazar, Quasar
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed increasing gamma-ray flux from a source positionally consistent with the flat spectrum radio quasar TXS 0646-176 , also known as MRC 0646-176 and 3FGL J0648.8-1740, with radio counterpart position R.A.: 102.11874 deg, -17.73484 deg, (J2000.0, Petrov et al. 2006, AJ, 131, 1872 ) and with redshift z=1.232 (Hewitt & Burbidge 1993, ApJS, 87, 451).
Preliminary analysis indicates that on 2015 July 21, the blazar TXS 0646-176 was in a high state with a daily averaged gamma-ray flux (E>100 MeV) of (0.8+/-0.2) X 10^-6 photons cm^-2 s^-1, and a 6-hour (12:00-18:00 UT) interval peak gamma-ray flux of (1.4+/-0.4) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 60 times greater than the average flux reported in the third Fermi-LAT source catalog, 3FGL (Acero et al. 2015, ApJS 218, 23). The corresponding spectral photon index (E>100MeV) of respectively (2.5+/-0.3) and (2.6+/-0.4) are in line with the average index of 2.520+/-0.119 in the 3FGL catalog.
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 encourage multiwavelength observations. For this source the Fermi LAT contact person is S. Ciprini (stefano.ciprini@asdc.asi.it).
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.