Fermi-LAT detection of a GeV gamma-ray flare from the blazar PKS 1313-333

ATel #8533; Stefano Ciprini (ASI Science Data Center, Rome, & INFN Perugia, Italy), on behalf of the Fermi Large Area Telescope Collaboration
on 12 Jan 2016; 00:13 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@asdc.asi.it)

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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 PKS 1313-333 (also known as TXS 1313-333, OP -322, 2EG J1314-3430 and 3FGL J1316.0-3338), with radio counterpart position R.A.: 199.033275 deg, Dec.: -33.64977 deg, (J2000.0, Johnston et al. 1995, AJ, 110, 880) and with redshift z=1.210 (Jauncey et al. 1982, AJ, 87, 763).

Preliminary analysis indicates that on 2016 January 10, PKS 1313-333 was in a high state with a daily averaged gamma-ray flux (E>100 MeV) of (1.3+/-0.1) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 27 times greater than its four-year average flux reported in the third Fermi-LAT source catalog (3FGL, Acero et al. 2015, ApJS, 218, 23). The corresponding daily averaged spectral photon index (E>100 MeV) of 1.88+/-0.06 (statistical uncertainty only) is significantly harder than the 3FGL catalog value of 2.323+/-0.044.

Gamma-ray enhanced activity from PKS 1313-333 on weekly timescale has been recently reported in ATel#8483. The source is observed by the LAT to be active since about mid December 2015 and this is the first time that a such daily flux level is announced.

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.