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Fermi-LAT detection of hard spectrum and high-level gamma-ray flare from the blazar PKS 1954-388

ATel #8063; Sara Cutini (ASDC Rome & INFN Perugia, Italy), Stefano Ciprini (ASDC Rome & INFN Perugia, Italy), on behalf of the Fermi Large Area Telescope Collaboration.
on 17 Sep 2015; 18:50 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 two instruments on the Fermi Gamma-ray Space Telescope, has observed flaring gamma rays from a source positionally consistent with the flat spectrum radio quasar PKS 1954-388 (also known as MRC 1954-388, RX J1958.0-3845, and 3FGL J1958.0-3847, Acero et al. 2015, ApJS 218, 23), with radio coordinates, (J2000.0), R.A.: 299.499247 deg, Dec.: -38.751766 deg, (Ma et. al. 1998, AJ, 116, 516). This FSRQ has a redshift of z=0.63 (Browne, Savage & Bolton 1975, MNRAS, 173, 87P).

Preliminary analysis indicates that on 16 September 2015 the source was in a high-flux state, with a daily gamma-ray flux (E>100MeV) of (1.0+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only) corresponding to a flux increase of a factor of about 17 with respect to the averaged flux reported in the Fermi LAT Third Source Catalog (3FGL). The corresponding spectral photon index (E>100MeV) of 1.9+/-0.1 is smaller than the average index of 2.228+/-0.052 in the 3FGL catalog. The source is detected in the same daily interval also in the energy band E>1GeV.

This is the first time that Fermi is announcing increased gamma-ray activity from PKS 1954-388. Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. In consideration of the ongoing activity and hard-state of this source, we encourage multiwavelength observations. For this source the Fermi LAT contact person is S. Cutini (sara.cutini@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.