Fermi-LAT detection of enhanced gamma-ray activity from the FSRQ PKS 1954-388
ATel #14346; F. D'Ammando (INAF-IRA Bologna) on behalf of the Fermi Large Area Telescope Collaboration
on 25 Jan 2021; 20:52 UT
Credential Certification: Filippo D'Ammando (dammando@ira.inaf.it)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Black Hole, Blazar, Quasar
Referred to by ATel #: 15784
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed enhanced gamma-ray activity from a source positionally consistent with the flat-spectrum radio quasar PKS 1954-388, also known as 4FGL J1958.0-3845 (The Fermi-LAT Collaboration 2020, ApJS, 247, 33), with radio coordinates, (J2000.0), R.A.: 299.499247 deg, Dec.: -38.751766 deg, (Ma et. al. 1998, AJ, 116, 516) and a redshift of z = 0.63 (Browne, Savage & Bolton 1975, MNRAS, 173, 87P).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state during 2021 January 19-24, with a daily averaged gamma-ray flux (E > 100 MeV) of (1.7 +/- 0.3) x 10^-6 photons cm^-2 s^-1 (statistical uncertainty only) on January 24. This corresponds to a flux increase of a factor of 25 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). The corresponding photon index is 1.9+/-0.1, significantly smaller than the 4FGL value of 2.34 +/- 0.02.
Gamma-ray flaring activity from PKS 1954-388 with a comparable hard spectrum was previously reported in 2015 September 16 (ATel #8063).
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source is included in the "LAT Monitored Sources" and consequently, a preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT will be publicly available ( Fermi LAT Monitored Source List Light Curves ). We encourage multi-frequency observations of this source. For this source, the Fermi-LAT contact person is S. Cutini (sara.cutini@pg.infn.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.
