Fermi-LAT detection of enhanced gamma-ray activity from PKS 1954-388 and PKS 0131-522
ATel #15784; S. Joffre (Clemson University, USA), G. La Mura (LIP, Portugal), on behalf of the Fermi Large Area Telescope Collaboration
on 1 Dec 2022; 17:32 UT
Credential Certification: Giovanni La Mura (glamura@lip.pt)
Subjects: Gamma Ray, 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 enhanced gamma-ray activity from one 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 coordinates R.A. = 299.49925 deg, Decl. = -38.75177 deg (J2000; Ma et al. 1998, AJ, 116, 516), and redshift z=0.630 (Browne, Savage & Bolton 1975, MNRAS, 173, 87P; Tadhunter et al. 1993, MNRAS, 263, 999).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on November 29, 2022, with a daily averaged gamma-ray flux (E>100MeV) of (1.0+/-0.3) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of about 20 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). The corresponding photon index is 2.1 +/- 0.2, slightly harder than the 4FGL value of 2.34+/-0.02, yet, similar to what has been previously observed (ATels: #8063, #14346, #15274, #15326). A preliminary light-curve for this source can be found at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/PKS_1954-388.
Also on November 29, 2022 the LAT has observed enhanced/recurring gamma-ray flaring activity from a source positionally consistent with the flat-spectrum radio quasar PKS 0131-522, also known as 4FGL J0133.1-5201 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 23.27401, Decl. = -52.00110 (J2000; Johnston et. al. 1995, AJ, 110, 880), and a tentative redshift z=0.020 (Johnston et al. 1995, AJ, 110, 880). Flaring activity of PKS 0131-522 in LAT observations has been reported on several occasions (ATels #6233 #6256, #10987, #11003). A preliminary light-curve for PKS 0131-522 is regularly updated at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/PKS_0131-522.
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on November 29, 2022, with a daily averaged gamma-ray flux (E>100MeV) of (0.8+/- 0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of about 28 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). The corresponding photon index is 2.1+/-0.1, which is slightly harder than the 4FGL value of 2.32 +/- 0.02.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of these sources will continue. We encourage multifrequency observations of these sources. The Fermi-LAT contact person is Giacomo Principe (giacomo.principe@ts.inf.it) for PKS 1954-388 and Josefa Becerra (josefa.becerra@nasa.gov) for PKS 0131-522.
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.
