Fermi-LAT detection of enhanced gamma-ray activity from the FSRQ PKS 2253-278
ATel #15351; G. La Mura (LIP, Portugal) and S. Ciprini (INFN Roma Tor Vergata & SSDC), on behalf of the Fermi Large Area Telescope Collaboration
on 28 Apr 2022; 14:30 UT
Credential Certification: Giovanni La Mura (glamura@lip.pt)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Blazar, Transient
On April 24, the Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed an unidentified transient located at R.A. = 343.643 deg, Decl. = 27.283 deg and 99% confidence containment radius of 0.333 deg. Two sources, listed in the fourth Fermi-LAT catalog (4FGL, The Fermi-LAT collaboration 2020, ApJS, 247, 33), were identified as potential candidates, namely 4FGL J2254.8-2725 (associated with the BL Lac type object NVSS J225453-272509) and 4FGL J2256.0-2740 (associated with the flat-spectrum radio quasar PKS 2253-278). Further observations of the source in the following 2 days resulted in a more constrained localization of the gamma-ray source at R.A. = 343.972 deg, Decl. = 27.591 deg and 99% confidence containment radius of 0.154 deg. This indicates that the most likely counterpart is PKS 2253-278, with coordinates R.A. = 344.000 deg, Decl. = -27.599 deg (J2000; Beasley et al. 2002, ApJS, 141, 13), and redshift z = 1.751 (Hutsemekers et al. 2017, A&A, 606, 101).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on April 26, 2022, with a daily averaged gamma-ray flux (E>100MeV) of (0.9+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of more than 20 relative to the average flux reported in 4FGL. This is the highest LAT daily flux ever observed for this source. The corresponding photon index is 2.7+/-0.2, and is smaller than the 4FGL value of 3.0+/-0.1.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact persons are G. La Mura (glamura@lip.pt) and S. Ciprini (stefano.ciprini@ssdc.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.
