Fermi LAT detection of enhanced gamma-ray activity from the FSRQ PKS 2208-137
ATel #17072; F. Casaburo (INAF - Astronomical Observatory of Rome, Sapienza University Rome, INFN - Rome Tor Vergata), D. Bernard (LLR, Ecole Polytechnique & CNRS / IN2P3), S. Ciprini (INFN - Rome Tor Vergata, ASI- SSDC), on behalf of the Fermi Large Area Telescope Collaboration
on 10 Mar 2025; 15:46 UT
Credential Certification: Giovanni La Mura (giovanni.lamura@inaf.it)
Subjects: Gamma Ray, AGN, Blazar, Quasar
Referred to by ATel #: 17105
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 2208-137, also known as 4FGL J2211.2-1325 (4FGL catalog; The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 332.85041 deg, Dec. = -13.46937 deg (J2000; Truebenbach & Darling 2017, Truebenbach & Darling 2017, ApJS, 233, 3). This blazar redshift is z = 0.392 (Jones et al., 2009, MNRAS, 399, 683).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on March 5, 2025, with a daily averaged gamma-ray flux (E>100MeV) of (0.6+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 30 relative to the average flux reported in the 4FGL-DR4 (arXiv:2307.12546). This is the highest LAT daily flux ever observed for this source. The corresponding photon index is 2.4+/-0.3, and is consistent with the 4FGL value of 2.68+/-0.05 within the uncertainties.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. A preliminary light curve for PKS 2208-137 can be accessed via the Fermi-LAT Light-Curve Repository. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person are Fausto Casaburo (fausto[dot]casaburo[at]roma2[dot]infn[dot]it) and Stefano Ciprini (stefano[dot]ciprini[at]roma2[dot]infn[dot]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.
