Fermi-LAT detection of enhanced gamma-ray activity from the blazar PKS 0618-252
ATel #17340; A. Holzmann Airasca (University of Trento & INFN Bari) and G. La Mura (INAF - Astronomical Observatory of Cagliari), on behalf of the Fermi Large Area Telescope Collaboration
on 17 Aug 2025; 19:53 UT
Credential Certification: Chiara Bartolini (chiara.bartolini-1@unitn.it)
Subjects: Gamma Ray, >GeV, AGN, Blazar
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 blazar PKS 0618-252, also known as 4FGL J0620.5-2512 (Abdollahi et al. 2022, ApJS, 260, 53), with coordinates R.A. = 95.13382 deg, Dec. = -25.25485 deg (J2000; Hunt et al. 2021, AJ, 162, 121), and redshift z=1.9 (Cao et al. 2017, A&A 606, 15).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on August 16, 2025, with a daily averaged gamma-ray flux (E>100MeV) of (0.8+/-0.3) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 50 relative to the average flux reported in the fourth data release of the fourth Fermi-LAT catalog (4FGL-DR4, Ballet et al. 2023, arXiv:2307.12546). This is the highest LAT daily flux ever observed for this source. The corresponding photon index is 2.3+/-0.3, and is consistent with the 4FGL-DR4 value of 2.59+/-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 0618-252 can be accessed via the Fermi-LAT Light-Curve Repository at 4FGL J0620.5-2512. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Aldana Holzmann Airasca (a.holzmannairasca@unitn.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.
