Fermi-LAT detection of renewed gamma-ray activity from the FSRQ S3 0458-02
ATel #17544; Adithiya Dinesh (Universidad Complutense de Madrid), on behalf of the Fermi Large Area Telescope Collaboration
on 16 Dec 2025; 15:49 UT
Credential Certification: Adithiya Dinesh (adinesh@ucm.es)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Blazar
Referred to by ATel #: 17753
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed renewed gamma-ray activity from a source positionally consistent with the flat-spectrum radio quasar S3 0458-02, also known as 4FGL J0501.2-0158 (Abdollahi et al. 2022, ApJS, 260, 53), with coordinates R.A. = 75.30337 deg, Dec. = -1.98729 deg (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift z=2.286 (Strittmatter et al. 1974, ApJ, 190, 509).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on December 15, 2025, with a daily averaged gamma-ray flux (E>100MeV) of (0.7+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 7 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). The corresponding photon index is 2.0+/-0.2, indicating a significantly harder spectrum than the 4FGL-DR4 value of 2.37+/-0.01. The Fermi-LAT Collaboration has previously reported flaring activity from this source in ATels #16110, #7952, #5951, and #4396.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. A preliminary light curve for 4FGL J0501.2-0158 can be accessed via the Fermi-LAT Light-Curve Repository at 4FGL J0501.2-0158. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is M. Orienti (orienti@ira.inaf.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.
