Fermi-LAT detection of renewed gamma-ray activity from the FSRQ S3 0458-02

ATel #17753; S. Rani (Michigan Technological University), E. Bronzini (INAF-OAS), T. Lewis (Michigan Technological University) on behalf of the Fermi Large Area Telescope Collaboration
on 14 Apr 2026; 21:15 UT
Credential Certification: Giovanni La Mura (giovanni.lamura@inaf.it)

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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 April 13, 2026, with a daily averaged gamma-ray flux (E>100 MeV) of (1.2 +/- 0.8) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of more than 10 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 2.1 +/- 0.2, indicating a slightly 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 #17544, #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. This source is one of the "LAT Monitored Sources" and consequently a preliminary estimation of the daily gamma-ray flux observed by Fermi LAT is publicly available (http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/PKS_0458-02). 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.