Fermi-LAT detection of gamma-ray activity from the Seyfert 1 galaxy source PKS 0521-36

ATel #18032; F. Casaburo (INAF-OAR, INFN- Roma Tor Vergata, Sapienza University of Roma), S. Ciprini (INFN- Roma Tor Vergata, SSDC-AS) on behalf of the Fermi Large Area Telescope Collaboration
on 6 Sep 2026; 20:43 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 gamma-ray activity from a source positionally consistent with the Seyfert 1 galaxy PKS 0521-36, also known as 4FGL J0522.9-3628 (Abdollahi et al. 2022, ApJS, 260, 53), with coordinates R.A. = 80.74160 deg, Dec. = -36.45857 deg (J2000; Charlot et al. 2020, A&A, 644, 159), and redshift z=0.05655 +/-0.00018 (Jones et al. 2009, MNRAS, 389, 683).

Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on September 05, 2026, with a daily averaged gamma-ray flux (E>100MeV) of (1.5+/-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 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). This is the highest LAT daily flux ever observed for this source. The corresponding photon index is 2.0 +/- 0.1, indicating a significantly harder spectrum than the 4FGL-DR4 value of 2.45 +/- 0.01. The Fermi LAT Collaboration has previously reported gamma-ray flaring activity from PKS 0521-36 in ATel #2683.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source belongs to the "LAT Monitored Sources" and, consequently, a preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT is publicly available at PKS 0521-36. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is F. D'Ammando (filippo[dot]dammando[at]inaf[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.