Fermi-LAT detection of renewed gamma-ray activity from the BL Lac PMN J1315-5334
ATel #17244; Pietro Monti-Guarnieri (University of Trieste and INFN Trieste), Richard J. Britto (University of the Free State), on behalf of the Fermi Large Area Telescope Collaboration
on 24 Jun 2025; 22:01 UT
Credential Certification: Richard Britto (dr.richard.britto@gmail.com)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Blazar
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 BL Lac PMN J1315-5334, also known as 4FGL J1315.1-5333 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 198.76742 deg, Dec. = -53.57663 deg (J2000; Xu et al. 2019, ApJS, 242, 5), and unknown redshift.
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on June 23, 2025, with a daily averaged gamma-ray flux (E>100MeV) of (1.1+/- 0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of about 30 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 flux is about 2.5 times the one observed on April 23, 2025 (ATEL #17162) and similar to the flux observed on September 18, 2021 (ATEL #14929). However, the corresponding photon index is 2.04 +/- 0.13, indicating a significantly harder spectrum than reported during previous outbursts or in 4FGL-DR4, where the long-term average spectrum has an index of 2.43+/-0.03. We observed two photons with energies >10 GeV associated with the source with p > 0.999 and p>0.994, with energies of 16 and 17.5 GeV, respectively.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. Preliminary Fermi-LAT light curves for PMN J1315-5334 can be accessed via the Monitored Source List, and via the Fermi-LAT Light-Curve Repository. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Isabella Mereu (mereuisabella@gmail.com).
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.
