Fermi-LAT detection of renewed gamma-ray activity from OP 313
ATel #17167; P. V van Zyl (South African Radio Astronomy Observatory, SARAO), P. Monti-Guarnieri (University of Trieste and INFN Trieste)
on 5 May 2025; 16:00 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Pfesesani van Zyl (pfesi24@gmail.com)
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 OP 313, also known as 4FGL J1310.5+3221 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 197.61943 deg, Dec. = +32.34549 deg (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift z=0.997 (Schneider et al. 2010, AJ, 139, 2360).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on May 4, 2025, with a daily averaged gamma-ray flux (E>100MeV) of (3.8+/-0.3) x 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 70 times higher than the average flux reported in the fourth data release of 4FGL (4FGL-DR4; Ballet et al. 2024, 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 spectral state than the 4FGL-DR4 value of 2.23+/-0.01. The Fermi-LAT Collaboration has previously reported flaring activity from this source in ATels #6068, #15483, #16356, #16497, #16940, and #16970.
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 OP 313 can be accessed via the Monitored Source List, and via theFermi-LAT Light-Curve Repository. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Sara Buson (sara[DOT]buson[AT]astro[DOT]uni-wuerzburg[DOT]de).
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.
