Fermi-LAT detection of renewed gamma-ray activity from the FSRQ OL 256
ATel #17047; G. La Mura (INAF - Astronomical Observatory of Cagliari), on behalf of the Fermi Large Area Telescope Collaboration
on 20 Feb 2025; 21:52 UT
Credential Certification: Giovanni La Mura (giovanni.lamura@inaf.it)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Blazar, Quasar
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 OL 256, also known as 4FGL J1036.2+2202 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 159.13742 deg, Dec. = +22.05339 deg (J2000; Petrov et al 2011, AJ, 142, 89), and redshift z=0.595 (Hewett & Wild 2010, MNRAS, 405, 2302).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on February 19, 2025, with a daily averaged gamma-ray flux (E>100MeV) of (0.5+/-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 30 relative to the average flux reported in the fourth data release of the Fermi-LAT catalog (4FGL-DR4, Ballet et al. 2024, arXiv:2307.12546). The corresponding photon index is 2.1+/-0.2, indicating a harder spectrum than the 4FGL-DR4 value of 2.48+/-0.04. The spectral hardening led to the observation of one high energy photon with E=15 GeV and probability of being associated with the source p > 0.999. The Fermi-LAT Collaboration has previously announced flaring activity of OL 256 in ATel #14233.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. A preliminary light curve for OL 256 can be accessed via the Fermi-LAT Light-Curve Repository at 4FGL J1036.2+2202. 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.
