Fermi-LAT detection of renewed gamma-ray activity from the FSRQ OI 280
ATel #17394; F. Longo (University of Trieste and INFN Trieste) and A. Holzmann Airasca (University of Trento and INFN Bari), on behalf of the Fermi Large Area Telescope Collaboration
on 17 Sep 2025; 19:04 UT
Credential Certification: Francesco Longo (francesco.longo@ts.infn.it)
Subjects: Gamma Ray, >GeV, 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 flat-spectrum radio quasar OI 280, also known as 4FGL J0750.8+1229 (Abdollahi et al. 2020, ApJS, 247, 33), with coordinates R.A. = 117.71686 deg, Decl. = +12.51801 deg (J2000, Le Bail et al., 2016, AJ, 151, 79), and redshift z=0.889 (Jin et al. 2023, ApJS, 265, 25).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on September 16, 2025, with a daily averaged gamma-ray flux (E>100MeV) of (0.6+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 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 is the highest LAT daily flux ever observed for this source. The corresponding photon index is 2.0+/-0.2 indicating a significantly harder spectral state than the one inferred from the average power-law spectral index of 2.44 +/- 0.03 reported in 4FGL-DR4. The Fermi LAT Collaboration has previously reported flaring activity from this source in ATel #17181.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. A preliminary light curve for OI 280 can be accessed via the Fermi-LAT Light-Curve Repository at 4FGL J0750.8+1229. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Sarah Wagner (sarah.wagner@uni-wuerzburg.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.
