Fermi-LAT detection of flaring GeV gamma-ray activity from the FSRQ OI 280 (PKS 0748+126)
ATel #17573; Stefano Ciprini (INFN Roma Tor Vergata & SSDC ASI), on behalf of the Fermi Large Area Telescope Collaboration)
on 4 Jan 2026; 21:12 UT
Credential Certification: Stefano Ciprini (stefano.ciprini@ssdc.asi.it)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Quasar
Referred to by ATel #: 17731
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed renewed and elevated gamma-ray activity from a source positionally consistent with the flat-spectrum radio quasar OI 280, also known as PKS 0748+126 and 4FGL J0750.8+1229 (The Fermi-LAT collaboration 2020, ApJS, 247, 33) with coordinates R.A. = 117.71686 deg, Decl. = +12.51801 deg (J2000, Le Bail et al., 2016, AJ, 151, 79). The redshift of OI 280 is z=0.889 (Torrealba et al. 2012, RMxAA, 48, 9).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state all the week of December 27-January 2, with daily averaged gamma-ray flux levels (E>100MeV) around 10^-6 photons cm^-2 s^-1, and reaching a peak daily gamma-ray flux (E>100MeV) of (1.3+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainties only) on both December 31, 2025 and January 2, 2026, corresponding to a flux increase of a factor >60 with respect 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), and doubling the flux reported in the previous LAT Collaboration ATel#17394. This level of December 31 and January 2 is the highest LAT daily flux ever observed for OI 280.
The corresponding photon index is 1.6+/-0.2 and 2.0+/-0.2 respectively, indicating a significantly harder spectral state than the one inferred from the average power-law spectral photon index of 2.44 +/- 0.03 reported in 4FGL-DR4 catalog. Several high-energy photons with energy between 10 and 20 GeV have been detected during this flaring period in spatial and temporal coincidence with this flat-spectrum radio quasar source, and, in particular, a 29 GeV energy photon was detected on January 1, 2026. The Fermi LAT Collaboration has previously reported flaring activity from this source in ATel#17394 and ATel#17181.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this flat spectrum radio quasar will continue. A preliminary light curve for OI 280 (PKS 0748+126) can be accessed via the Fermi-LAT Light-Curve Repository at 4FGL J0750.8+1229. This source is being added to the list of daily monitored LAT sources. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Sarah Wagner (sarah.wagner[at]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.
