Fermi-LAT detection of enhanced gamma-ray activity from the FSRQ Ol 280
ATel #17181; S. Wagner (University of Wuerzburg), Giovanni La Mura (INAF-O. A. Cagliari), C. Bartolini (University of Trento & INFN Bari) on behalf of the Fermi Large Area Telescope Collaboration
on 12 May 2025; 18:22 UT
Credential Certification: Sarah Wagner (sarah.wagner@physik.uni-wuerzburg.de)
Subjects: Gamma Ray, >GeV, AGN, Blazar, Quasar
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed enhanced gamma-ray activity from a source positionally consistent with the flat-spectrum radio quasar Ol 280, also known as 4FGL J0750.8+1229 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with radio coordinates R.A. = 117.71686 deg, Decl. = +12.51801 (J2000, Le Bail et al., 2016, AJ, 151, 79), and redshift z= 0.889 (Jin et al. 2023, ApJS, 265(1), 25).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on May 11, 2025, with a daily averaged gamma-ray flux (E>100MeV) of (0.4 +/- 0.1) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 20 relative to the average flux reported in the fourth data release of 4FGL (4FGL-DR4; Ballet et al. 2024, arXiv:2307.12546). The corresponding photon index is 1.8 +/- 0.2, indicating a significantly harder spectral state than the 4FGL-DR4 value of 2.44 +/- 0.04.
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 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.
