Fermi-LAT detection of enhanced gamma-ray activity from the FSRQ S5 1053+70
ATel #17517; P. Monti-Guarnieri (University of Trieste and INFN Trieste), on behalf of the Fermi Large Area Telescope Collaboration
on 1 Dec 2025; 17:39 UT
Credential Certification: Giovanni La Mura (giovanni.lamura@inaf.it)
Subjects: Gamma Ray, 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 S5 1053+70, also known as 4FGL J1056.8+7012 (Abdollahi et al. 2022, ApJS, 260, 53), with coordinates R.A. = 164.22341 deg, Dec. = +70.19609 deg (J2000, Fey et al. 2015, AJ, 150, 58), and redshift z=2.492 (Xu et al. 1994, AJ, 108, 395).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on November 30, 2025, with a daily averaged gamma-ray flux (E>100MeV) of (0.31+/-0.09) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 15 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). The corresponding photon index is 2.3+/-0.2, indicating a harder spectrum than the 4FGL-DR4 value of 2.66+/-0.03.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. A preliminary light curve for S5 1053+70 can be accessed via the Fermi-LAT Light-Curve Repository at 4FGL J1056.8+7012. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Pietro Monti-Guarnieri (pietro.monti-guarnieri@phd.units.it).
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.
