Fermi-LAT detection of enhanced gamma-ray activity from FSRQ S5 1027+74
ATel #17534; P. van Zyl (South African Radio Astronomy Observatory Hartebeesthoek), C. Bartolini (University of Trento & INFN Bari), G. La Mura (INAF - OACa), F. Casaburo (INAF - OAR, Sapienza University of Rome, INFN Tor Vergata), on behalf of the Fermi Large Area Telescope Collaboration
on 9 Dec 2025; 16:01 UT
Credential Certification: Pfesesani van Zyl (pfesi24@gmail.com)
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 (FSRQ) S5 1027+74, also known as 4FGL J1031.1+7442 (Abdollahi et al. 2022, ApJS, 260, 53), with coordinates R.A. = 157.84177 deg, Dec. = +74.69954 deg (J2000, Hunt et al. 2021, AJ, 162, 121), and redshift z=0.123 (Stickel and Kuhr 1993, A&AS, 100, 395).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on December 8, 2025, with a daily averaged gamma-ray flux (E>100MeV) of (1.1+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 130 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 2.6+/-0.2, indicating a softer spectrum than the 4FGL-DR4 value of 2.18+/-0.07.
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 1027+74 can be accessed via the Fermi-LAT Light-Curve Repository at 4FGL J1031.1+7442. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Pfesi van Zyl (pvanzyl@sarao.ac.za).
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.
