Fermi-LAT detection of renewed gamma-ray activity from the FSRQ TXS 1235-117
ATel #17549; Adithiya Dinesh (Universidad Complutense de Madrid), on behalf of the Fermi Large Area Telescope Collaboration
on 18 Dec 2025; 16:35 UT
Credential Certification: Adithiya Dinesh (adinesh@ucm.es)
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 TXS 1235-117, also known as 4FGL J1238.5-1201 (Abdollahi et al. 2022, ApJS, 260, 53), with coordinates R.A. = 189.53091 deg, Dec. = - 11.99015 deg (J2000; Healey et al. 2007, ApJS, 171, 61), and redshift z=0.293 (Jones et al. 2009, MNRAS, 399, 683).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on December 17, 2025, with a daily averaged gamma-ray flux (E>100MeV) of (0.9+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 50 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+/-0.1, indicating a significantly harder spectrum than the 4FGL-DR4 value of 2.64+/-0.05. The Fermi-LAT Collaboration has previously reported flaring activity from this source in ATel #17349.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. A preliminary light curve for 4FGL J1238.5-1201 can be accessed via the Fermi-LAT Light-Curve Repository at 4FGL J1238.5-1201. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Francesco Longo (Francesco.Longo@ts.infn.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.
