Fermi-LAT detection of renewed gamma-ray activity from the flat-spectrum radio source TXS 2138+527
ATel #17584; Chiara Bartolini (University of Trento & INFN Bari) on behalf of the Fermi Large Area Telescope Collaboration
on 8 Jan 2026; 07:29 UT
Credential Certification: Chiara Bartolini (chiara.bartolini-1@unitn.it)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Blazar, Quasar
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed gamma-ray emission from a source positionally consistent with the flat-spectrum radio source TXS 2138+527, with radio coordinates R.A. = 324.97344 deg, Dec. = 53.00461 deg (J2000; Immer et al. 2011, ApJS, 194, 25), and unknown redshift. This source is not yet in any published LAT catalog and was not detected by AGILE or EGRET, but was already observed in the past by the LAT (ATel #16760).
Preliminary analysis indicates that this source was significantly detected (>5 sigma) in a high gamma-ray state on 2026 January 6, with a daily averaged gamma-ray flux (E>100MeV) of (1.3+/-0.2) X 10^-6 photons cm^-2 s^-1 and a single power-law photon index of 2.1+/-0.1 (statistical uncertainties only). The level of flaring activity seen on January 6 is the highest LAT daily flux ever observed for TXS 2138+527.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of TXS 2138+527 will continue and the source will be added to the list of daily monitored LAT sources, thus providing a preliminary light curve. We encourage multifrequency observations of this source. The Fermi-LAT contact person for TXS 2138+527 is C. C. Cheung (chi.c.cheung2.civ at us.navy.mil).
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.
