Fermi-LAT detection of a new gamma-ray source associated with the Radio Source TXS 1727+488

ATel #17299; C. Bartolini (University of Trento & INFN Bari), G. La Mura (INAF - Astronomical Observatory of Cagliari), P. Monti-Guarnieri (University of Trieste & INFN Trieste), on behalf of the Fermi Large Area Telescope Collaboration
on 22 Jul 2025; 17:49 UT
Credential Certification: Chiara Bartolini (chiara.bartolini-1@unitn.it)

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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 with coordinates R.A. = 262.25 deg, Dec. = +49.01 deg and 95% confidence uncertainty radius of 0.23 deg. This source is not in any published LAT catalog and was not detected by AGILE or EGRET. The localization uncertainty region includes the radio source TXS 1727+488, with coordinates R.A. = 262.27006 deg, Dec. = 48.79791 deg (Helfand et al. 2015, ApJ, 801, 26) and unknown redshift.

Preliminary analysis indicates that this source was significantly detected (>5 sigma) in a high gamma-ray state on July 19, 2025, with a daily averaged gamma-ray flux (E>100MeV) of (0.5+/-0.1) X 10^-6 photons cm^-2 s^-1 and a single power-law photon index of 2.2+/-0.2 (statistical uncertainties only). Further analysis of the time range covering from July 18, 2025 at 00:00 UT to July 20, 2025 at 23:59 improved the gamma-ray localization, resulting in a detection at R.A. = 262.37 deg, Dec. = 48.96 deg and 95% uncertainty radius of 0.17 deg, strengthening the case for the association with TXS 1727+488.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Chiara Bartolini (Chiara.Bartolini@ba.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.