Fermi-LAT detection of enhanced gamma-ray activity from the FSRQ TXS 0724+571
ATel #17222; S. Wagner (University of Wuerzburg) and Pietro Monti-Guarnieri (University of Trieste) on behalf of the Fermi Large Area Telescope Collaboration
on 5 Jun 2025; 19:33 UT
Credential Certification: Sarah Wagner (sarah.wagner@physik.uni-wuerzburg.de)
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 enhanced gamma-ray activity from a source positionally consistent with the flat-spectrum radio quasar TXS 0724+571, also known as 4FGL J0729.1+5703 (Abdollahi et al. 2022, ApJS, 260, 53), with coordinates R.A. = 112.20680 deg, Dec. = +57.02344 deg (J2000; Xu et al. 2019, ApJS, 242, 5), and redshift z = 0.426 +/- 0.001 (Henstock et al. 1997, MNRAS, 290, 380â400).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on June 4, 2025, with a daily averaged gamma-ray flux (E>100MeV) of (0.4 +/- 0.1) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 150 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 +/- 0.2, indicating a significantly harder spectrum than the 4FGL value of 2.33 +/- 0.13.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. A preliminary light curve for TXS 0724+571 can be accessed via the Fermi-LAT Light-Curve Repository. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Sarah Wagner (sarah.wagner@uni-wuerzburg.de).
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.
