Fermi-LAT detection of renewed gamma-ray activity from the FSRQ PKS 1725+123

ATel #17316; S. Rani (Michigan Technological University), G. La Mura (INAF - Astronomical Observatory of Cagliari), on behalf of the Fermi Large Area Telescope Collaboration
on 31 Jul 2025; 19:06 UT
Credential Certification: Giovanni La Mura (giovanni.lamura@inaf.it)

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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 PKS 1725+123, also known as 4FGL J1728.0+1216 (Abdollahi et al. 2022, ApJS, 260, 53), with coordinates R.A. = 262.02938 deg, Dec. = +12.26097 deg (J2000; Xu et al. 2019, ApJS, 242, 5), and redshift z = 0.568 (Nanci et al. 2022, A&A, 663, A129).

Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on July 30, 2025, with a daily averaged gamma-ray flux (E > 100 MeV) of (0.7 +/- 0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of more than 30 relative to the average flux reported in the fourth release of the Fourth Fermi-LAT catalog (4FGL-DR4, Ballet et al. 2024, arXiv:2307.12546). This is the highest LAT daily flux ever observed for this source. The corresponding photon index of 1.9 +/- 0.1 indicates a significantly harder spectrum than the 4FGL-DR4 value of 2.47 +/- 0.05 (Ballet et al. 2023, arXiv:2307.12546). The Fermi-LAT Collaboration has previously reported flaring activity from this source in ATel #17094.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. A preliminary light curve for PKS 1725+123 is available at the Fermi-LAT Light-Curve Repository. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Pietro Monti-Guarnieri (pietro.monti-guarnieri@phd.units.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.