Fermi-LAT detection of enhanced gamma-ray activity from the FSRQ PKS 1725+123
ATel #17624; S. Rani (Michigan Technological University), T. Lewis (Michigan Technological University), G. La Mura (INAF - Astronomical Observatory of Cagliari), P. Monti-Guarnieri (University of Trieste and INFN Trieste) on behalf of the Fermi Large Area Telescope Collaboration
on 23 Jan 2026; 20:45 UT
Credential Certification: Giovanni La Mura (giovanni.lamura@inaf.it)
Subjects: Gamma Ray, >GeV, Request for Observations, Blazar, Quasar
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 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 = 0.586 (Shaw et al. 2013, ApJ, 764, 135).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on January 22, 2026, with a daily averaged gamma-ray flux (E>100MeV) of (1.1+/-0.2) e-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of more than 60 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). The corresponding photon index is 1.8+/-0.1, indicating a significantly harder spectrum than the 4FGL-DR4 value of 2.47+/-0.05. Two high-energy photons with energies of 12 GeV and 15 GeV are associated with the source with probabilities p > 0.99. The Fermi-LAT Collaboration has previously reported flaring activity from this source in ATels #17370, #17094 and #17316.
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. A preliminary light curve for PKS 1725+123 is available via the Fermi-LAT Light-Curve Repository at 4FGL J1728.0+1216. 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.
