Fermi-LAT detection of renewed gamma-ray activity from the FSRQ PKS 0736+01
ATel #17509; P. Monti-Guarnieri (University of Trieste and INFN Trieste), on behalf of the Fermi Large Area Telescope Collaboration
on 29 Nov 2025; 16:05 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 renewed gamma-ray activity from a source positionally consistent with the flat-spectrum radio quasar PKS 0736+01, also known as 4FGL J0739.2+0137 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 114.82514 deg, Dec = 1.61795 deg (J2000, Johnston et al. 1995, AJ, 110, 880), and redshift 0.18941 (Ho & Kim, 2009, ApJS, 184, 398).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on November 28, 2025, with a daily averaged gamma-ray flux (E>100MeV) of (2.3 +/- 0.3) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 20 relative to the average flux reported in the fourth release of the fourth Fermi-LAT catalog (4FGL-DR4, Ballet, J. et al. 2023, arXiv:2307.12546). The corresponding photon index is 1.9 +/- 0.1, indicating a significantly harder spectrum than the 4FGL-DR4 value of 2.39 +/- 0.01. The Fermi-LAT Collaboration has previously reported flaring activity from this source in ATels #16179 and #6731 and in GCNs 1558190650 and 1558277046. The spectral hardening led to the detection of two high-energy (E>10GeV) photons associated with the source at a confidence level p > 0.999. The highest energy event was a 20 GeV photon observed at 04:29:42 UT.
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 0736+01 can be accessed via the Fermi-LAT Light-Curve Repository at 4FGL J0739.2+0137. A preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT is also publicly available on the LAT Monitored Source page at PKS_0736+01. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Filippo D'Ammando (filippo.dammando@fisica.unipg.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.
