Fermi-LAT detection of renewed gamma-ray activity from the high-redshift FSRQ PKS 0601-70
ATel #17429; S. Lopez-Perez (LLR, Ecole Polytechnique & CNRS/IN2P3), A. Holzmann Airasca (University of Trento & INFN Bari), and F. Casaburo (INAF-OAR & INFN Roma Tor Vergata & University of Roma La Sapienza), on behalf of the Fermi Large Area Telescope Collaboration
on 2 Oct 2025; 19:08 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 0601-70, also known as 4FGL J0601.1-7035 (Abdollahi et al. 2022, ApJS, 260, 53), with coordinates R.A. = 90.29717 deg, Dec. = -70.60239 deg (J2000; Healey et al. 2007, ApJS, 171, 61), and redshift z=2.409 (Shaw et al. 2012, ApJ, 748, 49).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on October 1, 2025, with a daily averaged gamma-ray flux (E>100MeV) of (1.5+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 40 relative to the average flux reported in the fourth data release of the 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 2.1+/-0.1, indicating a harder spectrum than the 4FGL-DR4 value of 2.37 +/- 0.02. The Fermi-LAT Collaboration has previously reported enhanced activity from this source in ATels #13506 and #17359.
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 0601â70 can be accessed via the Fermi-LAT Light-Curve Repository at 4FGL J0601.1-7035. This source will be added to the list of Fermi-LAT daily monitored sources. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is I. Mereu (isabella.mereu@pg.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.
