Fermi-LAT detection of enhanced gamma-ray activity from the FSRQ PKS 1045-18

ATel #17319; S. Rani (Michigan Technological University), G. La Mura (INAF - Astronomical Observatory of Cagliari), on behalf of the Fermi Large Area Telescope Collaboration
on 4 Aug 2025; 21:32 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 enhanced gamma-ray activity from a source positionally consistent with the flat-spectrum radio quasar (FSRQ) PKS 1045-18, also known as 4FGL J1048.0-1912 (Abdollahi et al. 2022, ApJS, 260, 53), with coordinates R.A. = 162.02759 deg, Dec. = -19.15992 deg (J2000; Xu et al. 2019, ApJS, 242, 5), and redshift z=0.595 (Stickel et al. 1993, A&AS, 97, 483).

Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on August 3, 2025, with a daily averaged gamma-ray flux (E>100MeV) 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 160 relative to the average flux reported in the fourth data release of the fourth Fermi-LAT catalogue (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-DR4 value of 2.47 +/- 0.13.

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. For this source, the Fermi-LAT contact person is Shikha Rani (rani@mtu.edu).

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.