Fermi-LAT detection of enhanced gamma-ray activity from the FSRQ PKS 1958-179.
ATel #17740; P. van Zyl (South African Radio Astronomy Observatory, SARAO), on behalf of the Fermi Large Area Telescope Collaboration
on 5 Apr 2026; 19:05 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Pfesesani van Zyl (pfesi24@gmail.com)
Subjects: Gamma Ray, >GeV, AGN
The Large Area Telescope (LAT), one of the two instruments onboard the Fermi Gamma-ray Space Telescope, has observed enhanced gamma-ray activity from a source positionally consistent with the flat spectrum radio quasar PKS 1958-179, also known as 4FGL J2000.9-1748 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 300.23788 deg, Dec. = -17.81602 deg (J2000; Le Bail et al. 2016, AJ, 151, 3), and redshift z= 0.652 (Drinkwater et al., 1997, MNRAS, 284, 85).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on April 3rd, 2026, with a daily averaged gamma-ray flux (E>100MeV) of (0.6+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of about 20 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). The corresponding photon index is 1.9+/-0.2, which indicates a harder spectrum than the 4FGL-DR4 value of 2.24+/-0.03. This is the highest LAT daily flux ever observed for this source.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. A preliminary light curve for this source can be accessed via the Fermi-LAT Light Curve Repository at 4FGL J2000.9-1748. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Pfesi van Zyl (pfesi24@gmail.com).
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.
