Fermi-LAT detection of enhanced gamma-ray activity from the FSRQ PKS 0907-023
ATel #17133; Adithiya Dinesh (Universidad Complutense de Madrid), Janeth Valverde (Marquette University) , on behalf of the Fermi Large Area Telescope Collaboration
on 5 Apr 2025; 23:54 UT
Credential Certification: Janeth Valverde (valverde@llr.in2p3.fr)
Subjects: Gamma Ray, >GeV, VHE, AGN, 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 0907-023, also known as 4FGL J0909.7-0230 (4FGL; The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 137.43718 deg, Dec. = -2.52510 deg (J2000; Hunt et al. 2021, AJ, 162, 121), and redshift z=0.957 (Xiao et al. 2022, ApJ, 936, 146).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on April 4, 2025, with a daily averaged gamma-ray flux (E>100MeV) of (0.5+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 16 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). This is the highest LAT daily flux ever observed for this source. The corresponding photon index is 1.9+/-0.2, indicating a significantly harder state than the 4FGL value of 2.29+/-0.02. The hard spectral state led to the observation of a high-energy photon of E = 15 GeV, associated with the source with a probability p > 0.999.
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 0907-023 can be accessed via the Fermi-LAT Light-Curve Repository at 4FGL J0909.7-0230. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact persons are Adithiya Dinesh (adinesh@ucm.es) and Janeth Valverde (janeth@umbc.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.
