Fermi-LAT detection of renewed gamma-ray activity from the FSRQ 4C +10.45

ATel #17924; Adithiya Dinesh (Universidad Complutense de Madrid), on behalf of the Fermi Large Area Telescope Collaboration
on 24 Jul 2026; 18:25 UT
Credential Certification: Adithiya Dinesh (adinesh@ucm.es)

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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 4C +10.45, also known as 4FGL J1608.7+1029 (Abdollahi et al. 2022, ApJS, 260, 53), with coordinates R.A. = 242.19251 deg, Decl. = +10.48549 deg (J2000; Le Bail et al. 2016, AJ, 151, 79L), and redshift z=1.233 (SDSS-DR13, Albareti et al. 2017, ApJS, 233, 25).

Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on July 23, 2026, with a daily averaged gamma-ray flux (E>100MeV) of (0.8 +/- 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 20 relative to the average flux reported in the fourth data release of the Fourth Fermi-LAT catalog (4FGL-DR4, Ballet et al. 2024, arXiv:2307.12546). The corresponding photon index is 2.4 +/- 0.2, and is consistent with the 4FGL-DR4 value of 2.53 +/- 0.03 within the uncertainties. The Fermi-LAT Collaboration has previously reported a flare of this source in ATels #16889 and #17206. Enhanced optical activity from the source was also reported in ATel #17916 on July 21, 2026.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. A preliminary light curve for 4C +10.45 can be accessed via the Fermi-LAT Light-Curve Repository and via the Monitored Source List. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Adithiya Dinesh (adinesh@ucm.es).

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.