Fermi-LAT detection of renewed gamma-ray activity from the FSRQ 3C 273

ATel #17881; P. Monti-Guarnieri (University of Trieste and INFN Trieste), F. Casaburo (INAF OAR, INFN Roma Tor Vergata and Sapienza University of Roma), on behalf of the Fermi Large Area Telescope Collaboration
on 9 Jul 2026; 07:45 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 renewed gamma-ray activity from a source positionally consistent with the flat-spectrum radio quasar 3C 273, also known as 4FGL J1229.0+0202 (Abdollahi et al. 2022, ApJS, 260, 53), with coordinates R.A. = 187.27791 deg, Dec. = +2.05239 deg (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift z=0.158 (Strauss et al. 1992, ApJS, 83, 29).

Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on July 7, 2026, with a daily averaged gamma-ray flux (E>100MeV) of (3.4+/-0.4) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of more than 10 relative to the average flux reported in the fourth data release of the fourth Fermi-LAT catalog (4FGL-DR4, Ballet et al. 2023, arXiv:2307.12546). The corresponding photon index is 2.7+/-0.1 and is consistent with the 4FGL-DR4 value of 2.69+/-0.01 within the uncertainties. The Fermi LAT Collaboration has previously reported gamma-ray flaring activity from 3C 273 in ATel #1707, #2168, #2200 and #16698.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source belongs to the "LAT Monitored Sources" and, consequently, a preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT is publicly available at 3C 273. A preliminary light curve for 3C 273 can also be accessed via the Fermi-LAT Light-Curve Repository at 4FGL J1229.0+0202. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact persons are Werner Collmar (wec@mpe.mpg.de) and Gino Tosti (tosti@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.