Fermi-LAT detection of further gamma-ray brightening of the FSRQ 3C 395

ATel #18013; A. Holzmann Airasca (University of Trento and INFN Bari) and P. Monti-Guarnieri (University of Trieste and INFN Trieste), on behalf of the Fermi Large Area Telescope Collaboration
on 26 Aug 2026; 15:30 UT
Credential Certification: Giovanni La Mura (giovanni.lamura@inaf.it)

Tweet

In ATel #17968, we reported the Fermi-LAT detection of renewed activity from the flat-spectrum radio quasar 3C 395, with a daily averaged gamma-ray flux (E>100MeV) of (3.2+/-0.3) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), observed on August 15, 2026. The source is positioned at coordinates R.A. = 285.73308 deg, Decl. = +31.99492 deg (J2000; Xu et al. 2019, ApJS, 242, 5), and has a redshift value of z=0.634 (Gelderman & Whittle 1994, ApJS, 91, 491).

Preliminary analysis indicates that this source further brightened on August 25, 2026, reaching a daily averaged gamma-ray flux (E>100MeV) of (6.4 +/- 0.4) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This is a factor of 2 brighter than observed on August 15 and more than 290 times 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 1.77 +/- 0.04, indicating a harder spectrum than the 4FGL-DR4 value of 2.55 +/- 0.05 and the ATel #17968 value of 2.0 +/- 0.1. This is the highest LAT daily flux ever observed for this source. Further analysis on shorter timescales reveals that the peak 6-hr flux was (10.0+/-0.8) X 10^-6 photons cm^-2 s^-1, observed in the time interval from 06:00:00 UT to 12:00:00 UT on August 25.

The spectral hardening led to the detection of nine high-energy photons (>10 GeV) associated with the source at a confidence level p > 0.999. The highest energy event was a 31 GeV photon observed on August 25 at 09:46:56 UT. Preliminary likelihood analysis of the >10 GeV data over the period from August 21, 10:15:00 UT to August 26, 00:00:00 UT revealed a flux of (1.8 +/- 0.6) X 10^-8 photons cm^-2 s^-1, a 1000-fold increase over the 4FGL-DR4 catalog value of (1.7 +/- 0.1) X 10^-11 photons cm^-2 s^-1. The Fermi-LAT Collaboration has previously reported flaring activity from this source in ATels #14383, #17780, #17901 and #17968.

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 Marcello Giroletti (marcello.giroletti@inaf.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.