Fermi-LAT detection of renewed gamma-ray activity from the FSRQ 3C 395

ATel #17780; F. Giacchino (USAL - Universidad de Salamanca, Spain, and INFN - Rome Tor Vergata, Sapienza University Rome), P. Monti-Guarnieri (University of Trieste and INFN Trieste) and G. La Mura (INAF - O. A. Cagliari), on behalf of the Fermi Large Area Telescope Collaboration
on 8 May 2026; 16:47 UT
Credential Certification: Federica Giacchino (federica.giacchino@roma2.infn.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 395, also known as 4C +31.52, B2 1901+31 and 4FGL J1902.8+3201 (The Fermi-LAT collaboration 2020, ApJS, 247, 33) with coordinates R.A. = 285.73308 deg, Decl. = 31.99492 deg (J2000; Xu et al. 2019, ApJS, 242, 5). 3C 395 is a known radio source showing superluminal motion (Lister et al. 2019, ApJ, 874, 43) and asymmetries between the parsec and kiloparsec scales (Lara et al. 1997, A&A, 319, 405). The redshift is z=0.634 (Gelderman & Whittle 1994, ApJS, 91, 491).

Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on May 7, 2026 with a daily averaged gamma-ray flux (E>100MeV) of (0.7 +/- 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 30 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). This is the highest daily flux ever observed for this source by the LAT. The corresponding photon index is 2.5 +/- 0.2, consistent with the 4FGL-DR4 value of 2.55 +/- 0.05. The Fermi-LAT Collaboration has previously reported flaring activity from this source in ATel #14383.

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.