Fermi-LAT detection of enhanced gamma-ray activity from the FSRQ 3C 345

ATel #15613; Janeth Valverde (UMBC/NASA GSFC), Simone Garrappa (DESY-Zeuthen), on behalf of the Fermi Large Area Telescope Collaboration
on 12 Sep 2022; 14:35 UT
Credential Certification: Janeth Valverde (valverde@llr.in2p3.fr)

Tweet

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 3C 345 (also known as B2 1641+39, S4 1641+39, OS 368, 3FGL J1642.9+3950), with VLBI coordinates (J2000.0), R.A.: 250.745041 deg, Dec.: 39.810276 deg (Johnston et al. 1995, AJ, 110, 880)., and redshift z=0.5928 (Marziani et al. 1996, ApJS, 104, 37). 3C 345 is characterised by a strong and extended radio and X-ray jet with an extended radio structure observable from sub-pc to kpc scales, and shows structural and flux variability on parsec scale (e.g. Lister et al. 2013, AJ, 146, 120).

Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on 2022 September 10, with a daily averaged gamma-ray flux (E>100MeV) of (3.9+/-0.3) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 60 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+/-0.1, and is significantly harder than the 4FGL value of 2.40+/-0.03. This is the fourth time that the Fermi-LAT Collaboration has announced flaring GeV gamma-ray behavior from a source spatially consistent with 3C 345 after ATels #15313, #10453 and #2226.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. Preliminary light curves can be accessed via the Monitored Source List at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/0FGL_J1641d4p3939, and via the Fermi-LAT Light-Curve Repository at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/LightCurveRepository/source.html?source_name=4FGL_J1642.9+3948. We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is F. Schinzel (fschinze@nrao.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.