Fermi-LAT detection of renewed gamma-ray activity from the FSRQ 3C 345
ATel #16274; Denis Bernard (LLR, Ecole Polytechnique & CNRS / IN2P3), on behalf of the Fermi Large Area Telescope Collaboration
on 9 Oct 2023; 07:25 UT
Credential Certification: Denis Bernard (Denis.bernard@in2p3.fr)
Subjects: >GeV, Request for Observations, AGN, Blazar, Quasar
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 345, also known as B2 1641+39, S4 1641+39, OS 368 and 4FGL J1642.9+3948 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 250.745041 deg, Dec. = 39.810276 deg (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift z=0.5928 (Marziani et al. 1996, ApJS, 104, 37).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on October 7, 2023, with a daily averaged gamma-ray flux (E>100MeV) of (2.8 +/- 0.3) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 50 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). The corresponding photon index is 1.99 +/- 0.08, and is significantly smaller than the 4FGL value of 2.40 +/- 0.03. Previous flaring activity was reported in the ATel #15613.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. A preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT is publicly available of the "LAT Monitored Sources" page ( https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/0FGL_J1641d4p3939 ). We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is Janeth Valverde (valverde@llr.in2p3.fr).
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.
