Fermi-LAT detection of enhanced gamma-ray activity from the FSRQ 4C +27.50
ATel #15549; G. La Mura (LIP, Portugal), on behalf of the Fermi Large Area Telescope Collaboration
on 14 Aug 2022; 06:02 UT
Credential Certification: Giovanni La Mura (glamura@lip.pt)
Subjects: Gamma Ray, 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 enhanced gamma-ray activity from a source positionally consistent with the flat-spectrum radio quasar 4C +27.50, also known as 4FGL J2321.9+2734 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 350.49943 deg, Decl. = +27.54623 deg (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift z = 1.253 (Stickel & Kuehr 1992, A&A, 264, 68).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on August 12, 2022, with a daily averaged gamma-ray flux (E>100MeV) of (0.6+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 40 relative to the average flux reported in the third release of the fourth Fermi-LAT catalog (4FGL-DR3, Abdollahi et al. 2022, ApJS, 260, 53). This is the highest LAT daily flux ever observed for this source. The corresponding photon index is 2.42+/-0.24, and is consistent with the 4FGL-DR3 value of 2.22+/-0.04 within the uncertainties.
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 Giovanni La Mura (glamura@lip.pt).
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.
