A renewed gamma-ray flare from the Gigahertz-peaked Spectrum radio source OS 300
ATel #14422; Giacomo Principe (University of Trieste and INFN-Trieste, INAF - Istituto di Radioastronomia, Bologna) on behalf of the Fermi-LAT Collaboration
on 23 Feb 2021; 22:47 UT
Credential Certification: Simone Garrappa (simone.garrappa@gmail.com)
Subjects: Gamma Ray, Request for Observations, AGN, Blazar
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed renewed, bright gamma-ray emission from a source positionally consistent with the radio source OS 300 (B1600+335, 4C +33.38), also known as 4FGL J1602.1+3324 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 240.5302642 deg, Decl. = +33.4480756 deg (J2000; Johnston et al. 1995, AJ, 110, 880). OS 300 is best known as a gigahertz-peaked spectrum (GPS) radio source (Snellen et al. 2000 MNRAS 319, 445) with complex radio morphology (Tremblay et al. 2010 ApJ 712, 159). Its redshift was estimated photometrically as z = 1.1 (Snellen et al. 2000 MNRAS 319, 445) and is thus tentative (see Dallacasa et al. 2013 MNRAS 433, 147).
Preliminary analysis indicates that this source was in a flaring state on 2021 February 22, with a daily averaged gamma-ray flux (E>100MeV) of (0.50+/-0.15) X 10^-6 photons cm^-2 s^-1 (uncertainties are statistical only), and a peak 6-hr flux of (1.0+/-0.4) X 10^-6 photons cm^-2 s^-1 from 00:00-06:00 UTC. The former corresponds to a flux increase of a factor of 110 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). This is the second flaring episode of this source, with flux values similar to those reported on 2020 August 10 (ATel #13931). The corresponding daily photon index is 2.3+/-0.2, and is compatible with the 4FGL value.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source has been added to the "LAT Monitored Sources" and consequently, a preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT will be publicly available (https://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/source/OS_300). We encourage multifrequency observations of this source. For this source, the Fermi-LAT contact person is C.C. Cheung (teddy.cheung@nrl.navy.mil).
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.
