Fermi-LAT detection of enhanced gamma-ray activity from the Giga-Hertz Peaked Spectrum radio source OS 300
ATel #15126; G. La Mura (LIP, Portugal), on behalf of the Fermi Large Area Telescope Collaboration
on 17 Dec 2021; 23:10 UT
Credential Certification: Giovanni La Mura (glamura@lip.pt)
Subjects: Gamma Ray, >GeV, Request for Observations, AGN, Transient
Referred to by ATel #: 15146
The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed remarkably enhanced 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. = 240.530 deg, Decl. = +33.448 deg (J2000; Johnston et al. 1995, AJ, 110, 880). OS 300 is best known as a Giga-Hertz 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 December 16, with a daily averaged gamma-ray flux (E>100MeV) of (0.94+/-0.18) X 10^-6 photons cm^-2 s^-1 (uncertainties are statistical only), and a peak 6-hr flux of (1.6+/-0.5) X 10^-6 photons cm^-2 s^-1 from 12:00-18:00 UTC. The former corresponds to a flux increase of a factor of 200 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). This is the third flaring episode associated with this source and the highest flux state ever observed by LAT (see ATels #13931, #14422). The daily photon index is 2.0+/-0.1, smaller than the 4FGL average value of 2.2+/-0.1.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source is part of 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.
