Fermi-LAT detection of renewed gamma-ray activity from the FSRQ OP 313
ATel #16940; Omer Faruk Coban (Institute of Space Sciences, ICE-CSIC), Giovanni La Mura (INAF - O. A. Cagliari), Pietro Monti-Guarnieri (University of Trieste and INFN Trieste), Chiara Bartolini (University of Trento and INFN Bari), on behalf of the Fermi Large Area Telescope Collaboration
on 11 Dec 2024; 18:31 UT
Credential Certification: Giovanni La Mura (glamura@lip.pt)
Subjects: Gamma Ray, >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 (FSRQ) OP 313 (B2 1308+32), also known as 4FGL J1310.5+3221 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 197.61943 deg, Decl. = +32.34549 deg (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift z=0.997 (Schneider et al. 2010, AJ, 139, 2360).
Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on December 10, 2024, with a daily averaged gamma-ray flux (E>100MeV) of (1.3+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 25 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). The corresponding photon index is 1.6+/-0.1, indicating a significantly harder spectrum than the 4FGL value of 2.23+/-0.01. This is the hardest photon index observed to date for this source. The spectral hardening led to the detection of six high-energy photons associated with the source at a confidence level p > 0.999. The highest energy event was an 18 GeV photon observed on December 10 at 21:47:59 UT. Further likelihood analysis dedicated to the HE domain over the period from December 04, 10:13:15.000 UTC to December 11, 05:47:50.000 UTC, revealed a flux above 10 GeV of (8.78 +/- 2.94) X 10^-9 photons cm^-2 s^-1, a 73-fold increase over the 3FHL catalog value of (1.21 +/- 0.21) X 10^-10 photons cm^-2 s^-1. The Fermi-LAT Collaboration has previously reported flaring activity from this source in ATels #6068, #15483, #16356 and #16497.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. A preliminary light curve for OP 313 can be accessed via the Fermi-LAT Light-Curve Repository at https://fermi.gsfc.nasa.gov/ssc/data/access/lat/LightCurveRepository/source.html?source_name=4FGL_J1310.5+3221. We encourage multifrequency observations of this source. For OP 313, the Fermi-LAT contact person is Sara Buson (sara.buson at astro.uni-wuerzburg.de).
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.
