Fermi-LAT detection of enhanced gamma-ray activity from the FSRQ OP 313 (B2 1308+32)

ATel #15483; S. Garrappa (DESY-Zeuthen) on behalf of the Fermi-LAT collaboration
on 29 Jun 2022; 07:36 UT
Credential Certification: Simone Garrappa (simone.garrappa@gmail.com)

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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 OP 313 (B2 1308+32), also known as 4FGL J1310.5+3221 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 197.619432 deg, Decl. = +32.345495 deg (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift z=0.997 (Schneider et al. 2010, AJ, 139, 2360).

The source OP 313 was recently reported by several observatories in an unprecedented optical outburst, and is currently observed at the brightest optical flux levels ever measured for this source (see ATel #15480, #15476, #15474, #15459, #15447).

Preliminary analysis indicates that this source was in an elevated gamma-ray emission state on June 27, 2022, with a daily averaged gamma-ray flux (E>100MeV) of (1.1+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of ~20 relative to the average flux reported in the fourth Fermi-LAT catalog (4FGL). This is the highest LAT daily flux ever observed for this source. The corresponding photon index is 1.98+/-0.14, and is significantly smaller than the 4FGL value of 2.34+/-0.02.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. Preliminary light curves 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 this source, the Fermi-LAT contact person is Sara Buson (sara.buson at 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.