Fermi-LAT detection of enhanced gamma-ray activity from the FSRQ blazars PKS 0308-611 and OI 275

ATel #15007; J. Valverde (UMBC/NASA GSFC), P. V. Van Zyl (South African Radio Astronomy Observatory (SARAO)), Stefano Ciprini (INFN Roma Tor Vergata, & ASI Space Science Data Center, Rome, Italy), on behalf of the Fermi Large Area Telescope Collaboration
on 28 Oct 2021; 03:45 UT
Credential Certification: Janeth Valverde (valverde@llr.in2p3.fr)

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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 PKS 0308-611, also known as 4FGL J0309.9-6058 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 47.484 deg, Decl. = -60.977 deg (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift z=1.48 (Gattano et al. 2018, A&A, 618, A80).

Preliminary analysis indicates that this source has been in an elevated gamma-ray emission state on 2021 October 24 and 25, reaching on October 25, 2021, a daily averaged gamma-ray flux (E>100MeV) of (0.6+/-0.1) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 11 relative to the average flux reported in the fourth Fermi-LAT catalog data release 2 (4FGL-DR2; Ballet et al., arXiv:2005.11208). This is the highest LAT daily flux ever observed for this source. The corresponding photon index is 2.2+/-0.2, and is consistent with the 4FGL-DR2 value of 2.49+/-0.02 within the uncertainties.

On October 23, the LAT observed enhanced gamma-ray activity from a source positionally consistent with the flat-spectrum radio quasar OI 275, also known as 4FGL J0748.6+2400 (The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 117.150 deg, Decl. = 24.007deg (J2000; Johnston et al. 1995, AJ, 110, 880), and redshift z=0.41 (Schneider et al. 2010, AJ, 139, 2360). Preliminary analysis indicates that on 2021 October 23, OI 275 was in a flaring state with a daily averaged gamma-ray flux (E>100MeV) of (0.3+/-0.1) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only). This corresponds to a flux increase of a factor of 24 relative to the average flux reported in the 4FGL-DR2. This is the highest LAT daily flux ever observed for this source. The corresponding photon index is 2.1+/-0.3, and is consistent with the 4FGL-DR2 value of 2.34+/-0.06 within the uncertainties.

Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of these sources will continue. We encourage multifrequency observations of these sources. For these sources, the Fermi-LAT contact people are Janeth Valverde (valverde at llr.in2p3.fr) and Pfesi Van Zyl (pfesesani at hartrao.ac.za).

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.