Fermi-LAT detection of enhanced/renewed gamma-ray activity from the FSRQ blazars PKS 0301-721 and PKS 0920-39

ATel #14918; P. V. Van Zyl (South African Radio Astronomy Observatory (SARAO)), J. Valverde (UMBC/NASA GSFC), on behalf of the Fermi Large Area Telescope Collaboration
on 14 Sep 2021; 19:33 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 increased gamma-ray flux from a source positionally consistent with the flat spectrum radio quasar PKS 0301-721 (4FGL J0301.6-7155; The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 45.410 deg, Decl. = -71.943 deg (J2000; Li & Jin 1996, A&AS, 120, 201), and redshift z=0.823 (Titov et al. 2013, AJ, 146, 10).

Preliminary analysis indicates that on 2021 September 10, PKS 0301-721 was in an active state reaching a daily averaged gamma-ray flux (E>100 MeV) of (1.0+/-0.2) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), about 100 times greater than its ten-year average flux reported in the fourth Fermi-LAT source catalog data release 2 (4FGL-DR2; Ballet et al., arXiv:2005.11208). The corresponding daily averaged spectral photon index (E>100 MeV) of 2.1+/-0.1 (statistical uncertainty only) is smaller than the 4FGL-DR2 catalog value of 2.5+/-0.1. The peak flux is detected in the 4th 6-hour run interval of September 10 with a 6-hour averaged gamma-ray flux (E>100 MeV) of (1.2+/-0.3) X 10^-6 photons cm^-2 s^-1, and corresponding spectral photon index (E>100 MeV) of 2.0+/-0.2. GeV gamma-ray activity of PKS 0301-721 has been previously announced once in 2020, by the Fermi LAT Collaboration (ATel#14293).

Also on September 10, the LAT has observed enhanced gamma-ray flaring activity from a source positionally consistent with the flat spectrum radio quasar PKS 0920-39 (4FGL J0922.7-3959; The Fermi-LAT collaboration 2020, ApJS, 247, 33), with coordinates R.A. = 140.55 deg and Decl. = -39.70 deg (J2000, Johnston et al. 1995, AJ, 110, 880), and redshift z=0.591 (Hewitt and Burbidge 1989, ApJS, 69, 1). Preliminary analysis indicates that on 2021 September 10, PKS 0920-39 was in a flaring state with a daily averaged gamma-ray flux (E>100MeV) of (1.0+/-0.2) X 10^-6 photons cm^-2 s^-1, which corresponds to a flux increase factor of 50 times the ten-year average flux reported in the 4FGL-DR2 catalog of 2.1 X 10^-8 photons cm^-2 s^-1. This daily flux has been previously observed for this source in ATel#5326 and we suspect this might be a renewed flare. The corresponding photon index is 2.4+/-0.2, and is moderately smaller than the 4FGL value of 2.6+/-0.1. The peak flux is detected in the 3rd 6-hour interval of September 10 between 12:00 and 18:00 UT with a 6-hour averaged gamma-ray flux (E>100 MeV) of (2.1+/-1.0) X 10^-6 photons cm^-2 s^-1, and corresponding spectral photon index (E>100 MeV) of 2.6+/-0.6.

PKS 0920-39 is included in the list of publicly monitored sources found at the Fermi Science Support Center. PKS 0301-721 is still in the process of being added to the monitored sources list. Because Fermi operates in an all-sky scanning mode, regular gamma-ray monitoring of these sources will continue. In consideration of the ongoing activity of this source, we encourage multiwavelength observations. For these sources, the Fermi LAT contact people are Pfesi Van Zyl (pfesesani at hartrao.ac.za) and Janeth Valverde (valverde at llr.in2p3.fr).

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.