Fermi-LAT and Swift observations of flaring activity from the FSRQ PKS 0301-721
ATel #15024; G. La Mura (LIP), J. Valverde (UMBC/NASA GSFC), P. V. Van Zyl (SARAO/WITS), on behalf of the Fermi Large Area Telescope Collaboration
on 8 Nov 2021; 21:25 UT
Credential Certification: Giovanni La Mura (glamura@lip.pt)
Subjects: X-ray, Gamma Ray, AGN, Blazar, Transient
On October 12, 2021, the Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, observed increased gamma-ray activity from a source positionally consistent with the flat-spectrum radio quasar PKS 0301-721, also known as 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). Following a preliminary analysis that resulted in a daily average flux (E>100MeV) of (1.44 +/- 0.20) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only) with photon index 1.9+/-0.1, a Swift ToO request was submitted.
Swift executed two observations of the source in photon counting mode, on October 19 and October 22, accumulating, respectively, 3071.34s and 3415.07s of XRT exposure times. An X-ray source positionally consistent with PKS 0301-721 was detected in both visits. Preliminary analysis suggests that the source could be modeled with an absorbed power-law, using a fixed Galactic Hydrogen column density of 4.68 X 10^20 cm^-2 (Willingale et al. 2013, MNRAS, 431, 394). On October 19, the X-ray data in the 0.3-10keV band resulted in a flux estimate of (2.69+/-0.39) X 10^-12 erg cm^-2 s^-1, with a photon index of 1.7+/-0.2 (statistical uncertainty only). On October 22, the estimated flux had decreased to (2.14+/-0.39) X 10^-12 erg cm^-2 s^-1, with a photon index of 1.5+/-0.2. The source is listed in the 2SXPS catalogue with a flux estimate of 0.67 X 10^-12 erg cm^-2 s^-1 (Evans et al. 2020, ApJS, 247, 54).
The LAT monitoring provided simultaneous coverage of the gamma-ray evolution of this flare. On October 19, the source was detected with a daily averaged gamma-ray flux (E>100MeV) of (0.2+/-0.1) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), being 20 times brighter than the average flux reported in the fourth Fermi-LAT catalog (4FGL). On October 22, it was detected with a daily averaged gamma-ray flux (E>100MeV) of (0.4+/-0.1) X 10^-6 photons cm^-2 s^-1 (statistical uncertainty only), being 40 times brighter than the 4FGL average level.
Because Fermi normally operates in an all-sky scanning mode, regular gamma-ray monitoring of this source will continue. This source is included in the "LAT Monitored Sources" and, consequently, a preliminary estimation of the daily gamma-ray flux observed by Fermi-LAT will be publicly available ( http://fermi.gsfc.nasa.gov/ssc/data/access/lat/msl_lc/ ). We encourage multifrequency observations of this source. For this source, 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. We further acknowledge commitment of the Swift Team, Observatory Duty Scientists, and PI, who made these observations possible.