Swift-XRT observations of the blazar PKS 0735+178 in a flaring state
ATel #15102; Marcos Santander (U. Alabama), Sara Buson (U. Wurzburg)
on 10 Dec 2021; 22:09 UT
Credential Certification: Marcos Santander (jmsantander@ua.edu)
Subjects: X-ray, Neutrinos, Request for Observations, AGN, Blazar
The blazar PKS 0735+178 was recently detected in a high flux state both in the optical band by MASTER (ATel #15098) and in the GeV gamma-ray band by Fermi-LAT (ATel #15099) during follow-up observations of the region around the IceCube neutrino event IC211208A (GCN #31191). PKS 0735+178 is located 2.2 deg away from the best-fit neutrino position, although outside the 90% uncertainty region reported by IceCube for this event.
Target of opportunity observations of PKS 0735+178 were performed with the The Neil Gehrels Swift Observatory on 2021 December 10 UT for a total XRT exposure of approximately 2.2 ksec in photon counting mode.
The data were analyzed using the Leicester XRT analysis pipeline (Evans et al. 2009, MNRAS, 397, 1177) using an absorbed power-law model, which results in an intrinsic flux in the 0.3-10 keV band of (8.4 +/- 1.3) x 10^-12 erg cm^-2 s^-1 with a photon index of 2.6 +/- 0.2 for a Galactic column density of 4.5 x 10^20 cm^-2 (Willingdale et al. 2013). This flux level is about a factor of ~6 higher than that observed by Swift XRT on the same source in previous observations taken in 2009-2011 (https://www.swift.psu.edu/monitoring/source.php?source=0735+178) and is the highest X-ray flux observed for this source during the Swift mission. This flux increase is of similar amplitude as that reported by Fermi-LAT in the GeV band. Additional Swift observations are planned during the coming week. We encourage multiwavelength observations of this source.
We wish to thank the Swift Team for making these observations possible, in particular B. Sbarufatti as the Swift Observatory Duty Scientist.