Swift follow-up observations of the gamma-ray flaring blazar PKS 1830-211, a gravitationally lensed system
ATel #12696; S. Buson (Univ. of Wuerzburg, DE; UMBC, USA), A. Gokus (Univ. of Wuerzburg, Remeis Observatory Bamberg, DE), J. Wilms (Remeis Observatory Bamberg, DE), C. C. Cheung (NRL, USA), S. Ciprini (INFN Roma Tor Vergata, ASI, IT), M. Nowak (Washington Univ., St. Louis, USA)
on 26 Apr 2019; 16:11 UT
Credential Certification: Sara Buson (sara.buson@gmail.com)
Subjects: X-ray, Gamma Ray, Request for Observations, AGN, Blazar, Gravitational Lensing
Referred to by ATel #: 12737
PKS 1830-211 is a flat-spectrum-radio-quasar at z=2.507 (Lindman et al. 1999 ApJ 514, 57), gravitationally lensed by a galaxy at z=0.886 (Wiklind & Combes 1996 Nature 379, 139). The blazar has been undergoing major enhanced gamma-ray activity since the beginning of March 2019 (ATel #12541, ATel #12601, ATel #12659).
We have obtained twenty Swift target of opportunity observations that have been performed since 3 March 2019 with roughly a three-day cadence. Swift/XRT data were taken in Photon Counting mode for a total exposure of about 2 ksec per visit. For a simultaneous fit (0.2 - 10 keV) of an absorbed power law using the complete sampling of XRT data since March, we find a photon index of 1.3 +/- 0.1 and a HI column density of N_H = 1.2 x 10^22 cm^-2. The average observed 0.3-10 keV flux is (2.0+/- 0.2) x10^-11 erg cm^-2 s^-1, slightly higher than what was found in previous XRT observations (e.g., Abdo et al 2015 ApJ 799, 143).
The estimated gravitational delay for this system is 26 days (+4/-5 days; Lovell et al, 1998 ApJ 508, 51). The Swift observations span a total of 48 days, thus approximately two delay cycles. Visual inspection of the light curve suggests a delayed variability pattern on the 26 day timescale, but a quantitative analysis is ongoing. Further continuous Swift observations will help accessing the statistical significance of this pattern.
In consideration of the ongoing activity of this source, confirmed also by the Swift observations, we strongly encourage further multiwavelength observations. We would like to thank the Swift Team for making these observations possible, in particular K. L. Page and A. Tohuvavohu as Swift Observatory Duty Scientists.
