Improved position and possible optical counterpart for the new X-ray transient Swift J1658.2-4242
ATel #11307; I. A. Mereminskiy, S. A. Grebenev (Space Research Institute, Moscow)
on 16 Feb 2018; 16:33 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Ilya Mereminskiy (i.a.mereminskiy@gmail.com)
Subjects: X-ray, Transient
A follow-up pointing observation (ObsId:00810300991, 2.8 ks) of the recently discovered X-ray transient Swift J1658.2-4242 (GCN #22416, #22417) has been performed by Swift-XRT on MJD 58165.3 in PC mode. It allowed us to improve the source position using UVOT data to reduce the systematic errors in telescope pointing (see Goad et al. A&A, 476, 1401, 2007; Evans et al. MNRAS, 397, 1177, 2009): R.A. = 254.55268, Dec. = -42.69847 (=16h 58m 12.64s, -42o 41' 54.5'', epoch 2000.0). The error radius is 1.6'' at 90% confidence. There is a known infrared source VVV J165812.62-424154.78 with Ks magnitude of 15.25 located only 0.4'' off this position.
The spectrum measured with XRT can be described by a strongly absorbed power-law with a photon index of 1.2+/-0.3 and NH = 1.5 x 10^{23} cm^{-2}. The source flux was about 7.2 (+/-0.6) x 10^{-10} erg s^{-1} cm^{-2} in the 0.3-10 keV band that corresponds to the unabsorbed luminosity 1.8 x 10^{37} erg/s at an assumed distance of 10 kpc. The hardness of the spectrum is consistent with that based on INTEGRAL data (ATEL #11306).
This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester.
