Swift/XRT discovers a new X-ray transient near the Galactic center: Swift J174535.5-285921
ATel #3472; N. Degenaar, R. Wijnands (UvA), J. A. Kennea (PSU) and N. Gehrels (GSFC)
on 5 Jul 2011; 15:18 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Nathalie Degenaar (degenaar@uva.nl)
Subjects: X-ray, Binary, Black Hole, Neutron Star, Transient
Monitoring observations of the Galactic center performed with Swift's X-ray Telescope (XRT) reveal a transient X-ray source located ~1.3' NE of Sgr A*. This object is clearly detected during a 1.0-ks photon counting (PC) mode observation obtained on 2011 July 3, but not in the proceeding 1.0-ks observation performed on 2011 June 30, nor in any previous XRT observations of this region carried out between 2006 and 2011 (Degenaar & Wijnands 2009, A&A 495, 547; 2010, A&A 524, 69). There is no X-ray transient known at this position, although the Swift error circle contains several weak X-ray sources from the Chandra catalogue of Muno et al. (2009, ApJS 181, 110).
The XRT coordinates of the new X-ray transient are R.A. = 17:45:36.00 and Dec. = -28:59:27.9, with an uncertainty of 3.8". The XRT-UVOT enhanced position is:
R.A. (J2000) = 17:45:35.50 (266.39793 deg)
DEC (J2000) = -28:59:21.5 (-28.98931 deg)
with a 90% confidence error of 3.3". Position enhancement is described by Goad et al. (2007, A&A 476, 1401) and Evans et al. (2009, MNRAS 397, 1177).
The new X-ray source, which we designate Swift J174535.5-285921, is detected at an XRT count rate of ~0.05 counts s-1. The PC-mode spectrum can be described by a simple absorbed powerlaw model with a photon index of 2.1 +/- 1.0 and a hydrogen column density of (9.0 +/- 5.0)E22 cm-2. The resulting absorbed and unabsorbed fluxes in the 2-10 keV energy range are ~9.6E-12 and 1.9E-11 erg cm-2 s-1, respectively. For a distance of 8 kpc, the latter would translate into a 2-10 keV luminosity of ~1.5E35 erg s-1.
Swift monitoring observations of the Galactic center are continuing. The reported analysis was performed utilizing the tools described in Evans et al. (2009).
