Swift/XRT detection of an active X-ray transient near the Galactic center
ATel #5074; N. Degenaar (Michigan), R. Wijnands (UvA), M. T. Reynolds, J. M. Miller (Michigan), J. A. Kennea (PSU) and N. Gehrels (GSFC), on behalf of a larger collaboration
on 20 May 2013; 08:13 UT
Credential Certification: Rudy Wijnands (rudy@space.mit.edu)
Subjects: X-ray, Transient
Referred to by ATel #: 5095
Daily monitoring observations of the Galactic center performed with the Swift/XRT (Atel #5006; see link below) reveal that in addition to the new magnetar SGR J1745-29 (Atels #5009,#5011, #5020, #5032, #5037, #5046, #5053; Kennea et al. 2013; Mori et al. 2013) a transient X-ray source located ~20" north of Sgr A* is currently active. This object is clearly detected during ~1.0 ks PC mode observations obtained on 2013 May 15, 16, 18 and 19, at count rates of ~(1.5-5.0)E-2 counts/s. The intensity at the source position is consistent with the local background level (~7E-3 counts/s) during other observations performed earlier this year. This source is very likely the same transient that was detected with NuSTAR on 2013 May 18-19 (Atel # 5073).
Summing the Swift/XRT data of May 15-19 (Obs IDs 91736035-38) shows that the X-ray spectrum can be characterized by an absorbed power-law model with NH~1.9E23 cm-2 and a photon index of ~2.4. The resulting absorbed (unabsorbed) 2-10 keV flux is 9.0E-12 (2.3E-11) erg/cm2/s. Assuming a distance of 8 kpc, this translates into a 2-10 keV luminosity of 1.8E35 erg/s.
Using the tool xrtcentroid, we determine a position of R.A. = 17:45:39.86 and Dec. = -29:00:02.3 (J2000), with an uncertainty of 3.6" (90% confidence). This position is ~4.5" from that of the known recurrent X-ray transient CXOGC J174540.1-290005, which was active in 2003 and 2006 (Muno et al. 2005; Degenaar & Wijnands 2009; see also Atel #5073). The spectral parameters and intensity inferred for the currently active transient are comparable to that observed with Swift/XRT in 2006 for CXOGC J174540.1-290005 (Degenaar & Wijnands 2009). We therefore consider it likely that we have detected renewed activity of this transient. Its 2006 outburst had a duration of ~2 weeks.
We encourage follow-up observation at different wavelengths to determine the nature of this transient X-ray source.
Swift Monitoring Campaign Website: http://www.swift-sgra.com/
References:
Degenaar & Wijnands 2009, A&A 495, 547
Kennea et al. 2013, accepted to ApJ letters, arXiv:1305.2128
Mori et al. 2013, accepted to ApJ letters, arXiv:1305.1945
Muno et al. 2005, ApJ 622, L113
