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ATEL # 3025; J. A. Kennea (PSU), M. A. P. Torres (SRON/CfA), D. Steeghs (U Warwick), J. Homan (MIT) and J. M. Miller (Michigan)
on 11 Nov 2010; 17:39 UT
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Password Certification: Jamie A. Kennea (firstname.lastname@example.org)
Subjects: X-ray, Transients
Swift performed a target of opportunity observation of 4U 1137-65, reported to be in outburst by MAXI (Nakajima et al., ATEL #3021), starting 23:13UT on November 10th, 2010 for 1ks, with XRT in Photon Counting mode. We detect a bright X-ray source at the following position: RA, Dec (J2000) = 174.8724, -65.3978, which is equivalent to:RA(J2000) = 11h 39m 29.4s
with an error circle of 3.6 arc-min radius (90% confidence). This position lies 1.4 arc-sec from the optical position of GT Mus (AKA 4U 1137-65, HD 101379), and 6.2 arc-min from the center of the MAXI error circle, unambiguously identifying the Swift detected X-ray source as both the MAXI transient and GT Mus.
In the short observation the source is bright and steady, with an XRT count rate of ~26 XRT counts/s (~37 mCrab). The spectra is well fit by an absorbed power-law model with N_H = 1.4 x 1021 cm-2 and a photon index of 2.0 +/- 0.1. The flux, uncorrected for absorption, is 10-9 erg/s/cm^2 (0.3-10 keV), which when converted into ROSAT counts, is approximately 10 times brighter than its measured brightness in the ROSAT All Sky-Survey, confirming that GT Mus is currently in X-ray outburst, as proposed by the Nakajima et al. (ATEL #3021).
This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester (Evans et al. 2009, MNRAS, 397, 1177).