Swift J1753.7-2544: Swift localization of a bright X-ray counterpart

ATel #4789; H. A. Krimm (CRESST/GSFC/USRA), J. A. Kennea (PSU), S. T. Holland (CRESST/GSFC/USRA), S. D. Barthelmy (GSFC), W. Baumgartner (CRESST/GSFC/UMBC), J. Cummings (CRESST/GSFC/UMBC), N. Gehrels (GSFC), C. B. Markwardt (GSFC), D. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU/GSFC), J. Tueller (GSFC), T. Ukwatta (MSU)
on 5 Feb 2013; 22:31 UT
Credential Certification: Hans A. Krimm (Hans.Krimm@nasa.gov)

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We report on Swift follow-up observations of Swift J1753.7-2544 (ATel #4769) with the Swift X-ray Telescope (XRT). On February 4, 2013 (MJD 56327) at 11:15 UT Swift began a target of opportunity observation of the BAT error circle of Swift J1753.7-2544. The XRT was configured into Photon Counting (PC) mode in order to obtain an accurate localization. We detect a very bright, uncatalogued X-ray source at the following location: RA/Dec (J2000) = 268.41615, -25.75355, which is equivalent to:

RA(J2000) = 17h 53m 39.88s
Dec(J2000) = -25d 45' 12''.8,

with an estimated uncertainty of 2.3 arc-seconds radius (90% confidence). This position lies 1.0 arc-minutes from the Swift/BAT position reported by Krimm et al. (ATEL #4769), well within the BAT error circle.

The pile-up corrected PC mode spectrum can be well fitted by an absorbed power-law model, with NH = 4.9 +/- 0.9 x 10^22 cm-2, and a photon index of 1.3 +/- 0.3. The source flux in the 0.3-10 keV band is 5.7 +/- 0.5 x 10^-10 erg/s/cm2 (uncorrected for absorption). Pile-up corrected spectra were extracted using the methods described by Evans et al (2009, MNRAS, 2009, 397, 1177).

A search of the Vizier catalogs reveals a star within the XRT error circle, with the identification as

USNO-A2.0 0600-29362287, RA=268.416289, dec=-25.753628, B=17.2 R=15.9
2MASS 17533994-2545129, RA=268.416419, dec=-25.753601, J=14.095 +/- 0.036 H=13.433 +/- 0.068 K=12.85

UVOT observed the field in the UVW1 filter. The UVOT image shows a faint source at the position of the USNO/2MASS star. We will report the magnitude and position of the UVOT source in a future ATel. An observation with the UVOT "B" filter has been requested.

Swift J1753.7-2544 continues to be detected in the Swift/BAT monitor. Its current rate (5 Feb. 2013) is 0.016 +/- 0.0017 ct/s/cm^2 (15-50 keV), which is the equivalent of 75 mCrab.

Swift/BAT Hard X-ray Transient light curve for Swift J1753.7-2544