Swift J1910.2-0546: Swift localization of a bright X-ray and optical counterpart
J. A. Kennea (PSU),  H. A. Krimm (CRESST/GSFC/USRA), 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 (CRESTT/GSFC/UMBC), G. Skinner (CRESST/GSFC/UMD), M. Stamatikos (OSU/GSFC), J. Tueller (GSFC), T. Ukwatta (MSU)
We report on Swift follow-up observations of Swift J1910.2-0546 (e.g. ATEL #4139, ATEL #4140) with the Swift X-ray Telescope (XRT). On June 1st at 14:41UT Swift began a target of opportunity observation of the BAT error circle of Swift J1910.2-0546, 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) = 287.59491 , -5.79943, which is equivalent to: RA(J2000) = 19h 10m 22.78s Dec(J2000) = -05d 47Ã¢â¬Â² 58.0Ã¢â¬Â²Ã¢â¬Â²,

with an estimated uncertainty of 3.5 arc-seconds radius (90% confidence). This position lies 1.6 arc-seconds from the optical/IR counterpart reported by Rau et al. (ATEL #4144), confirming that the counterpart is indeed Swift J1910.2-0546.

The pile-up corrected PC mode spectrum can be well fitted by an absorbed power-law model, with NH = 4.8 +/- 0.2 x 1021 cm-2, and a photon index of 3.3 +/- 0.1. The spectrum is not well fitted by an absorbed disk blackbody model, however a combination disk blackbody plus power-law model does improve the fit over a simple power-law. Using this model we derive the following parameters: NH = 2.9 +/- 0.4 x 1021 cm-2, kTin = 0.39 +/- 0.04 keV, Photon Index = 2.1 +/- 0.4. The source flux in the 0.3-10 keV band is 4.6 +/- 0.1 x 10-9 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).

UVOT observed the field in the b filter. We detect a new point source inside the XRT error circle, and co-incident with the IR counterpart with magnitude b=16.16 +/- 0.04 (AB system, not including a 0.02 magnitude systematic error). This source is not catalogued, nor is it seen when comparing UVOT images with DSS images of this field.

We note that the coordinates quoted by Rau et al. (ATEL #4144) contains an error in the sexagesimal value of the declination, the value should be 05:47:56.3 (note the transposed numbers in the seconds). Their quoted decimal value for declination is correct.
optical,x-ray,transient