Eclipsing X-ray Burster in Terzan 5: Improved Swift Localization

ATel #2937; J. A. Kennea (PSU), P. A. Evans and A. P. Beardmore (U Leicester)
on 14 Oct 2010; 17:35 UT
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Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)

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We have examined the Swift/XRT on-axis photon counting mode observation of the recently detected transient LMXB/Pulsar in Terzan 5 (e.g. Bordas 2010, ATEL #2919). Utilizing PSF fitting technique which compensates for the presence of a masked out hot column that dissects the PSF, and UVOT data to correct for systematic errors in the astrometry using the method described by Evans et al. (2009, MNRAS, 397, 1177), we find an improved position of the transient of RA, Dec(J2000) = 267.01987, -24.78050, which is the equivalent of:

RA (J2000): 17h 48m 4.77s
Dec (J2000): -24d 46m 49.8s

with an estimated error radius of 2.3 arcsec (90% confidence), this position lies 3 arcsec from the XRT derived position reported by Heinke et al. (2010, ATEL #2933). Inside this error circle are the Heinke et al. (2006, ApJ, 651, 1098) reported sources CX33, CX25 (noted to be a possible quiescent LMXB candidate) and CX28, 1.1 arcsec, 1.3 arcsec and 1.8 arcsec from the center of the XRT error circle respectively. Outside of the 90% confidence region the next two closest objects are CX37 (3.3 arcsec distance) and CX 35 (4.5 arcsec distance). We note that this position lies 6.8 arcsec from the candidate counterpart of EXO 1745-248 (AKA CX 3), most likely ruling out that this current transient as a recurrence of the 2000 transient outburst source, in agreement with the conclusion of Heinke et al. (2010, ATEL #2933).