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Further improved X-ray position and possible optical/nIR counterpart for XTE J1637-489

ATEL # 1704; R. Starling, P. Evans (University of Leicester) and R. Wijnands (University of Amsterdam)
on 8 Sep 2008; 15:07 UT
Password Certification: Rhaana Starling (

Subjects: Infra-Red, Optical, X-ray, Transients

We report a further refinement of the position of the recently discovered X-ray transient XTE J1637-498 (Markwardt, Pereira and Swank, ATEL #1699). Using 1 ks of Swift XRT Photon Counting mode data and 3 Swift UVOT v band images from the observation described in Wijnands et al. (ATEL #1700), we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue) of RA, Dec = 249.26112, -49.86128 deg which is equivalent to:
RA (J2000): 16 37 2.67
Dec (J2000): -49 51 40.6
with an uncertainty of 1.8 arcsec (radius, 90% confidence). This is 4.8 arcseconds from the centre of the previous X-ray position reported by Wijnands et al. (ATEL #1700). Position enhancement is described by Goad et al. (2007, A&A, 476, 1401), the current algorithm is an extension of this method.

This new position coincides with a single optical source clearly detected in each of the UVOT v band images of exposure times 76, 760 and 93 seconds respectively. We measure a preliminary v band magnitude of 18.4+/-0.3, which has a larger than typical error associated with it due to the presence of a nearby brighter star and a generally crowded field. This magnitude has not been corrected for the unknown but likely high expected Galactic extinction in this direction. We also note that the 2MASS source 16370267-4951401 lies at this position with the following magnitudes: J=14.556+/-0.156, H=13.848+/-0.269 and K=13.372+/-0.116.

The optical and nIR fields can be seen at

Further optical and IR observations are encouraged to determine the variability of the possible counterpart.

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