2005ApJ...627..910K

We report the precise optical and X-ray localization of the 3.2 ms accretion-powered X-ray pulsar XTE J1814-338 with data from the Chandra X-Ray Observatory as well as optical observations conducted during the 2003 June discovery outburst. Optical imaging of the field during the outburst of this soft X-ray transient reveals an R=18 star at the X-ray position. This star is absent (R>20) from an archival 1989 image of the field and brightened during the 2003 outburst, and we therefore identify it as the optical counterpart of XTE J1814-338. The best source position derived from optical astrometry is R.A.=18^h13^m39{fs}04, decl.=-33°46'22".3 (J2000). The featureless X-ray spectrum of the pulsar in outburst is best fit by an absorbed power law (with photon index γ=1.41±0.06) plus blackbody (with kT=0.95±0.13 keV) model, where the blackbody component contributes approximately 10% of the source flux. The optical broadband spectrum shows evidence for an excess of infrared emission with respect to an X-ray heated accretion disk model, suggesting a significant contribution from the secondary or from a synchrotron-emitting region. A follow-up observation performed when XTE J1814-338 was in quiescence reveals no counterpart to a limiting magnitude of R=23.3. This suggests that the secondary is an M3 V or later-type star and therefore very unlikely to be responsible for the soft excess, making synchrotron emission a more reasonable candidate.