The X‐Ray Position and Optical Counterpart of the Accretion‐powered Millisecond Pulsar XTE J1814−338

We report the precise optical and X-ray localization of the 3.2 msaccretion-powered X-ray pulsar XTE J1814-338 with data from the Chandra X-RayObservatory as well as optical observations conducted during the 2003 Junediscovery outburst. Optical imaging of the field during the outburst of thissoft X-ray transient reveals an R = 18 star at the X-ray position. This star isabsent (R > 20) from an archival 1989 image of the field and brightened duringthe 2003 outburst, and we therefore identify it as the optical counterpart ofXTE J1814-338. The best source position derived from optical astrometry is R.A.= 18h13m39.s04, Dec.= -33d46m22.3s (J2000). The featureless X-ray spectrum ofthe pulsar in outburst is best fit by an absorbed power-law (with photon index= 1.41 +- 0.06) plus blackbody (with kT = 0.95 +- 0.13 keV) model, where theblackbody component contributes approximately 10% of the source flux. Theoptical broad-band spectrum shows evidence for an excess of infrared emissionwith respect to an X-ray heated accretion disk model, suggesting a significantcontribution from the secondary or from a synchrotron-emitting region. Afollow-up observation performed when XTE J1814-338 was in quiescence reveals nocounterpart to a limiting magnitude of R = 23.3. This suggests that thesecondary is an M3 V or later-type star, and therefore very unlikely to beresponsible for the soft excess, making synchroton emission a more reasonablecandidate.Comment: Accepted for publication in ApJ. 6 pages; 3 figure