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ATEL # 1508; M. A. P. Torres (CfA), D. Steeghs (Warwick/CfA), G. Roelofs (CfA), P. G. Jonker (SRON/CfA)
on 4 May 2008; 5:37 UT
Password Certification: Manuel Torres (email@example.com)
Subjects: Binaries, Neutron Stars, Transients
Following the recent announcement of a 0.6 arcsec precision Chandra localization for the neutron star X-ray transient XTE J1810-189 (Chakrabarty, Jonker \& Markwardt 2008, ATel #1490), we have reviewed the infrared observations presented in Torres et al. (2008 ATEl #1446) to identify possible counterparts.
The data consist on Ks-band images obtained on 2008 Mar 18 09:51-9:57 UT and totaling 225s on source (see ATel #1446 for more details). Sky conditions were good with a seeing of ~0.5 arcsec. Additional 3s exposures of the field were obtained the same night to derive the astrometric and absolute flux calibration of the frames relative to 2MASS. The astrometric and photometric scales were defined using 2MASS objects in the field achieving a positional RMS < 0.2 arcsec and a photometric zero-point error < 0.1 mag.
Our images show a number of blended sources consistent with the Chandra position. These sources are actually a bright point-like source, with at least two fainter components to the South-West (see linked finding chart). We determined a position of RA(J2000)=18:10:20.86 and Dec(J2000)=-19:04:11.1 for the brightest component. Preliminary relative (PSF-fitting) photometry yields Ks=17.3 +/- 0.2 for this source.
These sources match the Chandra position very well and thus must be considered likely counterpart candidates to XTE J1810-189. We plan to obtain additional imaging as the source decays in X-rays to firmly establish the correct counterpart if visible at infrared wavelengths.