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The NIR counterpart to XTE J1747-274(=IGR J17473-2721)

ATel #634; M. A.P. Torres, D. Steeghs, M. R.Garcia, J. E.McClintock (CfA), P. G.Jonker (SRON/CfA), P. J.Callanan (UCC)
on 18 Oct 2005; 19:47 UT
Credential Certification: Danny Steeghs (dsteeghs@cfa.harvard.edu)

Subjects: Infra-Red, X-ray, Binary, Black Hole, Neutron Star, Transient

We report follow-up observations confirming the near-infrared (NIR) counterpart to the X-ray transient XTE J1747-274/IGR J17473-2721 (ATEL #467, #498). A Ks=16.2 mag candidate was suggested in ATEL #521 on the basis of its coincidence with the Chandra localization for the X-ray source. The candidate appeared extended and/or blended with a nearby NIR source to the south.

Our observations consist of a series of Ks-band images obtained with the 6.5m Magellan Baade telescope between 2005 Sep 13 02:06-02:26 UT using the PANIC camera and totaling 375s on source. The frames were acquired with a seeing of 0.8 arcsec and a projected pixel size of 0.125 arcsec on the 1024x1024 Hawaii detector. Photometric and astrometric scales were defined using 2MASS sources in the field of view.

Our images show a single point-like source 0.3-0.4 arcsec south from the position reported for the NIR candidate (ATEL #521). This source is likely associated with a field star and the cause of the reported extension of the counterpart during outburst. The proposed counterpart candidate has thus faded significantly and is not detected with a 3-sigma upper limit magnitude of Ks>17.4.

This large decrease in brightness relative to the observations reported when the transient was active confirms the candidate reported in ATEL #521 is indeed the NIR counterpart to XTE J1747-274/IGR J17473-2721.