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On the NIR counterpart to IGR J17497-2821

ATEL # 909; M. A. P. Torres, D. Steeghs (CfA), P. G. Jonker (SRON/CfA), C. R. Burns, W. L. Freedman (Carnegie)
on 4 Oct 2006; 8:53 UT
Password Certification: Manuel Torres (

Subjects: Infra-Red, Binaries, Black Holes, Neutron Stars, Transients

We report near-infrared (NIR) observations of the field containing the X-ray transient IGR J17497-2821 (Soldi et al., ATel #885). On 2006 Sep 21 23:34-23:40 UT we acquired Ks-band images with the 6.5m Magellan Baade telescope using the PANIC camera and totaling 225s on source respectively. The images were acquired under variable sky conditions with ~0.75" seeing, and we excluded frames with high background events before combining them. This left us with a net total time of 135s on source. An astrometric scale was defined using ten 2MASS sources in the field of view.

Several sources have previously been reported to be within the Swift error circle (Laycock et al, ATel #895; Chaty et al. ATel #897, #906) and our images also show a large number of sources consistent with the 5" Swift position. The recent announcement of a 1" precision Chandra localization (Paizis et al., ATel #907) has significantly improved the chances of identifying the correct counterpart. Note that a K=13.1 mag candidate has been suggested on the basis of its coincidence with the Chandra localization for the X-ray source (ATel #906, #907). This candidate is 0.57" away from the Chandra X-ray position.

Our images show that this reported NIR candidate (ATel #907) is actually a blend of two sources, with an additional fainter component to the North-West (see linked image). We determined a position of RA=17:49:38.039 and Dec=-28:21:17.5 (+/- 0.1" uncertainty) for this component. Preliminary relative (PSF-fitting) photometry with respect to 2MASS stars yields Ks=15.9 +/- 0.2 for this source.

We remark that this additional source that has not previously been reported matches the Chandra position very well (it is 0.1" +/- 0.1" away), and thus must be considered a likely counterpart candidate to IGR J17497-2821. We plan to acquire additional imaging as the source evolves to firmly establish the correct counterpart (if visible at NIR wavelengths).

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