Follow-up near-infrared observations of IGR J17497-2821

ATel #936; S. Chaty (AIM CEA Saclay/University Paris 7, France), H. Hatano (Dept. Astrophysics, Nagoya Univ., Japan), Y. Matsuoka (Inst. Astronomy, Univ. Tokyo, Japan), T. Nagata (Dept. Astronomy, Kyoto Univ., Japan)
on 7 Nov 2006; 22:11 UT
Credential Certification: Sylvain Chaty (S.Chaty@open.ac.uk)

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We report follow-up near-infrared (NIR) observations of IGR J17497-2821 (see Soldi et al. 2006, ATel #885), performed with the 1.4 m IRSF telescope at South African Astronomical Observatory (details on the observations and reduction are given in Chaty et al. 2006, ATel #897). We obtained J-, H- and Ks-band images of the field of IGR J17497-2821 for 21 nights during the period 2006 September 22nd to October 20th. More than 70% of the observations were photometric. These IRSF observations, with a pixel scale of 0.45", allow to study the Candidate 1, as labelled by Chaty et al. 2006 (ATel #906), but do not allow to distinguish both components constituting this blended object, as reported by Torres et al. 2006 (ATel #909).

We have analyzed the lightcurve of the blended object Candidate 1 during this observing period, and we obtained that its variations are similar to variations from other stars of the field of view, and constrained in an interval of 0.4 magnitudes, this interval being probably due to instrumental or sky variations. We can therefore conclude that the blended source did not exhibit any intrinsic variation in the NIR in an interval of 0.4 magnitudes during the period 2006 September 22nd to October 20th. We point out that, if the Ks=15.9 mag object reported by Torres et al. 2006 (Atel #909) is the real counterpart, its variations might be hidden by the presence of the brighter source Candidate 1.

We encourage follow-up NIR observations at higher spatial resolution, as soon as the source becomes visible again. These observations, with the source approaching the quiescence, should allow to detect any variation from both components of the blended object, and finally to pinpoint the real counterpart of IGR J17497-2821.