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ATEL # 2190; M.A.P. Torres (CfA), D. Steeghs (Warick/CfA), P. G. Jonker (SRON/CfA), J. E. McClintock (CfA), N. Morrell, M. Roth (LCO)
on 4 Sep 2009; 21:29 UT
Password Certification: Manuel Torres (firstname.lastname@example.org)
Subjects: Infra-Red, Black Holes, Neutron Stars, Transients
We report on near-infrared follow-up observations of the field containing the currently active X-ray transient XTE J1652-453 (Markwardt et al. ATel #2107, #2120). A Ks= 16.9 +/- 0.3 mag NIR counterpart candidate has been suggested on the basis of its coincidence with the radio localization for the X-ray source (Calvelo et al. ATel #2135, Reynolds et al. ATel #2125).
We have acquired a series of 15s Ks-band images on 2009 Jul 15 23:02 - 23:14 UT and again on 2009 Aug 28 23:33-23:46 using the PANIC camera attached to the 6.5m Magellan Baade telescope at Las Campanas observatory. The frames (totaling 450s on source for both nights) were acquired under good sky conditions with seeing of 0.8'' and 0.4'', respectively. Additional 3s exposures of the field were obtained during the first night for an absolute flux calibration of the data. The astrometric and photometric scale were defined using 2MASS sources in the field of view achieving a positional RMS of 0.1 arcsec and a zero-point error < 0.1 mag.
Our relative (PSF-fitting) photometry on the two data sets shows no significant variability for the suggested NIR counterpart (labeled as star B in Reynolds et al. ATel #2125). We determine a mean magnitude of Ks = 16.9 +/- 0.1. Note here that the Aug 28 (MJD 55071.98) data set was acquired when the X-ray flux had declined by a factor of ~4 compared to the X-ray flux measured on Jul 15 (MJD 55027.96; see RXTE PCA light curve).
The non-variable nature of star B suggests that it could be an unrelated interloper star and that the NIR counterpart was fainter than Ks=19 (Jul) and Ks > 20 (Aug) as estimated from the 3-sigma upper limit magnitudes of our images. For completeness sake, we also determine Ks-band magnitudes of 16.508 +/- 0.05, 14.421 +/- 0.005, 15.219 +/- 0.011 and 15.808 +/- 0.016 for stars A, 1,2 and 3 as labeled in Reynolds et al.