On the NIR counterpart candidate to XTE J1652-453
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
Credential Certification: Manuel Torres (mtorres@cfa.harvard.edu)
Subjects: Infra-Red, Black Hole, Neutron Star, Transient
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.
