Near-infrared counterpart candidate to SLX 1746-331
ATel #1252; M. A.P. Torres (CfA), D. Steeghs (Warick/CfA), P. G. Jonker (SRON/CfA), J. Kennea (PSU), D. K. Erb (CfA), S. Gonzalez, C. R. Burns, W. L. Freedman (Carnegie)
on 30 Oct 2007; 04:26 UT
Credential Certification: Manuel Torres (firstname.lastname@example.org)
Subjects: Infra-Red, Binary, Black Hole, Transient
Referred to by ATel #: 1633
We report near-infrared observations with the 6.5m Magellan Baade
telescope at Las Campanas observatory of the field containing the
currently active black hole X-ray transient SLX 1746-331 (Markwardt &
Swank 2007, ATel #1235).
We have acquired a series of 15s Ks-band images on 2007 Oct 17 23:40 -
23:52 UT and again on 2007 Oct 22 23:45-23:57 using the PANIC camera
and totaling 450s on source for both nights. The frames were acquired
under good sky conditions with seeing of 0.5 arcsec. Additional 3s
exposures of the field were obtained for an absolute flux calibration
of the images. 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 of 0.1 mag.
Our imaging (see finding chart) revealed a large number of point
sources within the 4 arcsec error circle for the improved X-ray
location of SLX 1746-331 (Kennea et al. 2007; ATel #1237), Our
relative (PSF-fitting) photometry on the two data sets resulted in the
identification of only one variable object with Ks = 16.93 +/- 0.06 on
Oct 17 and Ks = 17.29 +/- 0.08 on Oct 22. We determined a position of
R.A(J2000)=17:49:48.94 and Dec(J2000)=-33:12:11.6 (+/- 0.1"
uncertainty) for this source. Note that the Oct 22 (MJD 54395.99) data
set was acquired when the X-ray flux had declined by a factor of ~2
compared to the X-ray flux measured on Oct 17 ((MJD 54390.99; see
public RXTE ASM light curve).
This variable source matches the Swift and ROSAT X-ray
positions and thereby we consider it a likely infrared counterpart to
SLX 1746-331. We plan to acquire additional imaging when the source
reaches quiescence to firmly establish the counterpart (if
visible at infrared wavelengths).