Near-IR observations of the X-ray transient Swift J174540.2-290005 in the Galactic Center
ATel #935; Z. Wang (McGill), F. K. Baganoff (MIT), M. Muno (Caltech), M. Morris (UCLA), N. Morrell (LCO), A. Muzzin, D. Gilbank, P. Hsieh (Toronto), D. Kaplan (MIT)
on 7 Nov 2006; 13:46 UT
Credential Certification: Z. Wang (wangzx@physics.mcgill.ca)
Subjects: Infra-Red, Binary, Black Hole, Neutron Star
We observed the field of the Galactic center (GC) transient
Swift J174540.2-290005 on 2006 October 30 and 31 at Ks band,
using the near-IR imaging camera PANIC (Persson's Auxilliary Nasmyth
Infrared Camera) on the Magellan/Baade Telescope at Las Campanas
Observatory in Chile. The exposures were 3.3 and 6.7 min in the first
and second night, reaching the limiting magnitudes of 17.3 and 17.7 mag
(3-sigma), respectively. We did not detect any sources within
the improved 0.4 arcsec Chandra error circle (90% confidence;
Muno et al. 2005 ApJ 622 L113), while we note that there were two faint
sources within a typical 0.7 arcsec Chandra error circle (90% confidence)
and a dozen of sources within the 3.6 arcsec Swift error circle
(90% containment; ATel #921).
Comparing the two images to a Ks image of the same field that
we obtained on 2005 May 25 with an exposure of 0.83 min
and using the same telescope/instrument, we did not detect any
significant brightening from any of the sources. This supports that
none of them was the counterpart to CXOGC J174540.0-290005
(Muno et al. 2005), since we expect a correlated IR flux brightening,
either by approximately 0.5 mag for a high-mass X-ray
binary (e.g., Clark et al. 2000 A&A 356 50) or several magnitudes
for a low-mass X-ray binary (LMXB; e.g., Russell et al. 2006 MNRAS 371
1334).
Our IR observations would detect a main sequence star down to
spectral type B5 (assuming a source distance of 8.0 kpc and a
reddening Av=31 to the GC), suggesting that, if this transient
is an X-ray binary with an accreting neutron star or black hole
(Muno et al. 2005), it would likely be a LMXB.
