Optical observations of the candidate optical counterpart to XTE J1728-295 (=IGR J17285-2922)
ATel #2870; M. A. P. Torres (SRON/CfA), D. Steeghs (Warwick/CfA), P. G. Jonker (SRON/CfA/RU), N. R. Ross (UCLA)
on 24 Sep 2010; 21:23 UT
Credential Certification: Manuel Torres (firstname.lastname@example.org)
Subjects: Optical, Binary, Black Hole, Neutron Star, Transient
Following the recently announced subarcsec Chandra localization
for XTE J1728-295 (Chakrabarty et al. ATel #2869), we report on optical
observations of the field containing this currently active X-ray
transient (Atels #2823, #2824, #2825).
Our observations consist of several 60s and 180s i'-band images
acquired during 2010 Sep 8 23:55 - Sep 9 00:23 UT using the MagIC
camera mounted at the 6.5m Magellan Clay telescope. The data were obtained
with an image quality of ~0.4" and a 0.069"/pix plate
scale. Conditions were not photometric. An astrometric calibration of
the frames was defined using 2MASS stars in the field of
view. This delivered a positional accuracy < 0.1'.
From our images we measure a position of R.A.(J2000) =
17:28:38.86, Dec.(J2000) = -29:21:44.0 for the candidate optical
counterpart suggested in Russell et al. 2010, (ATel #2827). This
position is 0.5" away from the Chandra localization, but consistent
within the errors. Differential photometry of this optical source with
respect to nearby stars indicates no evidence for variability (< 0.01
mag) over the 28 min-long observation interval. Further visual
inspection of the data and PSF fitting reveal at least two other
point-like sources consistent with the 0.6' Chandra position and > 3
mag fainter than the proposed candidate.
Given the failure to detect variability(see also ATel #2827), we
encourage continued photometric observations and/or the acquisition of
a spectrum to confirm/find the candidate optical counterpart.