The HST observation consists of dithered pair of images (4400 seconds) in the
wide-V (F606W) filter, and a 2400 second wide-U (F300W) image.
The central 400 X 400 pixels (17.7 X 17.5 arcsec) of the planetary camera
images are plotted. The arrow at the lower right of the F606W image points
north.Both images are heavily stretched to bring out the faint features.
The data were reduced using the WFPC2 team reduction method, which
includes application of a high signal-to-noise superdark frame
composed of dark frames taken as near as possible in time to the date
of the observations, as well as an updated warm pixel correction for
highly time-dependent dark current by using a delta (local) dark frame.
All images were CR-SPLIT to facilitate cosmic-ray removal. The CR-SPLIT
exposures were co-added using the VISTA "PICCRS" package. Final cosmic ray
identification was done by blinking the split exposures in each filter.
Residual cosmic rays were hand-cleaned only in the vicinity of the neutron
star; they are evident elsewhere in the images.
The dithered F606W frames were co-added using a simple adaptation of the
Fruchter & Hook "drizzling" algorithm; we
employed a 2X2 oversampling and a drop size of 1X1 oversampled
We identified the marked object as the optical counterpart.
Its properties are:
- f606W magnitude = 25.9 (ST system), 25.6 (Vega system)
- f300W magnitude = 23.4 (ST system)
- f606W-f300W color = -2.5 (hot black body has color = -3 in the ST system).
- estimated U-V: -1.2
- position: 18 h 56 m 35.41 s -37 54' 35.8" (J2000), on the Digital
Sky Survey reference frame. This is 2.0 arcsec from the revised X-ray
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