[vsnet-grb-info 6822] GRB081024B: P200 Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8417
SUBJECT: GRB081024B: P200 Observations
DATE:    08/10/27 05:23:08 GMT
FROM:    S. Bradley Cenko at Caltech  <cenko at srl.caltech.edu>

S. B. Cenko (UC Berkeley) and M. M. Kasliwal (Caltech) report on behalf of
a larger collaboration:

We have imaged the error circle of the short duration GRB081024B (Omodei,
GCN 8407; Connaughton and Briggs, GCN 8408) with the Large Format Camera
mounted on the Palomar 200 inch Hale telescope.  Images were taken in
the Sloan r' and i' filters at a mean epoch of approximately Oct 26.1 (~
30 hours after the burst).

We detect several sources inside or near the potential X-ray afterglow
(XRT Source 2; Guidorzi, Margutti, and Mao, GCN 8410; Guidorzi and
Margutti, GCN 8416).  Calibrating with respect to several nearby objects
in the USNO-B1 catalog, we note the following positions and magnitudes for
the four nearest sources:

O1 -  RA: 21:31:36.95   Dec: +21:16:35.4 (J2000.0)
      R = 20.6 mag

O2 -  RA: 21:31:37.63   Dec: +21:16:33.0 (J2000.0)
      R = 22.6 mag

O3 -  RA: 21:31:37.42   Dec: +21:16:36.4 (J2000.0)
      R = 23.4 mag

O4 -  RA: 21:31:37.32   Dec: +21:16:25.1 (J2000.0)
      R = 22.6 mag

We estimate the astrometric precision for each source is 0.5" in each
coordinate.  The photometric precision for the above reported magnitudes
is likely large (~ 0.3 mag) due to both zeropoint uncertainty and
bandpass differences.  The limiting magnitude of our co-added image is
approximately R > 23.5 mag.

We note that source O1 appears to be present in the DSS plates of this
field.  Additionally, source 02 is clearly extended.  None of the objects
show evidence for variability over the (limited) duration of our
observations.

An image of the field is posted at:

   http://www.srl.caltech.edu/~cenko/public/grb081024b.jpg

Further observations to search for variability are encouraged.