TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  2499
SUBJECT: GRB031220: Palomar Observations
DATE:    03/12/21 12:30:45 GMT
FROM:    Derek Fox at CIT  <derekfox@astro.caltech.edu>

D.B. Fox, A.M. Soderberg and E.Berger (Caltech) report on behalf of
a larger collaboration:  

"We have observed the HETE-2/SXC localization region for GRB 031220
through intermittent clouds with the Palomar 200-inch (5-m) Hale
Telescope and Large Format Camera (LFC) from 08:30 to 10:00 UT on 20
Dec 2003.  With a subset of these data we have created two coadded r'
images with exposures of approximately 24-min over the full SXC region
and with mean epochs of 08:50 UT (5:20 after the GRB) and 09:47 UT
(6:17 after the GRB), respectively.  The limiting magnitudes of these
images, as referenced against the R-band (F-emulsion) photometry of
the GSC-2, are R~23 and R~22.5, respectively, with the later
observations having been more strongly extinguished by cloud cover.

Comparison of these images to the Digitized Sky Survey reveals no new
objects brighter than the DSS limit.  Moreover, PSF-matched image
subtraction of the two images reveals no strongly variable sources
significantly brighter than our limits.  Since a t^(-1) decay would
have produced a 0.2 mag decline between the two epochs of exposure, we
estimate that any afterglow of GRB 031220 had R>21 at our epoch of
first observation.

Our coadded r' images, and their subtraction, may be found at:

    http://www.astro.caltech.edu/~derekfox/grb031220/