TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  176
SUBJECT: GRB 981220:Optical Observations
DATE:    98/12/29 04:26:33 GMT
FROM:    Shri Kulkarni at Caltech  <srk@astro.caltech.edu>

GRB 981220: Optical Observations

A. C. Eichelberger, J. S. Bloom, S. R. Kulkarni, R. R. Gal (Caltech),
E. G. Martin (UCB), and D. A. Frail (NRAO) report:

On December 23, 1998 (UT) we obtained four 300-s R-band imaging of the
field of GRB 981220 with LRIS on the Keck II 10-m telescope. Based on
astrometry from the USNO-A2 catalogue, at the position of the transient
radio source (RT; GCN #170) we find a faint source in the stacked
image. Our astrometry is good to 0.3 arcsec (rms) in each coordinate.
Lacking observations of standard stars, we have used the standard
R-band zeropoint of LRIS.  Using a 1.2 arcsec aperture we find the
object at the position of the RT to have R= 26.7 +/- 0.7 mag on 23.4
Dec 1998 UT. For reference, this zeropoint implies that the USNO star
at ra: 03:42:28.32, dec:  +17:09:42.60 (J2000) has a magnitude of
R=18.35.

Although the object appears somewhat extended in our 0.8 arcsec (FWHM)
seeing, deeper imaging is required to firmly establish that this object
is indeed the host galaxy of the GRB.

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