TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  510
SUBJECT: GRB 991216: Detection of the Host and/or Absorber Galaxy
DATE:    99/12/30 07:20:37 GMT
FROM:    George Djorgovski at Caltech/Palomar  <george@oracle.caltech.edu>

GRB 991216: Detection of the Host and/or Absorber Galaxy

S. G. Djorgovski (CIT), R. Goodrich (CARA), S. R. Kulkarni, J. S. Bloom,
A. Dierks, F. Harrison (CIT), and D. A. Frail (NRAO) report on behalf of
the Caltech-CARA-NRAO GRB collaboration:

We obtained R-band images of the field of GRB 991216 using the ESI instrument
on the WMKO Keck-II telescope, on UT 1999 Dec 29.41.  The OT is well detected
with an estimated magnitude R = 23.6, marginally fainter than the extrapolation
of the early power-law light curve, possibly indicative of a change in the
decline rate.  We detect a galaxy extending out to ~ 1 arcsec to the W of the
OT, with an estimated magnitude R ~ 24.5, not including any portion of the
galaxy covered by the OT image.  We propose that this is the host galaxy of
the GRB, which may be also responsible for the z = 1.02 absorption system
reported by Vreeswijk et al. (GCN #496).  Its low-resolution spectra show no 
obvious strong line emission in a very rough, preliminary reduction.  Another 
galaxy of a comparable magnitude (R ~ 24.8 mag) is detected 2.4 arcsec to the 
SE of the OT; it may be responsible for another absorption system reported in 
the spectrum of the OT.  These magnitudes have the zero-point uncertainty of 
at least 0.3 mag, due mainly to the aperture corrections.

Images of the field will be posted at
http://astro.caltech.edu/~george/grb/grb991216.html

This note can be cited.