GCN Circular 213

GRB 990123:  Pre-Burst Detection of an Apparent Host Galaxy

R. R. Gal, S. G. Djorgovski, S. C. Odewahn, J. S. Bloom, and S. R. Kulkarni
(CIT), on behalf of the Caltech DPOSS team and the Caltech-CARA-NRAO GRB
collaboration report:

A faint galaxy coincident with the optical transient discovered at Palomar
(Odewahn et al., GCN Circ. 201
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  and IAUC 7094) was detected on the F (red)
plate of Digital POSS-II (DPOSS), taken on 05 July 1994 UT.  The galaxy was
not detected on J (blue/green) and N (near-IR) plates taken in March 1993.

Using the new CCD calibration of the field, we obtain for the galaxy the
Gunn magnitude r = 21.9 +- 0.4 (corresponding to Johnson R = 21.5 +- 0.5).
Our preliminary calibration gives the upper limits in the other two band,
with g > 22.4 (roughly, B > 22.0), and i > 20.6 (roughly, I > 19.9), with
a net uncertainty of about 0.5 mag.  The limits in g and i are consistent 
with the plate limits and the weak detection in the r band, for typical
galaxies at these magnitude levels.

At this r band magnitude level, the typical redshift for a normal field 
galaxy is about 0.2 to 0.3.  It is extremely unlikely that this galaxy is 
at z > 0.5, unless it contains an active nucleus.  Future spectroscopic 
observations will establish if this is indeed the host galaxy of GRB 990123.

The DPOSS image can be seen at:
http://astro.caltech.edu/~george/grb/grb990123.html

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