GCN Circular 201

GRB 990123: Bright New Source, Possible Optical Transient

S. C. Odewahn, J. S. Bloom, and S. R. Kulkarni (CIT) report on behalf of
the Caltech-NRAO-CARA GRB Collaboration:

"We imaged the BeppoSAX localization (Piro et al. 1999; GCN #199) of GRB
990123 with a CCD camera on the Palomar 60-inch. In each 400-s R-band
image a source clearly brighter than on DSS was seen at position: RA,DEC =
15:25:30.53, +44:46:00.5 (J2000) (preliminary astrometry).  This
localization is well-within the BeppoSAX error radius.  Though DSS and
R-band are somewhat different bandpasses, given the apparent brightness
of the source relative to the DSS image, we suggest that this source is
the optical transient of GRB 990123.

A faint source at the limit of detectability is seen on the POSS-II
image at this location and we suggest this may is the host galaxy of
the GRB.  If true, we have discovered the brightest host galaxy of any
GRB known thus far --- this would be commensurate with the expectation,
based on the high GRB flux as measured by BeppoSAX, that this burst is
nearer than any localized previously.

Preliminary photometry based on the APM catalogue puts the optical
transient at R = 18.2 (Jan 23.565 UT) and the host galaxy at R ~= 21.3.
More precise photometric and astrometric calibrations are currently under
way.

The discovery image may be obtained at the following web page:
    http://astro.caltech.edu/~jsb/GRB/grb990123.html

Follow-up of this most bright burst is urged at all wavelengths.


This message may be cited."