TITLE: GCN GRB OBSERVATION REPORT NUMBER: 201 SUBJECT: GRB 990123: Bright New Source, Possible Optical Transient DATE: 99/01/23 17:18:18 GMT FROM: Josh Bloom at CIT 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."