TITLE: GCN GRB OBSERVATION REPORT NUMBER: 261 SUBJECT: GRB990123: Caltech STIS Photometry and Images DATE: 99/02/19 13:52:30 GMT FROM: Steve Odewahn at Caltech S. C. Odewahn, J. S. Bloom, S. Djorgovski, S. R. Kulkarni, and F. Harrison (CIT) report on behalf of the Caltech-NRAO-CARA GRB Collaboration: We have processed the HST STIS images of GRB 990123 using a variety of techniques and have deduced the following magnitudes: Estimates of Gunn r magnitudes from the Median stack STIS image: r(OT) = 25.25 -+0.2 systematic+accidental error r(OT+GAL) = 24.16 -+0.1 accidental error only r(A2) = 27.18 -+0.02 accidental error only r(OT+GAL+A2) = 24.09 Estimates of Gunn r magnitudes from the drizzled STIS image: r(OT) = 25.28 -+0.2 systematic+accidental error r(OT+GAL) = 24.12 -+0.1 systematic+accidental error r(A2) = 27.23 -+0.02 systematic+accidental error r(OT+GAL+A2) = 24.06 Details of the reduction, the image properties and a map defining the apertures for OT, GAL, and A2 (a discrete source 0.9" from the OT) may be found at: http://astro.caltech.edu/~sco/sco1/research/grb/grb990123/stis.html In this website we detail the procedure for obtaining by anonymous ftp our final STIS images, a deep Keck R-band image, and the Palomar 60-inch OT discovery image discussed in GCN 201. These data may be used without any need to cite the source. This message may be cited.