TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1696 SUBJECT: GRB 021112: Variable Source in R-band search DATE: 02/11/18 22:49:28 GMT FROM: James Rhoads at STScI L. Strolger, J. E. Rhoads, A. Fruchter, I. Burud (STScI); A. J. Levan (Leicester), and J. J. Kavelaars (McMaster) report. In follow-up to our observations reported in GCN 1684, additional observations of the GRB 021112 error box (GCN 1682) were made using the KPNO-4m + Mosaic I imager on UT 2002 November 13.2. Four R-band images were obtained dithered to cover the entire HETE-2 error circle, for a combined exposure time of 1680s. Further detailed analysis of the field, including localized registration, PSF-matching, and subtraction of the combined observations made Nov. 12.3 from the combined observations made Nov. 13.2 have revealed a candidate optical transient (OT) located just outside the HETE-2 90% error circle, at RA: 02:38:27.80 Dec: +48:33:18.4 (J2000.0) Coordinates and offsets from neighboring stars were determined from direct comparison to the DDS-2 (R-band). A source is visible at the limit of the DDS-2 red plate at the position of the variable object. PSF photometry performed on the candidate OT and 5 neighboring stars have shown the object apparently brightened by 0.55 +/- 0.03 magnitudes between the observations made on Nov. 12.3 and Nov 13.2. Further information summarizing the discovery and analysis can be found on http://www.stsci.edu/~fruchter/GRB/021112/ . An approximate photometric zero point (based only on the typical throughput for the camera) gives R=21.1 on Nov 12.3 and R=20.6 on Nov. 13.2. Local reference star magnitudes are given on the above web page to facilitate comparison with other data.