GCN Circular 517
Bradley E. Schaefer (Yale) reports: "I have obtained deep R-band images with the 3.5m WIYN telescope on Kitt Peak starting on January 6, 2000 at 04:35 UT. The images had 0.6-0.8" FWHM seeing and used the Harris-R filter on the Mini-Mosaic camera. After standard processing, IRAF APPHOT photometry (with 0.6" radius aperture) was used. The only calibrated star which was unsaturated in my images is Star B, with R=19.45+-0.03 (Dolan et al. GCN 486). The optical transient is still visible with a SNR~7 within 0.3" of the radio position. My two measures of the optical transient magnitude are R=24.20+-0.15 and R=24.24+-0.20. These observations were taken around the time when a possible underlying supernova would be at peak. However, if the red shift is 1.02 or greater (Vreeswijk et al. GCN 496) and the supernova is like SN1998bw, then the supernova light should be fainter than R~25.0 (Bloom et al. 1999, Nature, 401, 453). An extrapolation of the afterglow light curve from the first few days of the burst gives either 23.45+-0.14 (Garnavich et al. GCN 495; index=-1.23+-0.05) or 23.66+-0.25 (Jensen et al. GCN 498; index=-1.17+-0.10). Thus, my combined magnitude (R=24.21+-0.12) is two-sigma fainter than the faintest of these extrapolations. (A similar result was found by Djorgovski et al. [GCN 510] for an observation on December 29, 1999.) An index of -1.40+- 0.06 since several days after the burst is needed to satisfy my observed magnitudes. It is possible that this is a break in the afterglow light curve (like for GRB990510) due perhaps to the evolution of a jet."