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
Not found
 
 
).  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
Not found
 
 
) 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
Not found
 
 
;
index=-1.23+-0.05) or 23.66+-0.25 (Jensen et al. GCN 498
Not found
 
 
;
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."