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GCN Circular 517

GRB991216 late optical observation
2000-01-08T01:26:51Z (24 years ago)
Brad Schaefer at Yale U <>
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

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."
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