TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  495
SUBJECT: GRB991216 Optical and IR observations
DATE:    99/12/19 00:15:32 GMT
FROM:    Peter Garnavich at Center for Astrophysics  <peterg@mars.harvard.edu>

P. Garnavich, S. Jha, K. Stanek, M. Pahre, M. Garcia, A. Szentgyorgyi
(CfA) and J. Tonry (U. Hawaii) report:

The object reported by Uglesich et al. (GCN 472) as a possible
afterglow of GRB991216 is detected on 5 sets of 120 sec. exposures
taken with the FLWO 1.2m+IRCam on Dec. 17 (UT) and on two sets of 540
sec. images taken Dec 18. A preliminary calibration provides the
following brightness estimates:

  UT Date     J     err
Dec. 17.35  16.99  0.05
Dec. 18.30  18.25  0.06

The power-law index derived from these data is -1.33. Our Dec. 18.
point is significantly fainter than the J-band observation reported by
Vreeswijk et al. (GCN 492) (UT 18.13).

The afterglow was again observed with the Hawaii 2.2-m in the R band
and calibrated using star "B" (Jha et al. GCN 476) with R=19.45 (Dolan
et al. GCN 486). These new brightness estimates are:

  UT Date     R    err
Dec 18.32  20.32  0.05
Dec 18.56  20.57  0.05

and when combined with previous R-band observations reported by Dolan
et. al (GCN 486), Henden et al. (GCN 473) and Jha et al. (GCN 476),
give a power-law index of -1.23+/-0.05. The Dec. UT 18.191 R-band
magnitude of 21.1 reported by Mattox (GCN 487) is significantly fainter
than our measurements.

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