TITLE: GCN GRB OBSERVATION REPORT NUMBER: 503 SUBJECT: Lowell/Perkins observation of GRB 991216 DATE: 99/12/20 13:34:44 GMT FROM: John Mattox at Boston U As suggested by Garnavich et al. (GCN 495), the Lowell/Perkins magnitude reported by Mattox in GCN 487 was indeed to faint by 0.8 magnitudes (due to the use of a preliminary flat with a large photometry radius). A series of 400s integrations were done in R band centered at 20.30 Dec. UT (under marginal conditions, 2.6" FWHM seeing, and with the nearly full moon 25 deg away). GRB 991216 is apparent in the sum of 14 images. A preliminary R magnitude is 22.3 +/- 0.2, which is fainter than the extrapolation of the power law of Jensen et al. (GCN 498). This discrepancy could result from an error in our preliminary reduction of these Lowell/Perkins data, or it could indicate a break in the decay slope due to evolution of a jet. This message should not be cited in publication - it is provided here to encourage observations which could confirm a break from the power law decay - a final reduction of these data will be linked to http://gamma.bu.edu/~mattox/grb.html when available.