Columbia University Astronomy and 

MDM Observatory GRB Team

GRB 991216: MDM 1.3m R-band CCD Image
(J2000) 05 09 31.2, 11 17 7.2
1999 Dec. 17.142 -- 20 minute exposure
4.3 arcmin field rotated 50 deg CCW
1.3m CCD

GCN Circular #472: GRB 991216, Optical Afterglow
Robert Uglesich, Nestor Mirabal, J. Halpern (Columbia U.), Susan Kassin 
(Ohio State), & Sebastiano Novati (College de France) report on behalf 
of the MDM Observatory GRB follow-up team:

"We find a probable afterglow of the extremely bright BATSE burst GRB 991216
(Kippen et al. GCN #463) in a series of R-band observations taken by 
S. Kassin and S. Novati on the MDM 1.3m telescope.  An object at 
(J2000) 05:09:31.2, +11:17:07.2 faded from approximately R = 18.8 on
Dec. 17.142 to R = 19.4 on Dec 17.372.  The corresponding power-law decay 
index is -1.4. This object is not visible on the digitized POSS II plate.
Its position is consistent with the latest RXTE scan (Markwardt et al. 
GCN/RXTE_PCA notice). 

This preliminary photometry is based on several USNO stars.  We used a 
nonstandard broad R filter which transforms very well with Landolt R.

A finding chart is posted at

This message may be cited."

GRB 991216: MDM 1.3-m Difference Image Discovery Frame
(J2000) 05 09 31.2, 11 17 7.2
2.1 arcmin field

1.3m CCD
We used the image subtraction technique of Tomaney & Crotts(1996)
developed for the Columbia/VATT Microlensing Survey of M31
to efficiently search the entire field of view of our images for 
photometrically varying sources.  The optical transient was easily
detected as a source 16-sigma above background.  Left: 1200 second
R-band exposure taken on 1999 Dec 17.142 UT with the MDM 1.3-m 
telescope.  Right: Result of PSF-matching and subtracting a frame 
taken on 1999 Dec 17.372 from the image on the left.   
Robert Uglesich
Nestor Mirabal
Jules Halpern
Susan Kassin
Sebastiano Novati
Columbia University Astronomy and Astrophysics, Ohio State University,
College de France, and MDM Observatory

MDM Observatory