TITLE: GCN CIRCULAR NUMBER: 15646 SUBJECT: GRB 131231A: MDM afterglow observation DATE: 14/01/01 08:13:16 GMT FROM: Jules Halpern at Columbia U. J. P. Halpern (Columbia U.) reports: I observed the afterglow of GRB 131231A (Sonbas et al., GCN 15640; Xu et al., GCN 15641) using the 1.3m McGraw-Hill telescope of the MDM Observatory on 2014 January 1, from 01:40 to 03:18 UT. Nineteen 5-minute exposures were obtained in the R-band. Conditions were photometric, and the Landolt standard-star field around PG0231+051 was used for calibration. The afterglow magnitudes measured for the first and last exposures of the sequence are: -------------------------------- Jan 1 UT t-t0(hr) R +/- -------------------------------- 01:40 20.92 18.48 0.02 03:18 22.55 18.61 0.02 -------------------------------- The following stars in field were calibrated, and can be used for comparison: ----------------------------------------- Star R.A.(2000) Decl.(2000) R ----------------------------------------- A 00 42 30.4 -01 36 13 16.07 B 00 42 11.7 -01 37 29 17.95 C 00 42 15.9 -01 39 08 17.92 D 00 42 20.0 -01 41 53 17.22 E 00 42 28.8 -01 40 16 17.96 -----------------------------------------