TITLE: GCN CIRCULAR NUMBER: 15654 SUBJECT: GRB 131224B detected in ground analysis of Swift-BAT data DATE: 14/01/02 23:45:09 GMT FROM: Jay R. Cummings at NASA/GSFC/Swift J. R. Cummings and D. M Palmer (Los Alamos) report on behalf of the Swift-BAT team: At 03:25:08 while Swift was executing a pre-planned slew, BAT detected a rate increase. In ground analysis, a significant source was found at RA, Dec 163.722, -14.177 which is RA (J2000) 10h 54m 53.3s Dec (J2000) -14d 10' 36" with an estimated 90% confidence error radius of 3 arcmin. This location was about 95% coded in the BAT field of view during the burst. The mask-weighted lightcurve shows two symmetrical peaks, the second peak about 1/3 the size of the first, each about 4 seconds long and separated by a gap of about 2 seconds. T90 is about 9 seconds. The average spectrum over 11 seconds is well fit by a simple power-law function with a photon index of 2.09 +- 0.20. The fluence was (2.6 +- 0.3) x 10^-7 ergs/cm^2. Errors are 90% confidence. Because this burst was noticed a week after it occurred, there is no followup planned with Swift.