TITLE: GCN CIRCULAR NUMBER: 18724 SUBJECT: GRB 151225A: CALET Gamma-Ray Burst Monitor detection of a possible short GRB DATE: 15/12/26 02:37:37 GMT FROM: Takanori Sakamoto at AGU Y. Kawakubo, A. Yoshida, T. Sakamoto, I. Takahashi, K. Senuma, M. Moriyama, Y. Yamada (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), Y. Asaoka, S. Ozawa, S. Torii (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena) and the CALET collaboration: A possible short-duration GRB 151225A (trigger #1135105601) triggered the CALET Gamma-Ray Burst Monitor (CGBM) at 19:09:10.34 UT on 25 December 2015. The clear burst signal was detected by all three CGBM instruments. The light curve of the SGM shows a double peak structure. The initial spike starts and peaks around T0. The second peak starts around T0+0.5 sec, peaks around T0+0.7 sec and ending around T0+1.5 sec. Above 500 keV band, the first peak looks insignificant, instead the 2nd peak is clearly visible. Based on the light curve inspection, the signal is clearly visible up to ~1.5 MeV. Low energy data show no significant soft extended emission above ~7 keV. The T90 duration measured by the SGM data is 1.87 +- 0.13 sec (40-450 keV). Identification of this possible short event by other spacecraft is strongly encouraged.