TITLE: GCN CIRCULAR NUMBER: 18792 SUBJECT: GRB 151227B: CALET Gamma-Ray Burst Monitor detection DATE: 15/12/31 22:37:10 GMT FROM: Takanori Sakamoto at AGU K. Senuma, A. Yoshida, T. Sakamoto, I. Takahashi, Y. Kawakubo, 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: The long-duration GRB 151227B (Toelge et al. GCN Circ. 18727; Hurley et al. GCN Circ. 18773; Golenetskii et al. GCN Circ. 18781) triggered the CALET Gamma-Ray Burst Monitor (CGBM) at 5:13:49.89 UT on 27 December 2015. The clear burst signal was detected by HXM1 and SGM instruments. The light curve of the SGM shows three main peaks. The first peak starts at T0, peaks at T0+2 sec and ends at T0+4 sec. The brightest second peak, which consists of various sub-peaks, starts at T0+20 sec, peaks at T0+31 sec and ends at T0+40 sec. The third peak starts at T0+40 sec, peaks at T0+45 sec and ends at T0+50 sec. The T90 duration measured by the SGM data is 42.0 +- 0.3 sec (40-1000 keV). The CGBM data used in this analysis are provided by the Waseda CALET Operation Center located at the Waseda University.