TITLE: GCN CIRCULAR NUMBER: 18706 SUBJECT: GRB 151212B: CALET Gamma-Ray Burst Monitor detection DATE: 15/12/17 07:53:13 GMT FROM: Takanori Sakamoto at AGU I. Takahashi, A. Yoshida, T. Sakamoto, Y. Kawakubo, 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: The long-duration GRB 151212B (Fermi-GBM trigger #471576728) triggered the CALET Gamma-Ray Burst Monitor (CGBM) at 01:32:04.68 UT on 12 December 2015. The clear burst signal was detected by the Soft Gamma-ray Monitor (SGM; 30 keV - 20 MeV) which is a scintillation detector utilized a BGO crystal. Due to a large incident angle of the event, no signal was detected by the Hard X-ray Monitor (HXM; 7 keV - 1 MeV) which is a scintillation detector composed of a LaBr3(Ce) crystal. The light curve of the SGM shows the main peak starting from T0, peaking at T0+1 sec and ending at T0+4 sec. The T90 duration measured by the SGM data is 3.5 +- 0.5 sec (40-460 keV). Currently, CALET is in the commissioning phase. Further information about CALET and CGBM can be found at http://calet.jp/en/ and http://www.en.yoshida-agu.net/research/calet-gbm