TITLE: GCN CIRCULAR NUMBER: 31333 SUBJECT: GRB 211227A: CALET Gamma-Ray Burst Monitor detection DATE: 21/12/29 08:03:36 GMT FROM: Valentin Pal'shin at AGU val@phys.aoyama.ac.jp

M. L. Cherry (LSU), A. Yoshida, T. Sakamoto, V. Pal'shin, S. Sugita (AGU), Y. Kawakubo (LSU), K. Yamaoka (Nagoya U), S. Nakahira (RIKEN), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration:

The long GRB 211227A (Swift detection and refined analysis: Beardmore et al., GCN Circ. 31316, Lien et al., GCN Circ. 31326; MAXI/GSC detection: Tominaga et al., GCN Circ. 31319; https://gcn.gsfc.nasa.gov/other/211227A.gcn3) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 23:32:07.476 UTC on 27 December 2021. The burst signal was seen by all CGBM detectors. Because of a problem in one of the ground alert processing script, the GCN notice was not distributed automatically for this event.

The burst light curve shows a multi-peaked structure which starts at T-0.6 sec and ends at T+77.2 sec. The T90 and T50 durations measured by the SGM data are 64.5 +- 10.3 sec and 22.0 +- 2.0 sec (40-1000 keV), respectively.

The ground processed light curve is available at

http://cgbm.calet.jp/cgbm_trigger/ground/1324683113/

The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at the Waseda University.