TITLE: GCN CIRCULAR NUMBER: 42402 SUBJECT: GRB 251023B: CALET Gamma-Ray Burst Monitor detection DATE: 25/10/23 16:16:02 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University kawakubo@phys.aoyama.ac.jp

S. Nakahira (JAXA), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), Y. Asaoka (ICRR), S. Torii, Y. Akaike, K. Kobayashi (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration:

The long GRB 251023B (MAXI/GSC Detection: Kang et al., GCN Circ 42392) was detected in the ground analysis of the CALET Gamma-ray Burst Monitor (CGBM) data around 08:49:03 on 23 October 2025 (referenced to the MAXI detection: GCN Circ. 42392). (https://cgbm.calet.jp/cgbm_trigger/flight/1445244062/index.html). The burst signal was seen by all CGBM detectors.

The burst light curve shows a multi-peaked structure that starts at T-31.7 sec and ends at T+8.2 sec. The T90 and T50 durations measured by the HXM2 data are 34.9 +/- 4.2 sec and 16.7 +/- 2.2 sec (7-100 keV), respectively.

The ground-processed light curve is available at

https://cgbm.calet.jp/cgbm_trigger/ground/1445244062/

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

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