TITLE: GCN CIRCULAR NUMBER: 42414 SUBJECT: GRB 251023C: CALET Gamma-Ray Burst Monitor detection DATE: 25/10/24 04:00:02 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University kawakubo@phys.aoyama.ac.jp

Y. Asaoka (ICRR), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), 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 251023C (Swift/BAT-GUANO localization skymap: DeLaunay et al., GCN Circ 42412) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 16:24:24.93 UTC on 23 October 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1445271383/index.html). The burst signal was seen by all CGBM detectors.

The burst light curve shows a multi-peaked structure that starts at T+1.9 sec, peaks at T+3.7 sec, and ends at T+23.4 sec. The T90 and T50 durations measured by the SGM data are 18.7 +/- 1.4 sec and 5.7 +/- 0.8 sec (40-1000 keV), respectively.

The ground-processed light curve is available at

https://cgbm.calet.jp/cgbm_trigger/ground/1445271383/

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

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