TITLE: GCN CIRCULAR NUMBER: 42027 SUBJECT: GRB 250926A: CALET Gamma-Ray Burst Monitor detection DATE: 25/09/29 15:19:54 GMT FROM: Yuta Kawakubo at Aoyama Gakuin University kawakubo@phys.aoyama.ac.jp

S. Ricciarini (U of Florence), A. Yoshida, T. Sakamoto, S. Sugita, Y. Kawakubo (AGU), K. Yamaoka (Nagoya U), S. Nakahira (JAXA), 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), P. S. Marrocchesi (U of Siena), and the CALET collaboration:

The GRB 250926A (Fermi GBM Final Real-time Localization: Fermi GBM team, GCN Circ. 41993; AstroSat CZTI detection: Goyal et al., GCN Circ. 42008; Insight-HXMT detection: Wang et al., GCN Circ. 42013; triangulation location with Insight-HXMT/HE and Fermi/GBM: Zhang et al., GCN Circ. 42019) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 00:21:23.82 UTC on 26 September 2025 (https://cgbm.calet.jp/cgbm_trigger/flight/1442880852/index.html). The burst signal was seen by only the SGM detector.

The burst light curve shows a single pulse that starts at T+0.75 sec, peaks at T+1.08 sec, and ends at T+1.35 sec. The T90 and T50 durations measured by the SGM data are 0.55 +/- 0.11 sec and 0.25 +/- 0.10 sec (40-1000 keV), respectively.

The ground-processed light curve is available at

https://cgbm.calet.jp/cgbm_trigger/ground/1442880852/

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

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