TITLE:   GCN CIRCULAR
NUMBER:  39021
SUBJECT: GRB 250121A: CALET Gamma-Ray Burst Monitor detection
DATE:    25/01/24 14:43:22 GMT
FROM:    Yuta Kawakubo at Aoyama Gakuin University <kawakubo@phys.aoyama.ac.jp>

T. Sakamoto, A. Yoshida, 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), S. Ricciarini (U of Florence),
P. S. Marrocchesi (U of Siena),
and the CALET collaboration:

The long GRB 250121A (Fermi GBM Final Real-time Localization: Fermi GBM team, GCN Circ. 39006;
Fermi-LAT detection: Holzmann Airasca et al., GCN Circ. 39010;
INTEGRAL/SPI-ACS detection: Barria et al., GCN Circ. 39011;
Fermi GBM Observation: Godwin et al., GCN Circ. 39018;
) was detected in the ground analysis of the CALET Gamma-ray 
Burst Monitor (CGBM) data around 23:36:05.78 on 21 January 2025 (referenced
to the Fermi-GBM Observation: GCN Circ. 39018).
(https://cgbm.calet.jp/cgbm_trigger/flight/1421537655/index.html).
The burst signal was seen by only the SGM detector. 

The burst light curve shows a double-peaked structure that starts
at T+0.1 sec, peaks at T+0.7 sec, and ends at T+5.4 sec.
The T90 and T50 durations measured by the SGM data are 4.7 +/- 0.2 sec
and 2.6 +/- 0.4 sec (40-1000 keV), respectively.

The ground-processed light curve is available at

https://cgbm.calet.jp/cgbm_trigger/ground/1421537655/

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