TITLE:   GCN CIRCULAR
NUMBER:  44966
SUBJECT: GRB 260616B: CALET Gamma-Ray Burst Monitor detection
DATE:    26/06/17 15:25:21 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), M. L. Cherry (LSU), S. Ricciarini (U of Florence),
P. S. Marrocchesi (U of Siena),
and the CALET collaboration:

The CALET Gamma-ray Burst Monitor (CGBM) detected GRB 260616B
at 07:05:24.65 UTC on 16 June 2026 (trigger #1465628601;
https://cgbm.calet.jp/cgbm_trigger/flight/1465628601/index.html).
A CGBM Notice was distributed in near real time.
This event was also reported by Fermi GBM (Preis et al., GCN #44951;
Malacaria et al., GCN #44953).

The burst signal was seen by HXM2 and SGM.  The burst light curve shows a double-peaked structure starting
at T-7.7 s, peaking at T+2.6 s, and ending at T+4.1 s.
The T90 and T50 durations measured with the SGM data are 11.2 +/- 0.3 s
and 8.1 +/- 0.2 s in the 40-1000 keV band, respectively.

Einstein Probe/WXT detected an X-ray transient, EP 260616a
(Li et al., GCN #44956), about 9 s before the CGBM trigger.
The position of EP 260616a was marginally above the Earth horizon
as seen from CALET/ISS at the trigger time, at an incident angle
of 110 degrees.

The ground-processed light curve is available at:
https://cgbm.calet.jp/cgbm_trigger/ground/1465628601/
The CALET data used in this analysis were provided by
the Waseda CALET Operation Center located at Waseda University.