TITLE:   GCN CIRCULAR
NUMBER:  23573
SUBJECT: GRB 181225A: CALET Gamma-Ray Burst Monitor detection
DATE:    18/12/28 05:46:14 GMT
FROM:    Valentin Pal'shin at AGU  <val@phys.aoyama.ac.jp>

V. Pal'shin, A. Yoshida, T. Sakamoto, S. Sugita (AGU), Y. Kawakubo (LSU),
A. Tezuka, S. Matsukawa, H. Onozawa, T. Ito, H. Morita, Y. Sone (AGU),
K. Yamaoka (Nagoya U), S. Nakahira (RIKEN), I. Takahashi (IPMU),
Y. Asaoka, S. Ozawa, S. Torii (Waseda U),
Y. Shimizu, T. Tamura (Kanagawa U),
W. Ishizaki (ICRR), M. L. Cherry (LSU),
S. Ricciarini (U of Florence),
A. V. Penacchioni, P. S. Marrocchesi (U of Siena),
and the CALET collaboration:

The hard GRB 181225A (AGILE/MCAL detection: Ursi et al., GCN Circ. 23560;
Fermi-LAT detection: Arimoto et al., GCN Circ. 23561;
Fermi GBM detection: Poolakkil et al., GCN Circ. 23562)
triggered the CALET Gamma-ray Burst Monitor (CGBM) at 11:44:11.011 UTC
on 25 December 2018. The burst signal was seen by all CGBM detectors.

The burst light curve shows the initial hard pulse which starts
at T-0.6 sec and ends at T+1.1 sec, followed by a weaker and softer tail
seen up to T+10.8 sec.
The T90 and the T50 durations measured by the SGM data are
10.6 +- 0.8 sec and 7.5 +- 0.8 sec (40-1000 keV), respectively.

The ground processed light curve is available at

http://cgbm.calet.jp/cgbm_trigger/ground/1229773383/

Although the measured durations put this GRB in the long class,
its hard initial pulse which has a duration of ~1.7 sec and
the weaker and softer tail may imply that this GRB is in fact
a short GRB with extended emission or it is similar to the famous
"long-short" GRB 060614 (Gehrels et al. 2006, Nature,
444, 1044: https://www.nature.com/articles/nature05376).

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