GCN Circular 31719

P. S. Marrocchesi (U of Siena),
A. Yoshida, T. Sakamoto, V. Pal'shin, S. Sugita (AGU),
Y. Kawakubo (LSU), K. Yamaoka (Nagoya U), S. Nakahira (RIKEN),
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),
and the CALET collaboration:

At 05:35:27.809 UTC on 8 March 2022, the CALET Gamma-ray Burst Monitor
(CGBM) triggered on a long weak GRB followed in ~460 s by the bright
GRB 220308A, localized by the IPN (Svinkin et al., GCN 31715
Not found
 
 
;
https://gcn.gsfc.nasa.gov/other/220308A.gcn3
Not found
 
 
).
Both bursts were seen by all CGBM detectors.
The first (trigger) burst might be a precursor of GRB 220308A.

The trigger burst light curve shows a double-peaked pulse which starts at
T+1.9 sec, peaks at T+3.6 sec,and ends at T+15.0 sec. The T90 and T50
durations measured by the SGM data are 11.6 +- 1.6 sec and 7.4 +- 1.6 sec
(40-1000 keV), respectively.
The GRB 220308A light curve shows a multi-peaked structure which starts
at T+461.6 sec, peaks at T+465.9 sec, and ends at T+481.9 sec.
The T90 and T50 durations measured by the SGM data are 15.4 +- 0.4 sec
and 4.0 +- 0.1 sec (40-1000 keV), respectively.

The ground processed light curve is available at

http://cgbm.calet.jp/cgbm_trigger/ground/1330752907/

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