[vsnet-grb-info 25523] bright SGR burst detected by CALET Gamma-Ray Burst Monitor

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  27623
SUBJECT: bright SGR burst detected by CALET Gamma-Ray Burst Monitor
DATE:    20/04/22 14:57:11 GMT
FROM:    Valentin Pal'shin at AGU  <val at phys.aoyama.ac.jp>

M. L. Cherry (LSU),
A. Yoshida, T. Sakamoto, V. Pal'shin, S. Sugita (AGU),
Y. Kawakubo (LSU), K. Yamaoka (Nagoya U), S. Nakahira (RIKEN),
Y. Asaoka, S. Torii (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U),
N. Cannady (GSFC/UMBC), S. Ricciarini (U of Florence),
P. S. Marrocchesi (U of Siena),
and the CALET collaboration:

At 08:53:17.656 UTC on 22 April 2020, the CALET Gamma-ray Burst Monitor
(CGBM) triggered on a very bright SGR-like burst (trigger 1271580418:
http://cgbm.calet.jp/cgbm_trigger/flight/1271580418/index.html).
The burst signal was seen by all CGBM detectors.

This burst is also clearly seen by the publicly available
INTEGRAL SPI-ACS light curve.

The CGBM light curve shows a bright pulse with a duration of about 0.6 sec.
The emission is seen up to ~170 keV.

The estimated time delay between CGBM and INTEGRAL-SPI-ACS is consistent
with the expected propagation time delay for the position of SGR 1935+2154,
from which a bright burst has been recently observed
(Svinkin et al., GCN Circ. 27527, Veres et al., GCN Circ. 27531,
Ridnaia et al., GCN Circ. 27554).
At the trigger time, this SGR was above the horizon and in the FOVs of
the CGBM detectors. At the same time, it was below the horizon for Fermi
and above the horizon, but outside the coded FOV of Swift-BAT,
that is consistent with the non-triggering by these facilities.

Hence, we conclude that this bright burst is likely originated from
SGR 1935+2154 which may be entering a new active phase.

The results of the further analysis will be reported upon arrival of
the burst event data.

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