[vsnet-grb-info 25563] high bursting activity of SGR 1935+2154: CGBM observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  27663
SUBJECT: high bursting activity of SGR 1935+2154: CGBM observations
DATE:    20/04/28 06:45:35 GMT
FROM:    Valentin Pal'shin at AGU  <val at phys.aoyama.ac.jp>

S. Ricciarini (U of Florence),
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), M. L. Cherry (LSU),
P. S. Marrocchesi (U of Siena),
and the CALET collaboration:

The CALET Gamma-ray Burst Monitor (CGBM) has been observing
high bursting activity of SGR 1935+2154 since the CGBM trigger
at ~18:32 UTC on 27 April 2020.
No real-time CGBM GCN notice was distributed about this trigger because
the real-time communication from the ISS was off (loss of signal).
This trigger followed the Swift and Fermi-GBM triggers on bursts
from SGR 1935+2154 at ~18:20 UTC reported in GCNs 27657, 27659, and 27660
(at this time CGBM HV was off).
The CGBM data display a burst cluster along with multiple
short bright bursts.

The first CGBM trigger was shortly followed by another CGBM trigger at
18:46:08.675 UTC (trigger 1272047979:
http://cgbm.calet.jp/cgbm_trigger/flight/1272047979/index.html)
with several intense bursts.

Additional two unalerted CGBM triggers with multiple short intense soft
bursts were detected at ~20:15 UTC and ~21:49 UTC on 2020-04-27.
After this, CGBM on-board trigger was disabled because it reached the
maximum numbers of the accepted triggers.

Further episodes of SGR activity were observed in CGBM TH data at
~23:18 UTC on 2020-04-27 and at ~00:43 - 00:57 UTC on 2020-04-28.

Totally several tens of short bright SGR bursts have been detected by CGBM
so far. So, SGR 1935+2154 did enter a new phase of activity
as was suggested in GCN 27623.