[vsnet-grb-info 25560] SGR Atel

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  27660
SUBJECT: SGR Atel
DATE:    20/04/28 02:36:54 GMT
FROM:    David Palmer at LANL  <dmopalmer at gmail.com>

Comments?

Author list?

A place to put plots?

David M. Palmer (LANL)

rest of author list

on behalf of the BAT Team,


A Forest of Bursts from SGR 1935+2154

At 18:26:20 of 2020-04-27 UT, the Swift Burst Alert Telescope (BAT) 
triggered and located a burst from the Soft Gamma Repeater 
SGR 1935+2154 (Trigger #968211). (GCN #27657; Barthelmy et al.)

This initial burst was followed by an intense sequence of
bursts starting at ~T+300s after the first trigger time.  
This includes separate time segments, 3 seconds and 15 seconds 
long, made up of multiple bursts during which the count rate
never returns to baseline on the 64 ms timescale (the highest 
resolutiondata that has been downlinked so far).  

During those time intervals, the peak count rate reaches up to
130k counts/s on a 64 ms timescale over 15-350 keV band, and
350k counts/s on a 1 second timescale over the full detector
sensitivity range.  (The majority of these additional counts 
would be below the 15 keV calibrated energy bin but above
the Low-Level-Discriminator level which varies from
detector-to-detector in BAT's 32k-element array, but
which is typically 12-14 keV.  This indicates that the
emission is very soft.)

During the first 24 minutes of the episode, there were at least 
35 clearly-distinguishable bursts outside of the piled-up time 
intervals.  Bursts have also been seen by other instruments,
including Fermi/GBM and CALET and continue, at a lower rate,
to at least the time of this writing ~T+8 hours.

This is similar to the forest of bursts seen on 2008-05-28 
with the re-activation of SGR 1627-41.  (GCN #7777; Palmer et al)

SGR 1935+2154's recent activation was first detected by a burst
5 days earlier, which was seen by multiple spacecraft,
providing timing information that determined the source
(GCN #27625; Hurley et. al).  The previous BAT detection
was 9 bursts in ~24 hours in November 2019.




David Palmer
dmopalmer at gmail.com <mailto:dmopalmer at gmail.com>