[vsnet-grb-info 2564] GRB 051227: Further analysis of the Swift-BAT burst

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4401
SUBJECT: GRB 051227:  Further analysis of the Swift-BAT burst
DATE:    05/12/28 01:53:51 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <Scott at lheamail.gsfc.nasa.gov>

S. Barthelmy (GSFC), N. Gehrels (GSFC), J. Norris (GSFC),
T. Sakamoto (GSFC/NRC)
on behalf of the Swift-BAT team:

Continuing the analysis of GRB 051227, we point out the possibility
that this is a short burst.  We do not have the full data set downloaded
for this burst yet (only T-60 to T+120 sec), but we wish to get this
speculation out to the follow-up community to facilitate observations
as soon as possible (i.e. CA coast and Hawaii big glass).
We base this on 2 observations: 

1) The spectral lag is negligible, 2+-10 ms (1 sigma), between the
25-50 and 100-350 keV energy bands -- typical of spectral lags
in short bursts (Norris & Bonnell, submitted to ApJ).  The median lag
for long bursts is 50 ms, and only 1% of long bursts have a lag less than 2 ms.

2) The overall shape of the lightcurve of GRB 051227 is similar
to the lightcurve of the short hard burst GRB 050724.  The initial hard spike
is followed by 1 or 2 smaller short peaks at delays of one to several seconds.
Then a period of hiatus, followed by a broad low-level soft emission emission
that starts at a few tens of seconds out to 100+ seconds.  However, we can not
rule out that this is a FRED-like profile with a very long low-statistics
decay tail.