[AAVSO-HEN] Further Swift-BAT analysis of GRB 071227

[grb at aavso.org]

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TITLE:   GCN CIRCULAR
NUMBER:  7156
SUBJECT: Further Swift-BAT analysis of GRB 071227
DATE:    07/12/28 20:22:04 GMT
FROM:    Takanori Sakamoto at NASA/GSFC  <Taka.Sakamoto at nasa.gov>

T. Sakamoto (GSFC/UMBC), J. Norris (NASA/Ames), T. Ukwatta (GWU), 
S. D. Barthelmy (GSFC), N. Gehrels (GSFC), M. Stamatikos (GSFC/ORAU) 

We further report about the additional analysis of the spectral 
lag and the extended emission for a possible short GRB 071227.  
Now, we believe GRB 071227 is very likely a short GRB based on 
following the BAT prompt emission properties.  

1) The spectral lag in 25-50 to 100-350 keV bands is consistent with 
zero, 0.4 ms +- 14 ms, for 8 ms binning.  

2) T90 of the initial spike is 1.8 +- 0.4 sec (Sato et al., GCN 7148) 
which is in the 'short' range of the BAT burst duration (see figure 9 
of the BAT1 catalog paper; Sakamoto et al., ApJS in press, arXiv:0707.4626).  

3) We found a hint of the extended emission up to T+~100 sec 
(Norris et al., ApJ, 643, 266).  Although the significance in the image 
domain is ~4 sigma (15-25 keV), we think this emission is associated with 
the GRB because of no bright hard X-ray source in the BAT field of view 
after the spacecraft slew which could be a source of a weak extended emission.