[AAVSO-HEN] GRB 090309, Swift-BAT lag analysis

[grb at aavso.org]

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TITLE:   GCN CIRCULAR
NUMBER:  8982
SUBJECT: GRB 090309, Swift-BAT lag analysis
DATE:    09/03/13 09:58:16 GMT
FROM:    Takanori Sakamoto at NASA/GSFC  <takanori.sakamoto-1 at nasa.gov>

T. Sakamoto (GSFC/UMBC), J. P. Norris, T. N. Ukwatta (GWU/GSFC),  
S. D. Barthelmy (GSFC), N. Gehrels (GSFC), M. Stamatikos (GSFC/ORAU)  
(for the Swift-BAT team): 
 
For GRB 090309 (Evans et al. GCN Circ. 8964), we are unable to determine  
if this is a short or long burst.  The reasons are as follows:  (1) the  
spectral lag is 0.044 +/- 0.16 sec (between the 50-100 and 15-25 keV).   
(2) The T90 duration is 3.0 +- 1.4 sec (Palmer et al. GCN Circ. 8967)
which is midway between the two T90 distributions.  (3) The photon index 
is 1.36 +/- 0.33 (Palmer et al. GCN Circ. 8967) is also in the middle of 
the short and hard distributions (Figure 13 of Sakamoto et al., ApJS, 175, 179).