[vsnet-grb-info 5081] GRB 070809: The Swift evidence for the SHB nature of this burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6788
SUBJECT: GRB 070809: The Swift evidence for the SHB nature of this burst
DATE:    07/09/13 21:00:38 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at lheamail.gsfc.nasa.gov>

S.D. Barthelmy (GSFC), T. Sakamoto (GSFC), J. Norris (SLAC), N. Gehrels (GSFC)
report:

GRB 070809 (Marshall GCN 6728 and Krimm GCN 6732) is very likely
a short burst.  We base this on four results:

1) The spectral lag in 25-50 to 100-350 keV bands is consistent with zero:
+11 ms +38-61 ms for 8 ms binning.

2) The T90 was 1.3 +- 0.1 sec which is in the 'short' range
of BAT burst durations (see figure 9 of the BAT1 catalog paper; Sakamoto et al.,
accepted in ApJS, arXiv:0707.4626)

3) The fluence hardness ratio S(50-100 keV)/S(25-50 keV) is 
1.24 +- 0.27 (90% error), which is consistent with the BAT short GRB
population (see figure 10 of the BAT1 catalog paper; Sakamoto et al., 
accepted in ApJS, arXiv:0707.4626).   

4) The XRT light curve showed a flat phase often seen with long bursts. 
However, some short bursts also have such a phase (GRB 050724 and 051221A).