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 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).