TITLE: GCN CIRCULAR NUMBER: 9272 SUBJECT: GRB 090426: Swift/BAT spectral lag results DATE: 09/04/27 20:43:47 GMT FROM: Hans Krimm at NASA-GSFC T. N. Ukwatta (GWU/GSFC), N. Gehrels (GSFC), H. A. Krimm (CRESST/GSFC/USRA), T. Sakamoto (GSFC/UMBC), S. D. Barthelmy (GSFC), M. Stamatikos (GSFC/ORAU) (for the Swift-BAT team): For GRB 090426 (Cummings et al GCN 9254), the spectral lag analysis of the data from T-1 sec to T+2 sec yields a lag of -6 +/- 45 msec for the 25-50 to 50-100 keV bands using light curve binnings of 16, 32 and 64 msec. With redshift of 2.609 (Levesque et al GCN 9264) this lag value transforms to 1.7 +/- 12.5 ms in the GRB rest frame. The lag is consistent with zero but has relatively large uncertainty. Furthermore, the observed T90 (1.2 +/- 0.3 sec; Swift/BAT 15-350 keV, Sato et al., GCN 9263) and rest frame T90 (0.33 +/- 0.08 sec) values suggest a short-hard burst. However, the spectral fit to the BAT data (Sato et al., GCN 9263) indicates a relatively soft spectrum (a power-law fit to the spectrum gives index of 1.93 +/- 0.22). In summary, the observed and rest frame T90 values for GRB 090426 point strongly toward a short-hard burst classification. The spectral lag is consistent with zero, and the spectrum is marginally softer than typical for a short-hard burst. Our conclusion is that this burst could be either short or long, but the BAT data leads toward a classification as short.