TITLE: GCN CIRCULAR NUMBER: 12477 SUBJECT: GRB 111020A Spectral lag analysis DATE: 11/10/22 20:25:56 GMT FROM: Takanori Sakamoto at NASA/GSFC T. Sakamoto (GSFC/UMBC), S. D. Barthelmy (GSFC), J. Norris (BSU), T. N. Ukwatta (MSU) We report the spectral lag analysis for GRB 111020A (GCN Circ. 12460) based on the BAT data. Using 64 ms binned light curves, the spectral lag for 15-25 keV to 50-100 keV is 124 +36/-38 msec. This significant lag is due to a broader pulse in the 15-25 keV band comparing to that in the 50-100 keV band which indicates the strong pulse evolution from hard to soft. Although the burst duration itself is short (T90 = 400 ms; GCN Circ. 12464), this positive lag argues against a "short" classification. However, there is a possibility that the broader pulse seen in the 15-25 keV band is composed from two pulses instead of a single pulse. If this is the case, the lag result above could be confused by cross-correlating the 2nd pulse in the 15-25 keV and the 1st pulse in the 50-100 keV band. Due to the limiting signal-to-noise in the light curve data, it is not possible to claim whether the broad pulse in the 15-25 keV has two pulses or just a single pulse. Give the large non-zero lag and the possible double peak interpretation that could cause a false lag, we think it equally like that this burst is short or long. [GCN OPS NOTE(24oct11): Per author's request, the T90 value typo was corrected to 400 ms.]