TITLE: GCN CIRCULAR NUMBER: 10567 SUBJECT: GRB 100401A Burst, possibly short, detected in ground analysis of BAT data DATE: 10/04/02 19:57:49 GMT FROM: Jay R. Cummings at NASA/GSFC/Swift J. R. Cummings (GSFC/UMBC), N. Gehrels (NASA/GSFC), F. E. Marshall (NASA/GSFC) on behalf of the Swift team At 2010-04-01T07:07:31.9 BAT detected a rate increase (trigger# 417974). The source was found with insufficient significance onboard to trigger an automated burst response. A significant source was found in ground analysis at RA, Dec 290.813, -8.257, which is: RA (J2000) 19h 23m 15.5s Dec (J2000) -08d 15' 25" with an estimated uncertainty of 2 arcmin radius (90% containment). The source was 10% coded in the BAT field of view. As seen in BAT, the burst had a single square-shaped pulse of about 2 seconds duration. The spectrum from 15 to 150 keV is best fit by a simple power law function with a photon index of 1.7 +- 0.2. We note that this is softer than is typical for "short, hard" GRBs. The fluence was (3.6 +- 1.2) erg/cm2. The 1-second peak flux was 2.4 photons/cm2. Since this burst was not detected with sufficient significance onboard, there are no automated data products. A Swift TOO is in progress.