TITLE: GCN CIRCULAR NUMBER: 10660 SUBJECT: GRB 100420A: Swift-BAT refined analysis DATE: 10/04/23 17:31:00 GMT FROM: Scott Barthelmy at NASA/GSFC J. R. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), D. M. Palmer (LANL), A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-205 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 100420A (trigger #419932) (Baumgartner, et al., GCN Circ. 10628). The BAT ground-calculated position is RA, Dec = 296.090, 55.755 deg, which is RA(J2000) = 19h 44m 21.5s Dec(J2000) = +55d 45' 18.7" with an uncertainty of 4.6 arcmin, (radius, sys+stat, 90% containment). The partial coding was 92%. The mask-weighted light curve shows a single peak starting around T-10 sec, peaking at ~T+10 sec, and ending at ~T+60 sec. T90 (15-350 keV) is 48 +- 36 sec (estimated error including systematics). The time-averaged spectrum from T-30 to T+70 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.17 +- 0.22. The fluence in the 15-150 keV band is 5.7 +- 1.0 x 10^-7 erg/cm2. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/419932/BA/