TITLE: GCN CIRCULAR NUMBER: 10615 SUBJECT: GRB 100418A: Swift-BAT refined analysis DATE: 10/04/19 01:00:52 GMT FROM: Scott Barthelmy at NASA/GSFC T. N. Ukwatta (GWU) S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC) (i.e. the Swift-BAT team): Using the data set from T-61 to T+242 sec from recent telemetry downlinks, we report further analysis of BAT GRB 100418A (trigger #419797) (Marshall, et al., GCN Circ. 10612). The BAT ground-calculated position is RA, Dec = 256.358, 11.457 deg, which is RA(J2000) = 17h 05m 25.8s Dec(J2000) = +11d 27' 26.8" with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment). The partial coding was 49%. The mask-weighted light curve shows two overlapping peaks starting at ~T-10 sec, peaking at ~T+2 sec, and ending at ~T+40 sec. T90 (15-350 keV) is 7.0 +- 1.0 sec (estimated error including systematics). The time-averaged spectrum from T-1.1 to T+7.8 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.16 +- 0.25. The fluence in the 15-150 keV band is 3.4 +- 0.5 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T+0.47 sec in the 15-150 keV band is 1.0 +- 0.2 ph/cm2/sec. 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/419797/BA/