TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4975 SUBJECT: GRB 060418: Refined Analysis of the Swift-BAT burst DATE: 06/04/18 15:17:40 GMT FROM: Louis M Barbier at NASA/GSFC/Swift J. Cummings (GSFC/ORAU), L. Barbier (GSFC), S. Barthelmy (GSFC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (UMD), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD),D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/ORAU), G. Sato (ISAS), J. Tueller (GSFC), on behalf of the Swift-BAT team: Using the data set from T-119 to T+183 sec from the recent telemetry downlink, we report further analysis of BAT GRB 060418 (trigger #205851) (Falcone, et al. GCN 4966). The BAT ground-calculated position is RA,Dec = 236.428, -3.642 deg {15h 45m 42.6s, -3d 38' 31.5"} (J2000) +- 0.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 30%. The mask-weighted lightcurve shows three overlapping peaks - a slow rise beginning at T-8 to a broad peak at T+10, a smaller peak at T+18, followed by the largest spike at T+27. There is a small bump in the lightcurve at T+130 which coincides with a flare seen in the XRT data. (Falcone et al. GCN 4973). T90 (15-350 keV) is 52 +- 1 s. The time-averaged spectrum from T-19.2 to T+136.6 is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.66 +- 0.05. The fluence in the 15-150 keV band is 8.1 +- 0.2 x 10-06 erg/cm2. The 1-sec peak photon flux measured from T+27.45 sec in the 15-150 keV band is 6.7 +- 0.4 ph/cm2/sec. Eiso is 5.3e+52 ergs in the 37.35 - 373.5 keV range at the GRB rest frame using z = 1.49 (Dupree et al. GCN 4969, Vreeswijk et al. GCN 4974). All the quoted errors are at the 90% confidence level.