TITLE: GCN CIRCULAR NUMBER: 14392 SUBJECT: GRB 130418A, Swift-BAT refined analysis DATE: 13/04/19 13:49:19 GMT FROM: Hans Krimm at NASA-GSFC J. R. Cummings (GSFC/UMBC), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), M. De Pasquale (UCL-MSSL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (NASA/GSFC/ORAU),C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (MSU) (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 130418A (trigger #553847) (De Pasquale, et al., GCN Circ. 14377). The BAT ground-calculated position is RA, Dec = 149.045, 13.674 deg which is RA(J2000) = 09h 56m 10.8s Dec(J2000) = +13d 40' 28.2" with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment). The partial coding was 89%. It appears that BAT triggered on the decay phase of a burst already in progress when the source position came into the BAT field of view during a pre-planned slew. Therefore we do not know the true time of the start of the burst, but it was at least 50 seconds before T0, here defined as the trigger time. From T-50 sec, when the burst became visible, there is a steady decline punctuated by two peaks at approximately T-20 and T+50, the first being harder than the second. The decay continued to roughly T+300 sec. The burst location was no longer visible after T+450, when another slew took it out of the BAT field. T90 cannot be determined since BAT did not see the start of the burst, but T90 is at least 300 seconds. The time-averaged spectrum from T-40.16 to T+285.59 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.07 +- 0.17. The fluence in the 15-150 keV band is 1.8 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T-37.68 sec in the 15-150 keV band is 0.6 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. Note that these values are calculated only for the part of the burst detected by the BAT, so the fluence should be considered a lower limit. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/553847/BA/