TITLE: GCN CIRCULAR NUMBER: 9159 SUBJECT: GRB 090418B: Detection of a bright burst from Swift-BAT slew data DATE: 09/04/18 22:19:33 GMT FROM: Antonio Copete at Harvard U A. Copete, J. Grindlay (Harvard) S. Barthelmy, C. Markwardt, N. Gehrels (NASA/GSFC) We report the detection of a bright GRB by the BAT Slew Survey (BATSS) in the slew that started at 08:59:02 and lasted 151 sec. The ground- calculated position is RA, Dec = 225.910, +17.224 deg, which is RA (J2000) = 15h 03m 38s Dec(J2000) = +17d 13' 26" with an uncertainty of 1.91 arcmin (90% confidence, including systematics). The detection was triggered by simultaneous independent detections of 86.0 sigma and 41.8 sigma from imaging in the 15-50 keV and 50-150 keV energy bands, respectively. The burst mask-tagged lightcurve lightcurve in the 15-150 keV band shows a strong and broad multi-peaked emission structure starting at T+25sec as the burst enters the BAT field-of-view, lasting 48 sec, and peaking 6 times at T +29, T+35, T+38, T+47, T+58 and T+62sec. This is followed by a weaker broad peak starting at T+87sec, lasting 28sec and peaking at T+100sec. T90 = 65.0sec and T50 = 17.0sec. The time-averaged spectrum over the 120 sec exposure time of the source is best fit by a power law with an exponential cutoff, with photon index 1.42 and high-energy cut at 319 keV. The fluence in the 15-150 keV band is 1.6 x 10^-5 erg/cm^2, and the peak 1-sec flux is 6.5 x 10^-7 erg/cm^2/sec at T+38sec. A follow-up Swift ToO observation for this burst has been scheduled.