TITLE: GCN CIRCULAR NUMBER: 9083 SUBJECT: Konus-Wind observation of GRB 090401B DATE: 09/04/03 11:35:30 GMT FROM: Valentin Pal'shin at Ioffe Inst S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf of the Konus-Wind team, report: The long bright GRB 090401B (Swift-BAT trigger #348152: Schady et al., GCN 9066; Stamatikos et al., GCN 9068) triggered Konus-Wind at T0=30922.964 s UT (08:35:22.964). The burst light curve shows a multipeaked structure with a duration of ~11 s. There is a hint of an extended soft emission. As observed by Konus-Wind the burst had a fluence of 6.25(-0.75, +0.78)x10^-5 erg/cm2, and a 16-ms peak flux measured from T0+6.576 s of 4.63(-0.86, +0.87)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the burst (from T0 to T0+16.996 s) is well fitted (in the 20 keV - 10 MeV range) by GRB (Band) model for which: the low-energy photon index alpha = -0.78(-0.09, +0.11), the high energy photon index beta = -2.14(-0.23, +0.15), the peak energy Ep = 409(-60, +66) keV (chi2 = 61.8/85 dof). All the quoted errors are at the 90% confidence level. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB090401_T30922/