TITLE: GCN CIRCULAR NUMBER: 22609 SUBJECT: Konus-Wind observation of GRB 180404B DATE: 18/04/06 13:33:29 GMT FROM: Dmitry Svinkin at Ioffe Institute D. Svinkin, S. Golenetskii, R. Aptekar, D. Frederiks, M. Ulanov, A. Tsvetkova, A. Lysenko, A. Kozlova, and T. Cline on behalf of the Konus-Wind team, report: The long-duration GRB 180404B (Swift-BAT detection: LaPorte et al., GCN Circ. 22590; Fermi-GBM observation: von Kienlin, GCN Circ. 22597) triggered Konus-Wind at T0=7898.049 s UT (02:11:38.049). The burst light curve shows the bright pulse which starts at ~T0-3.4 s and has a total duration of ~29 s followed by a weaker pulse seen up to ~T0+100 s. The emission is seen up to ~2 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB180404_T07898/ As observed by Konus-Wind, the burst had a fluence of 2.60(-0.16,+0.18)x10^-5 erg/cm2, and a 64-ms peak flux, measured from T0+8.832 s, of 2.07(-0.66,+0.66)x10^-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the burst (measured from T0 to T0+73.984 s) is best fit in the 20 keV - 5 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.65(-0.15,+0.16) and Ep = 205(-17,+21) keV (chi2 = 82/73 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.0 (chi2 = 82/72 dof). The spectrum near the maximum count rate (measured from T0+8.448 to T0+16.640 s) is best fit in the 20 keV - 5 MeV range by a power law with exponential cutoff model: with alpha = -0.19(-0.16,+0.17) and Ep = 186(-11,+12) keV (chi2 = 90/73 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -3.2 (chi2 = 90/72 dof). All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.