Konus-Wind detection of GRB 240918B

The long-duration GRB 240918B (Fermi-GBM detection: The Fermi GBM team, GCN 37558; INTEGRAL SPI-ACS detection: Pawar, GCN 37560; AstroSat CZTI detection: Joshi et al., GCN 37588; IPN triangulation: Kozyrev et al., GCN 37602) triggered Konus-Wind at T0=75415.787 s UT (20:56:55.787). The burst light curve shows a multipeaked structure which starts at ~T0-1.9 s and has a total duration of ~4.4 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/GRB240918_T75415/ As observed by Konus-Wind, the burst had a fluence of 4.19(-0.60,+0.71)x10^-6 erg/cm2, and a 64-ms peak flux, measured from T0+1.264 s, of 2.56(-0.89,+0.93)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+8.448 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.49(-0.44,+0.56) and Ep = 173(-28,+45) keV (chi2 = 112/99 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.2 (chi2 = 111/98 dof). All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.