TITLE: GCN CIRCULAR NUMBER: 14698 SUBJECT: Konus-Wind observation of GRB 130521B DATE: 13/05/23 08:30:43 GMT FROM: Dmitry Frederiks at Ioffe Institute S. Golenetskii, R.Aptekar, D. Frederiks, E. Mazets, V. Pal'shin, P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline on behalf of the Konus-Wind team, report: The long-duration GRB 130521B (IPN triangulation: Hurley at al., GCN 14696) triggered Konus-Wind at T0=77073.510s UT (21:24:33.510). The light curve shows several pulses from ~T0 s to ~T0+20s, which, at its initial phase, form a quasi-periodic structure with the period of ~2.5s. The emission is seen up to ~7 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB130521_77073/ As observed by Konus-Wind, the burst had a fluence of (1.9 ± 0.15)x10-5 erg/cm2, and a 64-ms peak flux, measured from T0+0.512s, of (4.3 ± 0.3)x10-6 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum (measured from T0 to T0+22.016 s) is best fit in the 20 keV - 15 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.96 ± 0.07, the high energy photon index beta = -2.9 ± 0.3, the peak energy Ep = 151 ± 9 keV, chi2 = 97.6/97 dof. The spectrum at the maximum count rate (measured from T0 to T0+5.888 s) is best fit in the 20 keV - 15 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -0.69 ± 0.08, the high energy photon index beta = -3.6 ± 1.1, the peak energy Ep = 205 ± 12 keV, chi2 = 107/97 dof. For both spectra, we note a hint of counts excess over the model flux in the spectral channels around ~10 MeV. All the quoted results are preliminary.