TITLE: GCN CIRCULAR NUMBER: 23061 SUBJECT: Konus-Wind observation of the bright nearby GRB 180728A DATE: 18/07/30 12:21:03 GMT FROM: Dmitry Frederiks at Ioffe Institute D. Frederiks, S. Golenetskii, R.Aptekar, A. Kozlova, A.Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report: The long, very bright GRB 180728A (Swift-BAT detection: Starling et al., GCN 23046; Fermi-GBM detection: Veres et al., GCN 23053) triggered Konus-Wind (KW) at T0=62954.093 s UT (17:29:14.093). The burst light curve shows a smooth pulse with a total duration (T100) of ~17 s. The emission is seen up to ~10 MeV. As observed by Konus-Wind, the burst had a fluence of (5.14 ± 0.29)x10^-5 erg/cm2 and a 64-ms peak energy flux, measured from T0+15.168, of (1.94 ± 0.15)x10^-5 erg/cm2 (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum (measured from T0 to T0+19.2 s) is best fit in the 30 keV - 15 MeV range by the GRB (Band) function with the following model parameters: the low-energy photon index alpha = -1.48 (-0.10,+0.12), the high energy photon index beta = -2.57 (-0.18,+0.12), the peak energy Ep = 97 (-6,+7) keV, chi2 = 94/96 dof. The spectrum near the peak count rate (measured from T0+1.280 s to T0+1.792 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 = -1.44 (-0.15,+0.15), the high energy photon index beta = -2.81 (-1.44,+0.24), the peak energy Ep = 127 (-13,+18) keV, chi2 = 54/56 dof. Assuming the redshift z=0.117 (Rossi et al., GCN 23055) and a standard cosmology with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315, and Omega_Lambda = 0.685 (Planck Collaboration, 2014), we estimate the following rest-frame parameters: the isotropic energy release E_iso is (2.33 ± 0.10)x10^51 erg, the peak luminosity L_iso is (9.51 ± 0.58)x10^50 erg/s (both in the 1-10000 keV rest-frame band). The rest-frame peak energy of the time-integrated spectrum, Epi,z, is 108(-7, 8) keV, and the rest-frame peak energy of the 'peak' spectrum, Epp,z, is 142(-15, 20) keV. With these energetics, the burst lies on the upper edges of 68% prediction bands for both 'Amati' and 'Yonetoku' relations built for the sample of 138 long KW GRBs with known redshifts (Tsvetkova et al., ApJ 850 161, 2017). The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB180728_T62954/ All the quoted errors are estimated at the 90% confidence level. All the presented results are preliminary.