TITLE: GCN CIRCULAR NUMBER: 15260 SUBJECT: Konus-Wind observation of GRB 130925A DATE: 13/09/26 15:36:02 GMT FROM: Dmitry Frederiks at Ioffe Institute S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin, P. Oleynik, M. Ulanov, D. Svinkin, and T. Cline, on behalf of the Konus-Wind team, report: The very long GRB 130925A (Swift-BAT trigger #571830: Lien et al., GCN 15246; Markwardt et al., GCN 15257; MAXI/GSC detection: Suzuki et al., GCN 15248; Fermi/GBM detection: Fitzpatrick, GCN 15255; INTEGRAL/SPI-ACS observation: Savchenko et al., GCN 15259) was detected by Konus-Wind in the waiting mode. The light curve shows several multi-peaked pulses separated by long periods of a low-level emission with a total duration of ~4500 s. At least three major emission episodes can be distingushed: the first one, which triggered BAT, started at ~T0(BAT)-130 s and lasted until ~T0(BAT)+170 s; the second, more fluent episode, from ~T0(BAT)+1750 s to ~T0(BAT)+2950 s; and the third, the weakest one, which onset corresponds to the MAXI detection, from ~T0(BAT)+3730 s to ~T0(BAT)+4360 s. The possible precursor detected by GBM is clearly seen at ~T0(BAT)-900 s in the softest KW energy band. As observed by Konus-Wind, the burst had a fluence of (5.0 ± 0.1)x10^-4 erg/cm2 and a 2.944-s peak energy flux, measured from T0(BAT)+2548.858, of (1.0 ± 0.03)x10^-6 erg/cm2 (both in the 20 - 10000 keV energy range). The emission shows no signs of strong spectral variability. Modeling the KW 3-channel time-integrated spectrum (from T0(BAT)-120 s to T0(BAT)+4340 s) by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) yields alpha = -1.42 ± 0.04, and Ep = 181 ± 10 keV. Assuming z = 0.347 (Vreeswijk et al., GCN 15249) and a standard cosmology model with H_0 = 71 km/s/Mpc, Omega_M = 0.27, Omega_Lambda = 0.73, the isotropic energy release E_iso = (1.50 ± 0.03)x10^53 erg, the peak isotropic luminosity L_iso = (4.0 ± 0.1)x10^50 erg, and Ep_rest is 244 ± 13 keV. Thus, the prompt gamma-ray emission properties of this GRB: fluence, Ep, and E_iso are similar to those observed in other long energetic GRBs; the only outstanding feature of the burst is its huge duration. In that, it resembles other ultra-long bursts: GRB 111209A at z=0.677 (with total duration of ~10000 s: Golenetskii et al., GCN 12663) and GRB 121027A at z=1.77 (with a total duration of >4000 s: Starling et al., in preparation). Therefore, we suggest that the extremely rapid and dramatic X-ray flaring observed over the first 10^4 s after the BAT trigger (Evans et al., GCN 15254) at least partially corresponds to the burst prompt emission. All the quoted errors are estimated at the 1 sigma confidence level. All the presented results are preliminary. The K-W light curve of this burst is available at http://www.ioffe.rssi.ru/LEA/GRBs/GRB130925A/