TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4989 SUBJECT: Konus-Wind observation of GRB 060418 DATE: 06/04/21 12:27:00 GMT FROM: Valentin Pal'shin at Ioffe Inst S. Golenetskii, R.Aptekar, E. Mazets, V. Pal'shin, D. Frederiks, M. Ulanov, and T. Cline on behalf of the Konus-Wind team report: The long GRB 060418 (Swift-BAT trigger=205851; Falcone et al. GCN 4966; Cummings et al. GCN 4975) was observed by Konus-Wind in the waiting mode. The emission is clearly seen in the three K-W bands: G1 (18-70 keV), G2 (70-360 keV) and G3 (360-1360 keV) with high S/N. Using an approximation the time-integrated 3-channel K-W spectrum by a power law with exponential cutoff model: dN/dE ~ E^(-alpha)*exp(-E*(2-alpha)/Ep), we have found alpha ~1.5, and Ep ~230 keV. As observed by Konus-Wind, the burst had a duration of ~44 s, and fluence ~1.6x10^-5 erg/cm2 (in the 20 - 1100 keV energy range). Assuming z = 1.49 (Dupree et al. GCN 4969; Vreeswijk and Jaunsen GCN 4974) and a standard cosmology model with H_0 = 70 km/s/Mpc, Omega_M = 0.3, Omega_\Lambda = 0.7, the isotropic energy release is E_iso ~9x10^52 erg. ~1200 s after the BAT GRB 060418, Konus-Wind detected another burst. Whether the second event relates to the first GRB or whether it is a different GRB detected by chance close to first one is not clear at this time. The available data cannot confirm or rule out the possibility that the second event came from the same location as the Swift GRB: a) the Konus-Wind ecliptic latitude response for the second event is consistent with the ecliptic latitude response for the Swift GRB. b) BAT does not see a rate increase at ~03:26. At this time, GRB 060418 was out of the BAT FOV (~57 degrees off axis), but a little above the Earth horizon (J. Cummings, private communication). So, the BAT data do not rule out the possibility the second event came from GRB 060418. c) Neither burst was detected by Odyssey, but both bursts are Mars-blocked, if the second one comes from the same direction as the first. RHESSI observed the first (Swift) burst, but not the second one. The RHESSI detection of the first burst was rather weak, and as observed by Konus, the second burst was weaker than the first one, so it could have missed. the second one (K. Hurley, private communication). d) The second event was not detected by Suzaku-WAM. The position of GRB 060418 was occulted by the Earth from Suzaku at the time of the second event (K. Yamaoka, private communication). Hence, the situation is ambiguous. Possibly, the data from optical telescopes can clarify this issue, if there were some optical observations of the GRB 060418 afterglow during the time of the second event. The K-W light curves of these events are available at http://www.ioffe.rssi.ru/LEA/GRBs/GRB060418/