TITLE: GCN CIRCULAR NUMBER: 12191 SUBJECT: Konus-Wind observation of GRB 110721A DATE: 11/07/22 09:48:51 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 bright hard long GRB 110721A (Fermi-GBM detection: Tierney and von Kienlin, GCN 12187; Fermi-LAT detection: Vasileiou et al., GCN 12188) triggered Konus-Wind at T0=17266.887s UT (04:47:46.887) The burst light curve shows a single FRED-like pulse with a total duration of ~25 s. The emission is seen up to ~10 MeV, a hard-to-soft spectral evolution is noticeable in the course of the event. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB110721_T17266/ As observed by Konus-Wind the burst had a fluence of (8.8 ± 0.9)x10-5 erg/cm2, and a 64-ms peak flux, measured from T0+1.984 s, of (2.3 ± 0.2)x10-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-integrated spectrum of the burst (measured from T0 to T0+26.624 s) can be fitted in the 20 keV - 10 MeV range by the GRB (Band) model, for which: the low-energy photon index alpha = -1.02 (-0.14, +0.16), the high energy photon index beta = -1.77 (-0.13, +0.07), the peak energy Ep = 393(-104, +199) keV, chi2 = 109.8/84 dof. The spectrum at the maximum count rate (measured from T0+0.256 to T0+2.304 s) is best fitted in the 20 keV - 10 MeV range by the GRB (Band) model, for which: the low-energy photon index alpha = -1.0 (-0.2, +0.2), the high energy photon index beta = -2.0 (-0.5, +0.2), the peak energy Ep = 1130(-490, +550) keV, chi2 = 74.1/74 dof. All the quoted results are preliminary. All the quoted errors are at the 90% confidence level.