TITLE: GCN CIRCULAR NUMBER: 32600 SUBJECT: Konus-Wind detection of GRB 220927A DATE: 22/09/29 20:38:34 GMT FROM: Anna Ridnaia at Ioffe Institute ridnaia@mail.ioffe.ru

A.Ridnaia, D. Frederiks, A.Lysenko, D. Svinkin, A. Tsvetkova, M. Ulanov, and T. Cline, on behalf of the Konus-Wind team, report:

The long-duration GRB 220927A (Fermi-GBM detection: Fermi GBM Team, GCN 32594; IPN triangulation: Kozyrev et al., GCN 32597) triggered Konus-Wind at T0=20180.364 s UT (05:36:20.364).

The burst light curve shows a multipeaked initial emission episode which starts at ~T0-1.9 s and ends at ~T0+8.3 s, followed by a weaker episode at ~T0+35 s. The total burst duration is ~46.7 s. The emission is seen up to 2 MeV.

The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB220927_T20180/

As observed by Konus-Wind, the burst had a fluence of 4.18(-1.08,+1.60)x10^-6 erg/cm2, and a 64-ms peak flux, measured from T0+3.968 s, of 9.37(-2.57,+2.78)x10^-7 erg/cm2/s (both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum of the burst (measured from T0 to T0+41.216 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -1.37(-0.77,+2.06), the high energy photon index beta = -2.60(-7.40,+0.35), the peak energy Ep = 40(-22,+15) keV, chi2 = 93/96 dof.

The spectrum near the maximum count rate (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.97(-0.43,+0.61), the high energy photon index beta = -3.04(-6.96,+0.44), the peak energy Ep = 48(-6,+6) keV, chi2 = 83/94 dof.

All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.