TITLE:   GCN CIRCULAR
NUMBER:  32575
SUBJECT: Konus-Wind detection of GRB 220921A
DATE:    22/09/22 18:47:23 GMT
FROM:    Dmitry Svinkin at Ioffe Institute  <svinkin@mail.ioffe.ru>

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

The bright, long-duration GRB 220921A
(Fermi-LAT detection: Pillera et al., GCN Circ. 32568;
Fermi-GBM detection: Bissaldi, GCN Circ. 32574)
triggered Konus-Wind at T0=39961.714 s UT (11:06:01.714).

The burst light curve shows the bright multipeaked initial
emission episode which starts at ~T0-3.7 s and ends at ~T0+38 s, 
followed by a weaker episode at T0+220 s.
The total duration of ~231 s.
The emission is seen up to ~8 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB220921_T39961/

As observed by Konus-Wind, the burst
had a fluence of 9.71(-2.95,+2.35)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+9.216 s,
of 1.44(-0.25,+0.26)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+257.536 s)
is best fit in the 20 keV - 8 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.88(-0.47,+0.67),
the high energy photon index beta = -2.07(-0.50,+0.15),
the peak energy Ep = 126(-36,+85) keV
(chi2 = 93/78 dof).

The spectrum near the maximum count rate
(measured from T0+6.656 to T0+11.776 s)
is best fit in the 20 keV - 8 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.89(-0.14,+0.20),
the high energy photon index beta = -2.26(-0.19,+0.14),
the peak energy Ep = 203(-35,+36) keV
(chi2 = 106/78 dof).

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