GCN Circular 34659

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

The long GRB 230911D (Fermi GBM team, GCN 34656
Not found
 
 
)
triggered Konus-Wind (KW) at T0=28387.687 s UT (07:53:07.687).

The burst light curve shows a bright, multi-peaked emission complex,
which starts at ~T0-3 s, peaks at ~T0+15 s,
and has a total duration of ~60 s.
The emission is seen up to ~5 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB230911_T28387/

As observed by Konus-Wind, the burst had
a fluence of (1.57 ± 0.12)x10^-4 erg/cm^2 and
a 64-ms peak energy flux, measured from T0 + 14.848 s,
of (1.42 ± 0.15)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+54.272 s)
is best fit in the 20 keV - 15 MeV range
by a GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.74 (-0.06,+0.06),
the high energy photon index beta = -2.44 (-0.28,+0.17),
the peak energy Ep = 343 (-22,+23) keV,
chi2 = 126/96 dof.

The spectrum near the peak count rate (measured from T0+14.336 to T0+16.384 s)
is best fit in the 20 keV - 15 MeV range
by a GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.13 (-0.16,+0.18),
the high energy photon index beta = -2.56 (-0.32,+0.21),
the peak energy Ep = 405 (-43,+48) keV,
chi2 = 95/73 dof.

All the quoted errors are estimated at the 90% confidence level.
All the presented results are preliminary.