TITLE:   GCN CIRCULAR
NUMBER:  30007
SUBJECT: Konus-Wind detection of GRB 210511B
DATE:    21/05/13 20:48:20 GMT
FROM:    Anna Ridnaia at Ioffe Institute  <ridnaia@mail.ioffe.ru>

A. Ridnaia, D. Frederiks, S. Golenetskii, A. Lysenko, D. Svinkin,
A. Tsvetkova,  M. Ulanov, and T. Cline, report:

The long-duration GRB 210511B
(Fermi GBM detection: Fermi GBM team, GCN 29988;
Bissaldi and Meegan, GCN 29996;
BALROG localization: Kunzweiler et al., GCN 29989;
GECAM detection: Cai et al., GCN 29990;
AGILE detection: Ursi et al., GCN 29991;
IPN triangulation: Hurley et al., GCN 30002)
triggered Konus-Wind at T0=41201.35 s UT (11:26:41.350).

The burst light curve shows a multi-peaked structure
which starts at ~T0-1.7 s and has a total duration of ~6 s.
The emission is seen up to ~4 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB210511_T41201/

As observed by Konus-Wind, the burst
had a fluence of 1.10(-0.15,+0.18)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+0.512 s,
of 4.76(-1.24,+1.34)x10^-6 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum of the burst
(measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 4 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -0.98(-0.15,+0.18),
the high energy photon index beta = -2.48(-0.43,+0.23),
the peak energy Ep = 154(-22,+25) keV
(chi2 = 86/71 dof).

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