TITLE:   GCN CIRCULAR
NUMBER:  29797
SUBJECT: Konus-Wind detection of GRB 210410A
DATE:    21/04/11 18:02:54 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 210410A
(Fermi-GBM detection: Fermi GBM team, GCN 29777,
Wood and Meegan, GCN 29788;
Fermi-LAT detection: Arimoto et al., GCN 29781;
AGILE detection: Ursi et al., GCN 29782;
Swift-BAT observation: Lien et al., GCN 29793)
triggered Konus-Wind at T0=3196.651 s UT (00:53:16.651).

The burst light curve starts at ~T0 with a narrow (~128 ms) pulse
followed by a gradually decaying emission until ~T0+85s.
The emission is seen up to ~10 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB210410_T03196/

As observed by Konus-Wind, the burst
had a fluence of 7.29(-0.44,+0.47)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+0.002 s,
of 2.95(-0.69,+0.76)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+47.104 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.74(-0.07,+0.08)
and Ep = 1081(-126,+150) keV (chi2 = 72/98 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.7
(chi2 = 72/97 dof).

The spectrum of the initial pulse
(measured from T0 to T0+0.128 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model
with  alpha = 0.11(-0.29,+0.38)
and Ep = 1210(-250,+326) keV (chi2 = 38/32 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -1.9
(chi2 = 36/31 dof).

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