TITLE:   GCN CIRCULAR
NUMBER:  29258
SUBJECT: Konus-Wind detection of GRB 210104A
DATE:    21/01/05 14:17:49 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred@mail.ioffe.ru>

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

The long GRB 210104A (Swift detection:  Troja et al., GCN 29233;
Fermi GBM detection:  Malacaria et al., GCN 29246)
triggered Konus-Wind (KW) at T0=41224.536 s UT (11:27:04.536).

The burst light curve shows multiple partly overlapped peaks
in the interval from ~T0-2 s to ~T0+33 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/GRB210104_T41224/

As observed by Konus-Wind, the burst had
a fluence of (2.15 ± 0.35)x10^-5 erg/cm^2 and
a 64-ms peak energy flux, measured from T0+26.624,
of (1.13 ± 0.19)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).

The time-integrated spectrum (measured from T0 to T0+33.024 s)
is best fit in the 20 keV - 20 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -1.00 (-0.16,+0.18),
the high energy photon index beta = -2.52 (-0.52,+0.24),
the peak energy Ep = 157 (-18,+23) keV,
chi2 = 90/97 dof.

The spectrum near the peak count rate (measured from T0+16.640
to T0+33.024 s) is best fit in the 20 keV - 15 MeV range
by the GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.95 (-0.11,+0.11),
the high energy photon index beta = -2.47 (-1.10,+0.24),
the peak energy Ep = 176 (-24,+37) keV,
chi2 = 83/97 dof.

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