TITLE:   GCN CIRCULAR
NUMBER:  40453
SUBJECT: Konus-Wind detection of GRB 250506A
DATE:    25/05/13 10:36:33 GMT
FROM:    Dmitry Svinkin at Ioffe Institute <svinkin@mail.ioffe.ru>

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

The long-duration GRB 250506A
(Fermi-GBM detection: The Fermi GBM team, GCN 40355;
SVOM detection: Wang et al., GCN 40358;
GECAM-B detection: Wang et al., GCN 40396;
GRBAlpha detection: Pal et al., GCN 40440;)
triggered Konus-Wind at T0=08605.817 s UT (02:23:25.817).

The burst light curve shows a multi-peaked structure
which starts at ~T0-2.1 s and has a total duration of ~56 s.
The emission is seen up to ~7 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB250506_T08605

As observed by Konus-Wind, the burst
had a fluence of 2.41(-0.16,+0.38)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+33.728 s,
of 8.39(-0.74,+0.75)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+57.600 s)
is best fit in the 20 keV - 10 MeV range
by the GRB (Band) model with the following parameters:
the low-energy photon index alpha = -1.06(-0.04,+0.08),
the high energy photon index beta = -3.51(-6.49,+0.91),
the peak energy Ep = 284(-28,+28) keV
(chi2 = 123/97 dof).

The spectrum near the maximum count rate
(measured from T0+33.024 to T0+41.216 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 = -1.02(-0.07,+0.08)
and Ep = 278(-21,+25) keV (chi2 = 111/98 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -3.0
(chi2 = 111/97 dof).

All the quoted errors are at the 68% confidence level.
All the quoted values are preliminary.