TITLE:   GCN CIRCULAR
NUMBER:  42297
SUBJECT: Konus-Wind detection of GRB 251007A
DATE:    25/10/15 17:55:01 GMT
FROM:    Anna Ridnaia at Ioffe Institute <ridnaia@mail.ioffe.ru>

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

The long-duration GRB 251007A
(Swift-BAT detection: Ambrosi et al., GCN 42146;
Laha et al., GCN 42186;
Glowbug detection: Cheung et al., GCN 42151;
CALET-GBM detection: Yoshida et al., GCN 42156;
AstroSat CZTI detection: Salunke et al., GCN 42167;
Insight-HXMT detection: Wang et al., GCN 42183;
SVOM/GRM detection: Yu et al., GCN 42184)
triggered Konus-Wind at T0=70671.956 s UT (19:37:51.956).

The burst light curve shows a multipeaked structure
which starts at ~T0-44.6 s and has a total duration of ~66.4 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/GRB251007_T70671/

As observed by Konus-Wind, the burst
had a fluence of 3.89(-0.15,+0.16)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+0.656 s,
of 7.08(-0.94,+0.95)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+24.832 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 = -1.09(-0.06,+0.06)
and Ep = 395(-27,+31) keV (chi2 = 108/98 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.6
(chi2 = 108/97 dof).

The spectrum near the maximum count rate
(measured from T0+0.256 to T0+8.448 s)
is best fit in the 20 keV - 10 MeV range
by a power law with exponential cutoff model
with  alpha = -1.20(-0.07,+0.07)
and Ep = 436(-41,+50) keV (chi2 = 98/81 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.4
(chi2 = 96/80 dof).

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