TITLE:   GCN CIRCULAR
NUMBER:  35864
SUBJECT: Konus-Wind detection of GRB 240303B
DATE:    24/03/04 18:41:13 GMT
FROM:    Dmitry Frederiks at Ioffe Institute <fred@mail.ioffe.ru>

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

The long GRB 240303B (Fermi GBM detection:
Fermi GBM team, GCN 35850; Hamburg and Meegan, GCN 35860;
CALET detection: Nakahira et al., GCN 35857;
IPN localization: Kozyrev et al., GCN 35862)
triggered Konus-Wind (KW) at T0=44327.406 s UT (12:18:47.406).

The burst light curve shows a bright initial pulse,
which starts at ~T0-0.5s, peaks at ~T0+4s, and has a duration of ~6.5s.
This pulse is followed by a weaker extended emission that lasts
up to ~T0+250s.
The emission in is seen up to ~3 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB240303_T44327/

As observed by Konus-Wind, the initial pulse had
a fluence of (2.62 ± 0.27)x10^-5 erg/cm^2 and
a 64-ms peak energy flux, measured from T0+4.032 s,
of (1.11 ± 0.12)x10^-5 erg/cm^2/s (both in the 20 keV - 10 MeV energy range).

A time-averaged spectrum of this pulse (measured from T0 to T0+6.4 s)
is best fit in the 20 keV - 15 MeV range
by a GRB (Band) function with the following model parameters:
the low-energy photon index alpha = -0.21 (-0.12,+0.12),
the high energy photon index beta = -2.69 (-0.77,+0.27),
the peak energy Ep = 422 (-49,+61) keV,
chi2 = 92/77 dof.

A spectrum of the extended emission (measured from T0+30.976 to T0+252.16 s)
is best fit by a simple power-law (PL) function with
the PL index of -1.42(-0.22,+0.18), chi2 = 86/99 dof.
A 20-3000 keV fluence in this interval is estimated to (2.42 ± 0.63)x10^-5 erg/cm^2.


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