TITLE:   GCN CIRCULAR
NUMBER:  17677
SUBJECT: Konus-Wind observation of GRB 150403A
DATE:    15/04/05 12:02:58 GMT
FROM:    Dmitry Frederiks at Ioffe Institute  <fred@mail.ioffe.ru>

S. Golenetskii, R.Aptekar, D. Frederiks, V. Pal'shin, P. Oleynik,
M. Ulanov, D. Svinkin, A. Tsvetkova, A.Lysenko, and T. Cline
on behalf of the Konus-Wind team, report:

The long-duration, intense GRB 150403A
(Swift-BAT trigger #637044: Lien et al., GCN 17665;
Sakamoto et al., GCN 17675;
Fermi-LAT detection: Longo et al., GCN 17667;
Fermi-GBM detection: Zhang, GCN 17674)
triggered Konus-Wind at T0=78852.693 s UT (21:54:12.693).

The KW light curve shows a single bright pulse with a duration of ~26 s.
The emission is visible up to ~10 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB150403_T78852/

As observed by Konus-Wind, the burst had a fluence
of 1.0(-0.1,+0.1)x10^-4 erg/cm2, and a 64-ms peak flux,
measured from T0+9.088 s, of 1.7(-0.1,+0.1)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum (measured from T0 to T0+27.136 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 = -0.93 (-0.07,+0.08),
the high energy photon index beta = -2.06 (-0.12,+0.08),
the peak energy Ep = 373 (-48,+58) keV,
chi2 = 124/97 dof.

The spectrum near the peak count rate
(measured from T0+7.168 to T0+10.752 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 = -0.78 (-0.08,+0.10),
the high energy photon index beta = -2.13 (-0.12,+0.09),
the peak energy Ep = 430 (-57,+64) keV,
chi2 = 117/97 dof.

Assuming the redshift z=2.06 (Pugliese et al., GCN 17672)
and a standard cosmology model with H_0 = 70 km/s/Mpc,
Omega_M = 0.27, and Omega_Lambda = 0.73,
we estimate the following rest-frame parameters:
the isotropic energy release E_iso is ~1.0x10^54 erg,
the peak luminosity L_iso is ~5.3x10^53 erg/s,
and the rest-frame peak energy of the time-integrated spectrum,
Ep,i, is ~1320 keV.


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