GCN Circular 17808

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, hard-spectrum, intense GRB 150510A
(Fermi-LAT detection: Vianello & Racusin, GCN 17805
Not found
 
 
;
Racusin et al., GCN 17806
Not found
 
 
;
Fermi-GBM detection: Burns & Meegan GCN 17807
Not found
 
 
)
triggered Konus-Wind at T0=11988.505 s UT (03:19:48.505).

The KW light curve shows a FRED-like structure with
a duration of ~62 s.
The emission is visible up to ~15 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB150510_T11988/

As observed by Konus-Wind, the burst had a fluence
of 1.9(-0.1,+0.1)x10^-4 erg/cm2, and a 64-ms peak flux,
measured from T0+0.064 s, of 4.0(-0.3,+0.3)x10^-5 erg/cm2/s
(both in the 20 keV - 10 MeV energy range).

The time-averaged spectrum (measured from T0 to T0+39.168 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 = -0.99 (-0.04,+0.05),
the high energy photon index beta = -2.81 (-1.10,+0.37),
the peak energy Ep = 1253 (-129,+134) keV,
chi2 = 106/95 dof.

The spectrum near the peak count rate
(measured from T0 to T0+6.400 s)
is best fit in the 20 keV - 15 MeV range
by the cutoff power law with the following model parameters:
the photon index alpha = -0.74(-0.05,+0.05),
and the peak energy Ep = 1320(-85,+93) keV,
chi2 = 100/87 dof.
Fitting this spectrum with the Band model yields the same
values of alpha and Ep with an upper limit on the high-energy
photon index beta of -2.9

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