GCN Circular 18516

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

The long-duration GRB 151027A
(Swift-BAT trigger #661775: Maselli et al., GCN Circ. 18478
Not found
 
 
,
Palmer et al., GCN Circ. 18496
Not found
 
 
;
Fermi GBM detection: Toelge et al., GCN Circ. 18492
Not found
 
 
)
triggered Konus-Wind at T0=14304.154 s UT (03:58:24.154).

The burst light curve consists of at least three pulses
with a total duration of ~120 s.
The emission is seen up to ~5 MeV.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB151027_T14304/

As observed by Konus-Wind, the burst
had a fluence of 1.42(-0.21,+0.37)x10^-5 erg/cm2,
and a 64-ms peak flux, measured from T0+0.432 s,
of 2.22(-0.61,+0.62)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+131.328 s)
is best fit in the 20 keV - 5 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -1.44(-0.21,+0.24)
and Ep = 173(-46,+135) keV (chi2 = 78/77 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.0
(chi2 = 77/76 dof)

The spectrum near the maximum count rate
(measured from T0 to T0+8.448 s)
is best fit in the 20 keV - 2 MeV range
by a power law with exponential cutoff model:
dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep)
with  alpha = -0.96(-0.28,+0.32)
and Ep = 91(-11,+14) keV (chi2 = 56/61 dof).
Fitting by a GRB (Band) model yields the same alpha and Ep,
and an upper limit on the high energy photon index: beta < -2.7
(chi2 = 56/60 dof)

Assuming the redshift z=0.81 (Perley et al., GCN Circ. 18487
Not found
 
 
)
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 ~2.4x10^52 erg,
the peak luminosity L_iso is ~7x10^51 erg/s,
and the rest-frame peak energy of the time-integrated spectrum,
Ep,i, is ~310 keV.

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