GCN Circular 17731

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, and

T. Sakamoto (AGU), S. D. Barthelmy (GSFC), W. Baumgartner (GSFC/UMBC),
J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC), D. Palmer (LANL), M.
Stamatikos (OSU) and T. Ukwatta (GWU), report:

We performed the Konus-Wind and the Swift/BAT joint spectral analysis of
GRB 150413A
(Swift/BAT trigger #637899: Markwardt et al., GCN Circ. 17688
Not found
 
 
; Stamatikos
et al., GCN Circ. 17701
Not found
 
 
).
Since the Konus-Wind observed this GRB in the waiting mode, we only have 3
channel spectral data for
the Konus-Wind which cover the energy range from 20 keV to 1.2 MeV.

The joint spectral analysis of the Konus-Wind and the Swift/BAT data
allows us
to derive the broad-band spectral parameters of this burst.

The time intervals of the spectral data for each instrument are chosen
from T0(BAT)-102.150 s to T0(BAT)+159.866 s (the time-integrated spectrum)
and from T0(BAT)+95.098 s to T0(BAT)+118.650 s (the spectrum of the most
prominent pulse)
where T0(BAT) is the trigger time of BAT at 13:54:58 UTC.

The energy ranges which we used in the joint spectral analysis are 20-1200
keV and 15-150 keV
for the Konus-Wind and the Swift/BAT respectively.  The spectral data of
two instruments
are fitted with the spectral model multiplied by the constant factor to
take into account
the systematic effective area uncertainties in the response matrices of
each instrument.

The spectrum of the most prominent pulse is well fitted with
a power-law with exponential cutoff model: dN/dE ~
E^{alpha}*exp(-(2+alpha)*E/Epeak).
No systematic residual from the best fit model is seen in the spectral
data of each instrument.

The BAT constant factor is  0.71(-0.12,+0.16) (the KW constant factor is
fixed to 1).
The best fit spectral parameters are:
alpha = -1.01(-0.44,+0.65), and
Epeak = 96(-22,+56) keV (chi2/dof = 60/57).

The best fit spectral parameters for the GRB (Band) model fixing beta =
-2.5 are:
alpha =  -1.00(-0.51,+0.84), and
Epeak = 91(-26,+77) keV
(chi2/dof = 63/57).

The time-integrated spectrum is well fitted with a power-law model
with the the photon index 1.77(-0.09,+0.09), chi2/dof = 68/58.
The BAT constant factor is  0.70(-0.09,+0.11) (the KW constant factor is
fixed to 1).
The energy fluence in the 15-1200 keV band calculated by a power-law model
for this 262.016 s interval is 1.42(-0.19,+0.20)x10^-5 erg/cm2.

Assuming a redshift of 3.139 (de Ugarte Postigo and Tomasella, GCN Circ.
17710
Not found
 
 
)
and a standard cosmology model with H_0 = 67.3 km/s/Mpc, Omega_M = 0.315,
Omega_Lambda = 0.685,
the isotropic energy release in the 1 keV - 10 MeV energy range is
E_iso = 6.53(-1.29,+1.62)x10^53 erg.

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

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB150413A/