[vsnet-grb-info 6652] GRB 080913: Konus-Wind and Swift/BAT joint spectral analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8256
SUBJECT: GRB 080913: Konus-Wind and Swift/BAT joint spectral analysis
DATE:    08/09/17 09:41:53 GMT
FROM:    Valentin Pal'shin at Ioffe Inst  <val at mail.ioffe.ru>

V. Pal'shin, S. Golenetskii, R.Aptekar, E. Mazets, D. Frederiks, and
T. Cline on behalf of the Konus-Wind team,

T. Sakamoto (GSFC/UMBC), S. D. Barthelmy (GSFC),
W. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), K. McLean (GSFC/UMD),
D. Palmer (LANL), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU),
J. Tueller (GSFC), and T. Ukwatta (GWU)
on behalf of the Swift-BAT team,

report:

We performed the Konus-Wind and the Swift/BAT joint spectral analysis
of GRB 080913 (Swift/BAT trigger #324561: Schady et al., GCN Circ. 8217,
Stamatikos et al. GCN Circ. 8222).
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 1.3 MeV.  Therefore, the joint spectral analysis of
the Konus-Wind and the Swift/BAT data enables to derive the broad-band
spectral parameters of this burst.

The time interval of the spectral data for each instrument is chosen
from  T0(BAT)-4.1 to T0(BAT)+4.7 sec where T0(BAT) is the trigger time
of BAT at 06:46:54.1 UTC.  The energy ranges which we used in the joint
spectral analysis are 20-1300 keV and 14-150 keV for the Konus-Wind and
the Swift/BAT respectively.  The spectral data of two instruments are
fit 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 is well fit with a power-law with exponential cutoff model:
dN/dE ~ E^{alpha}*exp(-(2+alpha)*E/Epeak). The constant factors of each
instrument agree within 5%.  No systematic residual from the best fit
model is seen in the spectral data of each instrument.  The best fit
spectral parameters are: alpha = -0.89(-0.46, +0.65) and Epeak = 131
(-48/+225) keV (chi2/dof = 43.7/58).  The best fit spectral parameters
for the Band function fixing beta=-2.5 are: alpha = -0.82(-0.53, +0.75)
and Epeak = 121 (-39/+232) keV (chi2/dof = 43.9/58).  The energy fluence
in the 15-1000 keV band calculated by a power-law with exponential
cutoff model for this 8.8 sec interval is 8.5(-2.2, +6.0)x10^-7 erg/cm2

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

Assuming z = 6.7 (Fynbo et al., GCN Circ. 8225) and a standard cosmology
model with H_0 = 71 km/s/Mpc, Omega_M = 0.27, Omega_Lambda = 0.73, the
isotropic energy  release is E_iso ~7x10^52 erg in 1 keV to 10 MeV at
the GRB rest frame extrapolating the best Band function fit fixing
beta=-2.5.

Looking only at the parameters of the prompt emission, namely T90~1 sec
and Ep ~900 keV in the GRB rest frame, this burst could be classified as
a short burst.