GCN Circular 9196
Subject
GRB 090418A: Konus-Wind and Swift/BAT joint spectral analysis
Date
2009-04-22T20:08:42Z (16 years ago)
From
Valentin Pal'shin at Ioffe Inst <val@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 090418A (Swift/BAT trigger #349510: Mangano et al., GCN Circ.
9149, Fenimore et al. GCN Circ. 9157).
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. 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)-6.7 to T0(BAT)+58.1 sec where T0(BAT) is the trigger time
of BAT at 11:07:40.2 UTC. The energy ranges which we used in the joint
spectral analysis are 20-1200 keV and 14-150 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 is well fitted 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 20%. No systematic residual from the
best fit model is seen in the spectral data of each instrument. The
best fit spectral parameters are: alpha = -1.30 +/- 0.09 and Epeak =
610(-164, +530) keV (chi2/dof = 37.0/57). The best fit spectral
parameters for the GRB (Band) model fixing beta = -2.5 are: alpha = -1.30
+/- 0.09, and Epeak = 601(-215, +554) keV (chi2/dof = 37.1/57). The
energy fluence in the 15-1200 keV band calculated by a power-law with
exponential cutoff model for this 64.8 sec interval is (1.79 +/-
0.21)x10^-5 erg/cm2.
All the quoted errors are at the 90% confidence level.
Assuming z = 1.6 (Chornock et al., GCN Circ. 9151) 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 ~2x10^53 erg in 1 keV to 10
MeV at the GRB rest frame extrapolating the best Band function fit
fixing beta = -2.5.
The Konus-Wind light curve of this GRB is available
at http://www.ioffe.ru/LEA/GRBs/GRB090418A/