GCN Circular 5477

T. Sakamoto (GSFC/ORAU), G. Sato (GSFC/ISAS), S. D. Barthelmy (GSFC), 
J. Cummings (GSFC/ORAU), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), 
A. Parsons (GSFC), J. Tueller (GSFC), L. Barbier (GSFC), 
E. Fenimore (LANL), D. Hullinger (BYU-Idaho), M. Koss (GSFC/UMD), 
C. Markwardt (GSFC/UMD), D. Palmer (LANL), M. Stamatikos (GSFC/ORAU), 
on behalf of the Swift-BAT team, 

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

M. Ohno, T. Takahashi, T. Asano, T. Uehara, Y. Fukazawa (Hiroshima U.),
K. Yamaoka, S. Sugita (Aoyama Gakuin U.), 
Y. Terada, T. Tamagawa, M. Suzuki (RIKEN), 
K. Abe, K. Onda, Y. Urata, M. Suzuki, M. Tashiro (Saitama U.),
S. Hong (Nihon U.), K. Nakazawa, T. Takahashi (ISAS/JAXA), 
T. Enoto, R. Miyawaki, K. Kokubun, K. Makishima (Univ. of Tokyo)
on behalf of the Suzaku-WAM team, 

report:

We performed the Swift/BAT, Konus-Wind, and Suzaku/WAM joint fit spectral 
analysis of GRB 060813 (Swift-BAT trigger #224364; Moretti, et al., 
GCN Circ. 5442
Not found
 
 
).  The time interval of the spectral data for each instrument 
is chosen as the same interval as the Konus-Wind time-averaged spectrum 
reported by Golenetskii et al. (GCN Circ. 5446
Not found
 
 
).  The energy ranges which we 
used in the joint spectral analysis are 14-150 keV, 20-1000 keV, 
and 100-1000 keV, for Swift/BAT, Konus-Wind and Suzaku/WAM respectively.  
The spectral data of three instruments are fitted with the spectral model 
multiplied by the constant factor to take into account the systematic 
uncertainties in the response matrices of each instrument.  

The spectrum is well fitted with a power-law time exponential cutoff model 
(dN/dE ~ E^{alpha} * exp(-(2+alpha)*E/Epeak)).  The constant factors of each 
instrument agree within 10%.  No systematic residual from the best fit model 
is seen in the spectral data of each instrument.  The best fit spectral 
parameters are: alpha = -0.83 +- 0.05 and Epeak = 240 (-10/+11) keV 
(chi2/dof = 135/125).  Although there is no significant improvement in the 
fit, the best fit parameters in the Band function are: the low-energy 
photon index alpha = -0.79 +- 0.06, the high energy photon index 
beta = -2.71 (-0.70/+0.24) and Epeak = 230 (-14/+15) keV 
(chi2/dof = 133/124).  The energy fluence in the 15-1000 keV band calculated 
by the Band function is 1.22 +- 0.05 x 10^-5 erg/cm2 (in case the constant 
factor of the Konus-Wind is fixed to 1).  The spectral paramters in a 
power-law time exponential cutoff model for Swift/BAT and Suzaku/WAM were 
reported by Cummings et al. (GCN Circ. 5443
Not found
 
 
) and by Yamaoka, et al. 
(GCN Circ. 5462
Not found
 
 
).  The Konus-Wind best fit spectral parameters for a 
power-law time exponential cutoff model are:  alpha = -0.65 (-0.12, +0.11), 
Epeak = 214 (-15, +17) keV (chi2/dof = 81/59).  Our joint fit spectral 
parameters in a power-law time exponential cutoff model are consistent 
within 90% confidence level with the spectral parameters derived by individual 
instruments.  However, we do see a systematic difference in the spectral 
parameters in the Band function fit especially in the low energy photon 
index alpha.  We are still working on the cross-calibration among three 
instruments.  

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

[GCN OPS NOTE(25aug06): Per author's request, the last two words were added
to the Subject line.]