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 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.