TITLE: GCN CIRCULAR NUMBER: 9821 SUBJECT: GRB 090812: Konus-Wind and Swift/BAT joint spectral analysis DATE: 09/08/17 15:28:46 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), D. Palmer (LANL), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), and T. Ukwatta (GWU) report: The most intense pulse of the long GRB 090812 (Swift/BAT trigger #359711: Stamatikos et al., GCN Circ. 9768, Baumgartner et al. GCN Circ. 9775) triggered Konus-Wind at T0(KW)=21758.942 s UT (06:02:38.942). Since the Konus-Wind trigger record misses the early weaker part of this GRB, we have only Konus-Wind 3-channel spectral data for the whole burst which cover the energy range from 23 keV to 1.4 MeV. We performed the Konus-Wind and Swift/BAT joint spectral analysis of this GRB to derive the broad-band spectral and energetic parameters of this burst. The time interval of the spectral data is chosen from T0(BAT)-6.7 to T0(BAT)+58.1 sec where T0(BAT) is the trigger time of BAT at 06:02:08.897 UTC. The energy ranges which we used in the joint spectral analysis are 23-1400 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 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 15%. No systematic residual from the best fit model is seen in the spectral data of each instrument. The best fit spectral parameters are: alpha = -1.03(-0.06, +0.07) and Epeak = 586(-152, +243) keV (chi2/dof = 59.3/57). The best fit spectral parameters for the GRB (Band) model fixing beta = -2.5 are: alpha = -1.03 +/- 0.07, and Epeak = 572(-159, +251) keV (chi2/dof = 59.6/57). The energy fluence in the 15-1400 keV band calculated by a power-law with exponential cutoff model for this 64.8 sec interval is (2.61 +/- 0.34)x10^-5 erg/cm2 (assuming the constant factor of the Konus-Wind is fixed to 1). Assuming z = 2.452 (de Ugarte Postigo et al. GCN Circ. 9771) 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 = 4.4 (-0.6, +0.7)x10^53 erg in 1 keV to 10 MeV at the GRB rest frame extrapolating the best Band function fit fixing beta = -2.5, and the rest frame peak energy is Epeak_rest = 2.0(-0.5, +0.9) MeV. 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/GRB090812_T21758/