GCN Circular 9821

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
Not found
 
 
, Baumgartner et al. GCN Circ. 
9775
Not found
 
 
) 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
Not found
 
 
) 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/