[vsnet-grb-info 7878] GRB 090516A: Konus-Wind and Swift/BAT joint spectral analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9422
SUBJECT: GRB 090516A: Konus-Wind and Swift/BAT joint spectral analysis
DATE:    09/05/24 17:27:29 GMT
FROM:    Takanori Sakamoto at NASA/GSFC  <takanori.sakamoto-1 at nasa.gov>

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)

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

We performed the Konus-Wind and the Swift/BAT joint spectral analysis
of GRB 090516A (Swift/BAT trigger #352190: Rowlinson et al., GCN Circ. 
9374, Baumgartner et al. GCN Circ. 9384).  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.  The 
joint spectral analysis of the Konus-Wind and the Swift/BAT data 
allows us 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)-12.2 to T0(BAT)+96.7 sec where T0(BAT) is the trigger time
of BAT at 08:27:50.8 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 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 = -1.5 (-0.3/+0.2) and Epeak 
= 190 (-65/+230) keV (chi2/dof = 54/56).  The best fit spectral 
parameters for the GRB (Band) model fixing beta = -2.5 are: 
alpha = -1.5 (-0.2/+0.3), and Epeak = 190 (-75/+270) keV (chi2/dof = 55/56).
The energy fluence in the 15-1200 keV band calculated by a power-law 
with exponential cutoff model for this 107.9 sec interval is 
(1.5 +/- 0.3)x10^-5 erg/cm2.

Assuming z = 4.109 (de Ugarte Postigo et al. GCN Circ. 9383) 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 = 6.5 (-1.1/+1.4) x10^53 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/GRB090516/ 

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