TITLE:   GCN CIRCULAR
NUMBER:  13614
SUBJECT: GRB 120804A: Konus-Wind and Swift/BAT joint spectral analysis
DATE:    12/08/09 19:48:56 GMT
FROM:    Valentin Pal'shin at Ioffe Inst  <val@mail.ioffe.ru>

T. Sakamoto (GSFC/UMBC), S. D. Barthelmy (GSFC),
W. Baumgartner (GSFC/UMBC), J. Cummings (GSFC/UMBC),
E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA),
C. Markwardt (GSFC/UMD), D. Palmer (LANL), G. Sato (ISAS),
M. Stamatikos (OSU), J. Tueller (GSFC), and T. Ukwatta (MSU)
on behalf of the Swift-BAT team,

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

The short GRB 120804A (Swift/BAT trigger #529686: Lien et al., GCN Circ.
13573, Baumgartner et al. GCN Circ. 13581) triggered Konus-Wind at
T0=3255.749 s UT (00:54:15.749), but since the incident angle on the
triggered detector was 99.2 deg (i.e. the burst accidentally triggered
the S2 detector which observes the northern ecliptic hemisphere,
although the burst came from the southern ecliptic hemisphere: b = -9.2
deg) the standard analysis of the Konus-Wind spectral data is impossible.

To derive the broad-band spectral parameters of this burst, we performed
joint spectral analysis of the Swift/BAT data and the Konus-Wind
3-channel spectral data (obtained in the waiting mode from the detector
S1), which covers the energy range from 24 keV to 1.4 MeV.

The time intervals of the spectral data are chosen for the Konus-Wind
from T0(BAT)-0.916 s to T0(BAT)+2.028 s (single KW bin which comprises
the burst) and for the Swift/BAT from T0(BAT)-0.16 s to T0(BAT)+0.83 s
(that is the BAT T100 interval), where T0(BAT) is the trigger time of
BAT at 00:54:14.18 UTC. The energy ranges which we used in the joint
spectral analysis are 24-1400 keV and 14-150 keV for the Konus-Wind and
the Swift/BAT respectively.  The spectral data of the two instruments 
are fitted with the spectral model multiplied by a constant factor to 
take into account the systematic effective area uncertainties in the 
response matrices of each instrument and the difference in the chosen 
intervals.

The spectrum is well fitted with a power-law with exponential cutoff
model: dN/dE ~ E^{alpha}*exp(-(2+alpha)*E/Epeak). 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 (-0.28, +0.24) and
Epeak = 135 (-29, +66) keV (chi2/dof = 56/58).

The energy fluence and 16-ms peak flux in the 15-1000 keV band
are 1.45 (-0.31,+0.30) x 10^-6 erg/cm2 and (6.0 ± 2.7) x 10^-6 erg/cm2/s 
respectively.

The Konus-Wind light curve of this GRB is available at
http://www.ioffe.ru/LEA/GRBs/GRB120804_T03255/

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