TITLE:   GCN CIRCULAR
NUMBER:  7630
SUBJECT: GRB 080413A: Suzaku/WAM and Swift/BAT joint spectral analysis
DATE:    08/04/18 21:50:05 GMT
FROM:    Takanori Sakamoto at NASA/GSFC  <takanori.sakamoto-1@nasa.gov>

M. Ohno, M. Kokubun, M. Suzuki, T. Takahashi (ISAS/JAXA)
K. Yamaoka, S. Sugita (Aoyama Gakuin U.),
T. Enoto (Univ. of Tokyo), Y.E. Nakagawa, T. Tamagawa (RIKEN),
T. Uehara, T. Takahashi, Y. Fukazawa, C. Kira, Y. Hanabata
(Hiroshima U.), M. Tashiro,
Y. Terada, Y. Urata, A. Endo, K. Onda, N. Kodaka, K. Morigami (Saitama U.),
K. Nakazawa, K. Makishima (Univ. of Tokyo), E. Sonoda, M. Yamauchi,
H. Tanaka, R. Hara (Univ. of Miyazaki), , S. Hong (Nihon U.),
on behalf of the Suzaku WAM team, report:

J. Tueller (GSFC), 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), T. Sakamoto (GSFC/UMBC),
G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), T. Ukwatta (GWU)
(i.e. the Swift-BAT team):

report:

We performed the Suzaku/WAM and Swift/BAT joint fit spectral
analysis of GRB 080413A (Swift/BAT trigger #309096; Beardmore et al., 
GCN 7594).  The time interval of the spectral data for each 
instrument is chosen from T0(WAM)-1 to T0(WAM)+22 sec where
T0(WAM) is the trigger time of WAM at  02:54:18.648 UTC.  
This time interval includes the initial two peaks, but not 
the relatively soft third peak around T0(WAM)+45 sec which 
is clearly visible in the BAT data (Tueller et al., GCN 7604).  
The energy ranges which we used in the joint spectral analysis
are 13-150 keV and 150-1000 keV for Swift/BAT and Suzaku/WAM
respectively.  The spectral data of two instruments are fit
with the spectral model multiplied by the constant factor to
take into account the systematic 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 20%.  No systematic residual
from the best fit model is seen in the spectral data of each instrument.
The best fit spectral parameters are: alpha = -1.2 +- 0.1 and
Epeak = 170 (-40/+80) keV (chi2/dof = 75/73).  The energy fluence
in the 15-1000 keV band calculated by a power-law with exponential
cutoff model for this 23 sec interval is 4.8 (-1.2/+0.4) x 10^-6 erg/cm2
(assuming the constant factor of the BAT is fixed to 1).

Assuming z = 2.433 (Thoene et al., GCN 7602) 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 ~8x10^52 erg in 1 keV to 10 MeV at the GRB rest frame.   

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