One of the challenges of the Swift era has been accurately determining Epeak
for the prompt GRB emission. RHESSI, which is sensitive from 30 keV to 17 MeV,
can extend spectral coverage above the Swift-BAT bandpass. Using the public
Swift data, we present results of joint spectral fits for 26 bursts co-observed
by RHESSI and Swift-BAT through May 2007. We compare these fits to estimates of
Epeak which rely on BAT data alone. A Bayesian Epeak estimator gives better
correspondence with our measured results than an estimator relying on
correlations with the Swift power law indices.Comment: 4 pages, 1 figure. To appear in the proceedings of Gamma Ray Bursts
2007, Santa Fe, New Mexico, November 5-9 200
