We present our broadband spectral investigations of 42 SGR J1550-5418 bursts simultaneously detected with the Fermi/Gamma-ray Burst Monitor (GBM) and the Swift X-ray Telescope (XRT), during the 2009 January active episode of the source. The unique spectral and temporal capabilities of GBM and XRT have allowed us to study the burst spectra in a very wide energy band (0.5-200 keV). We find that, on average, SGR burst spectra are better described with two blackbody functions than with the Comptonized model. Thus, our joint XRT-GBM analysis clearly shows for the first time that the SGRJ1550- 5418 burst spectra might naturally be expected to exhibit a more truly thermalized character, such as a two-blackbody or even a multi-blackbody signal.
Our joint spectral fits also provide an opportunity to investigate the cross-calibration of the XRT and GBM instruments with the two spectral models. Finally, we show that the distribution of the XRT burst counts with spin phase is not uniform and not correlated with the persistent X-ray emission pulse phase of SGRJ1550-5418. This indicates that the surface magnetic field of SGRJ1550-5418 is not uniform over the emission zone and the burst emitting sites on the neutron star need not to be co-located with hot spots emitting the bulk of the persistent X-ray emission.