X-ray synchrotron in the forward shock of Cassiopeia A

We present high spatial resolution spectra of the forward shock of Cassiopeia A from a 50 ks observation obtained by the Advanced CCD Imaging Spectrometer on board the Chandra X-ray Observatory. We systematically compare the spectra of several regions of the forward shock and find that single-component non-equilibrium ionization models do not provide good fits to the spectra. Our preliminary results indicate that it is necessary to add a nonthermal, synchrotron component that dominates the continuum uf the spectrum above 3 keV. We find that the shape of this nonthermal continuum changes from region to region which may indicate variable acceleration conditions within the remnant.