Bulk X-ray Doppler velocities in the supernova remnant Cassiopeia A

We map the average line-of-sight velocities of the X-ray-emitting mass in t he supernova remnant Cassiopeia A using measurements of the centroid of the Si-He alpha blend with the Advanced CCD Imaging Spectrometer on the Chandr a X-Ray Observatory. This 4" scale map confirms the broad trends noted in p revious studies, namely, that the line-of-sight velocity scale is roughly 2 000-3000 km s(-1), with relatively more blueshifted material in the southea stern region of the remnant than in the northwest; new details are that the northwestern region consists of two arcs, with the southernmost one repres enting the most redshifted X-ray-emitting material in Cas A. These results are consistent with contemporaneous results from XMM-Newton. The X-ray patt erns resemble the complex velocity patterns measured at optical wavelengths for much denser ejecta, and they support the growing body of evidence that the explosion and subsequent evolution of Cas A were highly asymmetrical.