RXTE OBSERVATIONS OF CAS-A

Rossi X-ray Timing Explorer (RXTE) observations of the bright supernov a remnant Cas A have revealed a hard power law component above 10 keV in addition to two thermal components inferred from ASCA measurements of the many line centroids from low-Z elements. The power law can be s hown to be consistent with synchrotron emission from radio to hard x-r ays by electrons of up to 4x10(13) eV. Measurement of the 1157 keV lin e by CGRO from Sc-44 in the chain of decay of Ti-44 predicts that the two Ti-44 lines at 68 and 78 keV should appear at the CGRO intensity. RXTE has placed upper limits on such lines that are marginally consist ent with the CGRO measurement. Implications of these results on sites for cosmic ray acceleration and nucleosynthesis are discussed.