EVIDENCE FOR THERMAL ABSORPTION INSIDE CASSIOPEIA-A

Subarcminute resolution images of Cas A at 74 and 333 MHz are presente d, Comparison with each other and with higher frequency observations i ndicates that the spectral index of its nonthermal emission flattens b elow 333 MHz and that the effect is confined toward the central 1' of the source and is maximum at its center. The source of the flattening is unknown, although we show that the data are consistent with absorpt ion by ionized gas inside the radio shell. Such a component may be rel ated to unshocked ejecta still freely expanding within the boundaries of the reverse shock as delineated by X-ray observations.