Structure of Kepler's SNR and the Crab Nebula at 327 MHz from occultation observations

Abstract

Strip brightness distributions across Kepler's SNR and the Crab Nebula have been obtained at 327 MHz with resolutions of 8 and 26 arcsec respectively from recent occultation observations. A 'plateau' surrounding the strong emission in the shell of Kepler's remnant is observed. The data for both SNRs at 327 MHz have been compared with high-resolution maps at centimetre wavelengths and also with the optical map in the case of the Crab. In the Crab Nebula no appreciable radial variation of the radio spectrum was found, although there is a tendency for it to steepen near the edges. We interpret this steepening in terms of the radiation from the true remnant shell which is masked in the central regions by radiation from pulsar-generated electrons and has therefore been ill-defined hitherto.