EXOSAT spectral observations of Crab-like SNR's.

Broad-band X-ray (2 - 10 keV) spectral data are presented on the Crab-like supernova remnants G21.5-0.9, 3C58 and Vela, as obtained from the medium energy instrument onboard EXOSAT. The authors find all these objects to show power law spectra, with a range of energy index between 0.5 and 1.5. The measured column density for G21.5-0.9 is consistent with a distance of ≡5 kpc. The overall electromagnetic spectra lead to interpolated break frequencies from 10¹⁰ - 10¹⁴Hz and a wide range of X-ray to radio luminosities. These properties are compared to the Crab Nebula, as the class progenitor, and to current model predictions.