Two-fluid blast-wave model for supernova remnants

The structure and X-ray emission of supernova remnants (SNRs) in the adiabatic phase of evolution may depend critically on whether or not electron and ion temperatures are equilibrated at the strong collisionless shock front. We focus upon the case that the electrons are not heated significantly at the shock front. Ignoring thermal conduction, we obtain an approximate analytic solution to an energy equation for the shocked electron gas. This solution shows that Coulomb interactions are insufficient to equilibrate electron and ion temperatures within SNRs younger than -- 104 yr. In the two-fluid phase, the characteristic X-ray temperature of the remnant (-- 107K) is much lower than that predicted by one-fluid models, and is insensitive to the remnant's age. A method of estimating SNR parameters from X-ray observations is described and applied to real objects. IC443 is predicted to be in the two-fluid phase, while departure from temperature equilibrium is indicated to be small in the Cygnus Loop, Vela, MSH 14-63, and Puppis A. The remnant of SN 1006 and SNR G 287.8-0.5 are suggested to be in the early phase of evolution. (author)