The early evolution of supernova remnants in a homogeneous medium - The effects of electron thermal conduction

Abstract

The role of electron thermal conduction in the evolution of supernova remnants may be fully understood only in the context of a two-fluid model, in which electron and ion temperatures are distinguished. During the early stages of supernova remnant evolution, high electron temperatures within the remnant imply that time scales for energy exchange by Coulomb collisions are long. Within the blast wave shock, electron and ion temperatures may be equalized by plasma instabilities, but in the interior of the remnant they may differ substantially. Only electron temperature profiles are fully smoothed by thermal conduction; ion temperatures in the interior of the remnant may remain high.Electron thermal conduction through the blast wave shock itself may be suppressed by magnetic field effects and by plasma instabilities. We suggest that this is required if the remnant is to maintain approximate spherical symmetry while expanding in an ordered magnetic field.We present two-fluid numerical simulations of remnant evolution in a homogeneous medium which illustrate the importance of these effects. Density profiles within the remnant are intermediate in form between those of nonconductive one-fluid simulations and those obtained in the isothermal blast wave similarity solution of Solinger et al. The radius of the remnant differs frommore » that of the Sedov solution by less than a factor of 1.08. We briefly discuss the applicability of theory to observed remnants and discuss some possible tests. We emphasize that the discovery of iron emission lines in young remnants does not necessarily imply that the spectra should be interpreted as bremsstrahlung from a Maxwellianized electron distribution, but may be due instead to a suprathermal electron population.« less