X-RAY AND GAMMA-RAY EMISSION FROM MIDDLE-AGED SUPERNOVA REMNANTS IN CAVITIES. I. SPHERICAL SYMMETRY

We present analytical and numerical studies of models of supernova-remnant (SNR) blast waves in one spatial dimension expanding into uniform media and interacting with a denser cavity wall. We predict the nonthermal emission from such blast waves: synchrotron emission at radio and X-ray energies, and bremsstrahlung, inverse-Compton emission (from cosmic-microwave-background seed photons; ICCMB), and emission from the decay of pi(0) mesons produced in inelastic collisions between accelerated ions and thermal gas, at GeV and TeV energies. Accelerated-particle spectra are assumed to be power laws with exponential cutoffs at energies limited by the remnant age or (for electrons, if lower) by radiative losses. We compare the results with those from homogeneous ("one-zone") models. Such models give fair representations of the 1D results for uniform media, but cavity-wall interactions produce effects for which one-zone models are inadequate. We study the time evolution of SNR morphology and emission with time. Strong morphological differences exist between ICCMB and pi(0)-decay emission; at some stages, the TeV emission can be dominated by the former and the GeV by the latter, resulting in strong energy. dependence of morphology. Integrated gamma-ray spectra show apparent power laws of slopes that vary with time, but do not indicate the energy distribution of a single population of particles. As observational capabilities at GeV and TeV energies improve, spatial inhomogeneity in SNRs will need to be accounted for.