Hydrodynamics of Young Supernova Remnants and the Implications for their   Gamma-ray emission
  Supernovae (SNe) are generally classified into Type I and Type II. Most SNe (~ 80%), including all the subtypes of Type II, and Type Ib/c, arise from the core-collapse of massive stars. During their lifetime, mass-loss from these stars considerably modifies the medium around the stars. When the stars explode as SNe, the resulting shock wave will expand in this wind-modified medium. In contrast, Type Ia SNe will expand in a relatively uniform medium, but the dynamics are different from those of core-collapse SNe. For young supernova remnants, the properties of the ejecta as well as the surrounding medium are important in determining the subsequent evolution of the SN shock wave, and the dynamics and kinematics of the remnant. This will influence the acceleration of particles at the SN shocks, and consequently affect the gamma-ray emission from the remnant.   Herein we discuss the expected properties, especially the density structure, of the medium around various types and sub-types of SNe, as suggested by current stellar evolution models. Using analytic and semi-analytic models and numerical simulations, we investigate how these affect the kinematics of the SN shock waves, assess the impact this would have on the production of cosmic rays, and show how it influences the time-evolution of the hadronic gamma-ray emission from the remnant. In the case of SNRs evolving in a wind medium, the emission should reach a maximum early on, and thereafter decrease with time. For SNe in a constant density medium, the emission would be expected to increase with time upto the advent of the Sedov stage. 
Vikram Dwarkadas (University of Chicago)
astro-ph.HE