Hydrodynamics of Internal Shocks in Relativistic Outflows
  We study the hydrodynamical effects of two colliding shells, adopted to model internal shocks in various relativistic outflows such as gamma-ray bursts and blazars. We find that the density profiles are significantly affected by the propagation of rarefaction waves. A split-feature appears at the contact discontinuity of the two shells. The shell spreading with a few ten percent of the speed of light is also shown to be a notable aspect. The conversion efficiency of the bulk kinetic energy to internal one shows deviations from the widely-used inelastic two-point-mass-collision model. Observational implications are also shortly discussed. 
M. Kino (SISSA), A. Mizuta (Kyoto Univ.), A. Celotti (SISSA), S.   Yamada (Waseda Univ.)