Jets as diagnostics of the circumstellar medium and the explosion energetics of Supernovae: the case of Cassiopeia A

We present hydrodynamical models for the Cassiopeia A (Cas A) supernova remnant and its observed jet/counterjet system. We include the evolution of the progenitor's circumstellar medium, which is shaped by a slow red supergiant wind that is followed by a fast Wolf-Rayet (WR) wind. The main parameters of the simulations are the duration of the WR phase and the jet energy. We find that the jet is destroyed if the WR phase is sufficiently long and a massive circumstellar shell has formed. We therefore conclude that the WR phase must have been short (a few thousand years), if present at all. Since the actual jet length of Cas A is not known, we derive a lower limit for the jet energy, which is ~1048 erg. We discuss the implications for the progenitor of Cas A and the nature of its explosion.