An explanation of the formation of the peculiar periphery of Tycho's supernova remnant

Tycho's supernova remnant (SNR) has a periphery which clearly deviates from spherical shape bash on the X-ray and radio observations. The forward shock from the southeast to the north of the remnant has a relatively deformed outline with a depression in the east, although in the west it is generally round and smooth. Moreover, at some locations of the shell, the supernova ejecta distributes closely to the forward shock to produce protrusions. Using 3D hydrodynamical simulation, the dynamical evolution of the supernova ejecta in an inhomogeneous medium and the formation process of the profile of the forward shock can be studied. To reproduce the peculiar periphery of the remnant, we propose a model in which the supernova ejecta has evolved in a cavity blown by a latitude-dependent outflow. The results indicate that, with the assumptions of the wind bubble driven by the anisotropic wind with a mass loss rate of $\sim10^{-7} {\rm M_{\odot}}$~yr$^{-1}$, a pole velocity of $\sim 100$~km s$^{-1}$, a duration of $\sim10^5$~yr just before the supernova explosion, and a spatial velocity of $\sim 30$~km s$^{-1}$ of the progenitor with respect to the circumstellar medium, the depression to the east and the protrusion to the southeast on the observed periphery of the remnant can be generally reproduced. In conclusion, an explanation to the peculiar shape of the periphery of Tycho's SNR is the supernova ejecta evolved in the cavity driven by the latitude-dependent wind.