  The explosion mechanism of core-collapse supernovae has not been fully
understood yet but multi-dimensional fluid instabilities such as standing
accretion shock instability (SASI) and convection are now believed to be
crucial for shock revival. Another multi-dimensional effect that has been
recently argued is the asymmetric structures in progenitors, which are induced
by violent convections in silicon/oxygen layers that occur before the onset of
collapse, as revealed by recent numerical simulations of the last stage of
massive star evolutions. Furthermore, it has been also demonstrated numerically
that accretions of such non-spherical envelopes could facilitate shock revival.
These two multi-dimensional may hence hold a key to successful explosions. In
this paper, we performed a linear stability analysis of the standing accretion
shock in core-collapse supernovae, taking into account non-spherical, unsteady
accretion flows onto the shock to clarify the possible links between the two
effects. We found that such pre-shock perturbations can excite the fluid
instabilities efficiently and hence help the shock revive in core-collapse
supernovae.
