Besides pre-ejected material, what intrinsic factor related to the progenitor star can cause a supernova remnant to be non-spherical?

Answer

Rapid rotation or strong magnetic fields channeling the outflow.

The explosion mechanism itself can be asymmetric due to factors like rapid rotation favoring ejection in certain directions, or strong magnetic fields channeling the outflow into bipolar structures or jets.

Besides pre-ejected material, what intrinsic factor related to the progenitor star can cause a supernova remnant to be non-spherical?
starsexpansionastrophysicssupernova remnantsshock waves