The spherical space form conjecture (now theorem) asserts that every finite group acting on the 3-spere is conjugate to a subgroup of SO(4). Is the action assumed to be smooth? Can anything similar be said for topological actions? Also, I would appreciate a reference about the spherical space form conjecture.

The spherical space form conjecture (now theorem) asserts that every finite group acting on the 3-sphere is conjugate to a subgroup of $\mathrm{SO}(4)$. Is the action assumed to be smooth? Can anything similar be said for topological actions? Also, I would appreciate a reference about the spherical space form conjecture.