Well I am not sure. In the process whereby a
neutron star is made due to the collapse of a
white dwarf star, the conservation of angular
momentum insures that AS THE WHITE DWARF SHRINKS
TO BECOME A NEUTRON STAR, its rotation or SPIN
rate will go up by millions to billions. So even
if the white dwarf is very slowly spinning, the NS
will spin millions to billions of time faster.
Strong magnetic effects may also complicate the
picture.So a non rotating NS probably cant exist.