IF the recently reported1,2 0.5-ms-period pulsed optical signal from the direction of supernova 1987A originated in a young neutron star, its interpretation as a rotational period has difficulties. The surface magnetic field would have to be much lower than expected, and the high rotation rate may rule out preferred nuclear equations of state3,4. Here we point out that a remnant radial vibration of a neutron star, excited in the supernova event, may survive for several years with about the observed (gravitationally red-shifted) period. Heavy ions at the low-density stellar surface, periodically shocked by the vibration, may efficiently produce narrow pulses of optical cyclotron radiation in a surface field of ∼1012 gauss. These pulses may be modulated only slightly by a much slower stellar rotation because of the nearly isotropic emission mechanism and smearing from the strong gravitational bending of light rays5,6. We do not attempt to explain the reported1 8-hour modulation, which may be a result of timing noise (ref. 7 and J. Katz, preprint).