Absolute time-of-arrival measurements of optical pulses from the Crab pulsar.

An attempt is made to understand the characteristics of pulsar slowdown in terms of various possible emission mechanisms. Though magnetic-dipole radiation seems to be dominant, the deviations from a pure dipolar decay are large compared with errors in measurement and indicate the presence of more complicated braking mechanisms, small fluctuations, and major "jumps", or period discontinuities. Some rapid-relaxation effect is evident following the discontinuous jump in period in September 1969, but there is no evidence of the quasi-sinusoidal behaviour reported before the jump by Arecibo.

Optical Search for Pulsations from Pulsating Radio Source CP 1919.

Optical observations of the 18th magnitude blue star and of the faint red object in the approximate location of the pulsating radio source CP 1919 disclose no pulsations of visible light, in a mode similar to that of the radio pulsations, of more than 0.4 percent or 0.8 percent, respectively, of the total visible output; or, for a sinusoidal modulation with the same period, no more than a 4-percent, or 8-percent, root-mean-square intensity fluctuation.