Optical study of pulsars (Optical photometry)

The Crab Pulsar emits radiation at all wavelengths from radio to extreme γ-rays including the optical. We have performed extremely high time resolution multicolor photometry of the Crab Pulsar at optical wavelengths to constrain the high energy emission models for pulsars. Our observations with 1 microsecond time resolution are a factor of 20 better than the previous best observations.; We have completely resolved the peak of the main pulse of the Crab Pulsar in optical passbands. The peaks of the main pulse and the interpulse move smoothly from the rising branch to the falling branch with neither a flat top nor a cusp. We find that the peak of the Crab Pulsar main pulse in the B band arrives 140 microseconds before the peak of the radio pulse.; The color of the emission changes across the phase. The maximum variation in the color ratio is about 25%. The bluest color occurs in the bridge region between the main pulse and the interpulse. The Crab Pulsar has faded by 2 ± 2.8% since the previous observations in 1991 using the same instrument.; The statistics of photon arrival times are consistent with atmospheric scintillation causing most of the variations in addition to the mean pulse variations in the shape. However, the autocorrelation function (ACF) of the Crab Pulsar light curve shows extra correlations at very short time scales. We identify two time scales, one at about 20 microseconds and another one at about 1000 microseconds at which we observe a break in the ACF. We conclude that these short timescale correlations are internal to the pulsar.; We attribute the extra correlation observed in our data to microstructures. This is the first time evidence for microstructures has been observed outside the radio wavelengths. The upturn in the ACF at short time scales depends on the color. The U band shows about 10% more correlation at short time scales while the R band shows only about 3% change.; We have also observed the young X-ray pulsar PSR 0656+14 at optical wavelengths. We do not detect any periodicity at the radio pulsar period up to a limiting magnitude of about 26.5.