High time resolution observations of the Vela pulsar

We present high time resolution observations of single pulses from the Vela pulsar (PSR B0833-45) made with a baseband recording system at observing f requencies of 660 and 1413 MHz. We have discovered two startling features i n the 1413 MHz single-pulse data. The first is the presence of giant microp ulses that are confined to the leading edge of the pulse profile. One of th ese pulses has a peak flux density in excess of 2500 Jy, more than 40 times the integrated pulse peak. The second new result is the presence of a larg e-amplitude Gaussian component on the trailing edge of the pulse profile. T his component can exceed the main pulse in intensity but is switched on onl y relatively rarely. Fluctuation spectra reveal a possible periodicity in t his feature of 140 pulse periods. Unlike the rest of the profile, this comp onent has low net polarization and emits predominantly in the orthogonal mo de. This feature appears to be unique to the Vela pulsar. We have also dete cted microstructure in the Vela pulsar for the first time. These same featu res are present in the 660 MHz data. We suggest that the full width of the Vela pulse profile might be as large as 10 ms but that the conal edges emit only rarely.