Simultaneous Dual‐Frequency Observations of Giant Pulses from the Crab Pulsar

Simultaneous measurements of giant pulses from the Crab pulsar were taken attwo widely spaced frequencies using the real-time detection of a giant pulse at1.4 GHz at the Very Large Array to trigger the observation of that same pulseat 0.6 GHz at a 25-m telescope in Green Bank, WV. Interstellar dispersion ofthe signals provided the necessary time to communicate the trigger across thecountry via the Internet. About 70% of the pulses are seen at both 1.4 GHz and0.6 GHz, implying an emission mechanism bandwidth of at least 0.8 GHz at 1 GHzfor pulse structure on time scales of one to ten microseconds. The arrival times at both frequencies display a jitter of 100 microsecondswithin the window defined by the average main pulse profile and are tightlycorrelated. This tight correlation places limits on both the emission mechanismand on frequency dependent propagation within the magnetosphere. At 1.4 GHz the giant pulses are resolved into several, closely spacedcomponents. Simultaneous observations at 1.4 GHz and 4.9 GHz show that thecomponent splitting is frequency independent. We conclude that the multiplicityof components is intrinsic to the emission from the pulsar, and reject thehypothesis that this is the result of multiple imaging as the signal propagatesthrough the perturbed thermal plasma in the surrounding nebula. At both 1.4 GHzand 0.6 GHz the pulses are characterized by a fast rise time and an exponentialdecay time which are correlated. The pulse broadening with its exponentialdecay form is most likely the result of multipath propagation in interveningionized gas.Comment: LaTeX, 18 pages, 7 figures, accepted for publication in The Astrophysical Journa