Size and Motion of the Interstellar Scintillation Pattern from Observations of CP 1133

Abstract

THE time variations of the intensity of pulsar radiation at radio frequencies may be described by the superposition of short and long term fluctuations. Scheuer1 has shown that the short term fluctuations are most probably intrinsic to the source, and both Scheuer and Salpeter2 have suggested that the long term fluctuations may be scintillation caused by irregularities in the interstellar medium. B. J. R. (ref. 3 and unpublished work) provided some evidence for the interstellar scintillation hypothesis when he observed a correlation between dispersion measure and the characteristic bandwidth over which the intensity variations are correlated. Additional evidence has been provided by Lang4, who has shown that the long term variations of four pulsars have power spectra, modulation indices, frequency distributions and decorrelation frequencies which are consistent with the predictions of scintillation theory.