TEMPORAL VARIATION OF PULSAR DISPERSION MEASURE

A new theory is proposed to explain the temporal variation of the disp ersion measure of pulsars. In view of the extremely high values of the observed radio luminosity, the pulsar radio waves in the vicinity of the source region within a pulsar magnetosphere obey a nonlinear dispe rsion relation which depends on the pulse amplitude. Hence the observe d DM variations might be due to the influence of the pulse amplitude o n the dispersion relation. It is shown that there is a correlation bet ween the DM fluctuation and the radio luminosity, suggesting that the variations of the pulse intensity may be one of the important causes o f DM fluctuations.