The radio pulses from the sources discovered by Hewish et al.1,2 show extremely regular repetition rates but quite erratic amplitude fluctuations, over time scales ranging from less than a second1 to hours3 or even days1. The rapid pulse-to-pulse variations appear to be well correlated on different frequencies3, and, as will be shown, they are most probably an intrinsic property of the source. The long-period variations show little, if any, correlation between different frequencies3, and it seems difficult to imagine a source of wide-band pulses which have a very complex spectrum that is preserved over hundreds or thousands of pulses. Such complex frequency structure rather suggests that the emission process is modulated by interference phenomena, either between a number of coherent pulsed sources on the surface of a star, or else between a number of images of the source caused by irregular refraction in an interstellar medium. The latter possibility is considered in this article.
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- 5.Little, L. T., Plan. Spa. Sci. (in the press).Google Scholar