Amplitude Variations in Pulsed Radio Sources

Abstract

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.