Spaced Receiver Observations of Pulsed Radio Sources
The apparently random fluctuations in the amplitude of pulsed radio sources1 contrasts strikingly with the strictly periodic nature of the pulses1,2. This behaviour suggests that the fluctuations do not originate in the source itself but rather are imposed by the intervening medium. Scheuer3, however, has argued that the amplitude variations cannot be scintillations produced by either the general interstellar medium or the interplanetary medium. A spaced receiver experiment which we carried out in May 1968 provides experimental confirmation of Scheuer’s conclusion, at least for those fluctuations having quasi-periods of up to several minutes’ duration. Our results demonstrate that there is no detectable time displacement between the amplitude variations at the spaced receivers. This provides direct evidence that variations in pulse amplitude are imposed at or naer the source itselt.