LONG-TERM PULSAR FLUX MONITORING AND REFRACTIVE INTERSTELLAR SCINTILLATION

We have observed the flux densities of 14 pulsars for over 1 year at an observing frequency of 610 MHz, using an NRAO 26 m telescope in Green Bank, West Virginia. The observed time scales for long-term flux variation for seven pulsars are in good agreement with refractive scintillation theory. Four pulsars, including the Vela pulsar, have observed time scales that are in poor agreement with theoretical predictions. Pulsars predicted to have extremely long refractive scintillation time scales are observed to have stable fluxes. These pulsars therefore have intrinsically stable luminosities. In spite of our sample having a wide range of dispersion measures (43-475 pc cm-3), we find no scintillation modulation depth greater than 0.4. Our observations preclude models for the interstellar medium having a spectrum for electron density inhomogeneities P(q) = C(n)2q--beta with beta greater than 4, and are inconsistent with the presence of an inner scale as large as 10(9) m. Our results are best described by a Kolmogorov spectrum of electron density inhomogeneities.