Long-Term Scintillation Studies of Pulsars: III. Testing Theoretical Models of Refractive Scintillation

摘要

Refractive interstellar scintillation (RISS) is thought to be the causebehind a variety of phenomena seen at radio wavelengths in pulsars and compactradio sources. Though there is substantial observational data to supportseveral consequences of it, the quantitative predictions from theories have notbeen thoroughly tested. In this paper, data from our long-term scintillationstudy of 18 pulsars are used to test the predictions. The fluctuations ofdecorrelation bandwidth ($u_d$), scintillation time scale ($au_d$) and fluxdensity (F) are examined for their cross-correlations and compared with thepredictions. The theory predicts a strong correlation between $u_d$ and$au_d$, and strong anti-correlations between $u_d$ and F, and $au_d$ andF. For 5 pulsars, we see a reasonable agreement. There is considerabledifficulty in reconciling the results for the rest of the pulsars. Our analysisshows the underlying noise sources can sometimes reduce the correlation, butcannot cause an absence of correlation. It is also unlikely that the poor fluxcorrelations arise from a hitherto unrecognized intrinsic flux variations. ForPSR B0834+06, which shows anomalous behaviour of persistent drift slopes,positive correlation is found between $au_d$ and the drift-corrected $u_d$.Many pulsars show an anti-correlation between $u_d$ and the drift slope, andthis is in accordance with the simple models of RISS. The detections ofcorrelated variations of observables and a reasonable agreement between thepredicted and measured correlations for some pulsars confirm RISS as theprimary cause of the observed fluctuations. However, the complexity seen withthe detailed results suggests the necessity of more comprehensive theoreticaltreatments for describing refractive fluctuations and their correlations.