Long‐Term Scintillation Studies of Pulsars. I. Observations and Basic Results

Abstract

We report long-term scintillation observations of 18 pulsars in the dispersion measure range 3 − 35 pc cm −3 carried out from 1993 January to 1995 August using the Ooty Radio Telescope at 327 MHz. These observations were made with the aim of studying refractive effects in pulsar scintillation, and obtaining reliable estimates of diffractive and refractive scintillation properties. Dynamic scintillation spectra of pulsars were regularly monitored at 10 − 90 epochs spanning 100 − 1000 days. Significant changes are observed in the dynamic spectra over time scales as short as a few days. Large-amplitude fluctuations are observed in quantities such as decorrelation bandwidth, scintillation time scale, drift rate, and flux density. Several pulsars show organized features such as drifting bands in a highly pronounced manner. For some pulsars, gradual and systematic variations are seen in the drift rate of patterns which undergo several sign reversals during the observing time spans. Anomalous behaviour such as persistent drifts lasting over many months are seen for PSRs B0834+06 and B1919+21. Four pulsars were studied for 2 − 4 well separated observing sessions, each lasting over ∼ 100 days. In some cases, significant variations are seen in the average scintillation properties and/or flux densities between successive observing sessions. From our data, we have been able to obtain more accurate and reliable estimates of scintillation properties and flux densities than those from the earlier observations, by averaging out the fluctuations due to refractive scintillation effects. These measurements are used to derive parameters such as the strength of scattering and scintillation speeds. The scintillation speed estimates are found to be reasonably good indicators of proper motion speeds of pulsars. The present measurements are compared with earlier measurements and the long-term stability of scintillation properties and flux densities is discussed.

Diffractive and refractive timescales at 4.8 GHz in PSR B0329+54

“…It has to be noted that in case of three of the four parameters (with the m RISS being the only exception), these discrepancies cannot be attributed to poor quality Table 4. Theoretical and observed spectral indices of scintillation parameters (Romani et al 1986;Bhat et al 1999 of frequency slopes fits for these parameters, especially that our measurements, made at the frequency of 4.8 GHz, significantly widened the frequency range, putting strong constraints on the fits.…”

“…Pulsar B0329+54 is one of the strongest radio pulsars known so far, and scintillations of its radiation were analysed at various A66, page 6 of 10 Bhat et al (1999) at 327 MHz, Gupta et al (1994) at 408 MHz, Stinebring et al (1996) at 610 MHz, Wang et al (2005) at 1.5 GHz, and this paper at 4.8 GHz. The solid line presents the fit to observed data.…”

Measurements of the interstellar turbulent plasma spectrum of PSR B0329+54 using multi-frequency observations of interstellar scintillation

“…We may conclude therefore that the refractive effect dominates over all ranges of the variation of ∆ f . It is interesing to compare the angular refractive effect discussed above with the slanting features which are sometimes observed in the dynamical spectra of pulsars (see, for example, Rickett 1969;Gupta et al 1994;Stinebring et al 1996;Bhat et al 1999). The angular refractive effect, which is evident in the frequency correlation function of intensity fluctuations, is stable over more than 15 years, because the time lag between the observations at 102 and 610 MHz as well as 5 GHz is about 15 years.…”

A study of the long-term flux density variation of PSRs B0329+54 and B1508+55

“…LaBrecque et al (1994) studied 20 pulsars at 430 MHz observed over a 4 yr span. Bhat et al (1999a) presented results of a project of dynamic-scintillation-spectra monitoring of 18 pulsars at 327 MHz during a 3 yr period. They studied refractive effects in pulsar scintillation and obtained reliable estimates of diffractive scintillation properties.…”