Pulsar Scintillation and the Local Bubble

Abstract

We present the results from an extensive scintillation study of 20 pulsars in the dispersion measure range 3-35 pc cm-3, carried out using the Ooty Radio Telescope at 327 MHz, to investigate the distribution of ionized material in the local interstellar medium (LISM). Observations were made during the period 1993 January-1995 August, in which the dynamic scintillation spectra of these pulsars were regularly monitored over 10-90 epochs spanning ~100 days. Reliable and accurate estimates of strengths of scattering have been deduced from the scintillation parameters, averaged out for their long-term fluctuations arising from refractive scintillation effects. Our analysis reveals several anomalies in the scattering strength, which suggest that the distribution of scattering material in the solar neighborhood is not uniform. We have modeled these anomalous scattering effects in terms of inhomogeneities in the distribution of electron density fluctuations in the LISM. Our model suggests the presence of a low-density bubble surrounded by a shell of much higher density fluctuations. We are able to put some constraints on geometrical and scattering properties of such a structure and find it to be morphologically similar to the Local Bubble known from other studies.