Pulsar Scintillation and the Local Bubble

We present here the results from an extensive scintillation study of twentypulsars in the dispersion measure (DM) range 3 - 35 pc cm^-3 caried out usingthe Ooty Radio Telescope (ORT) at 327 MHz, to investigate the distribution ofionized material in the local interstellar medium. Observations were madeduring the period January 1993 to August 1995, in which the dynamicscintillation spectra of these pulsars were regularly monitored over 10 - 90epochs spanning 100 days. Reliable and accurate estimates of strengths ofscattering have been deduced from the scintillation parameters averaged out fortheir long-term fluctuations arising from refractive scintillation (RISS)effects. Our analysis reveals several anomalies in the scattering strength,which suggest tht the distribution of scattering material in the Solarneighborhood is not uniform. We have modelled these anomalous scattering effects in terms ofinhomogeneities in the distribution of electron dnsity fluctuations in thelocal interstellar medium (LISM). Our model suggests the presence of a lowdensity bubble surrounded by a shell of much higher density fluctuations. Weare able to put constraints on geometrical and scattering properties of such astructure, and find it to be morphologically similar to the Local Bubble knownfrom other studies.Comment: 35 pages, 12 figure