Search for discrete refractive scattering events

We have searched for discrete refractive scattering events (including effec ts due to possible non-multiple diffractive scattering) at meter wavelength s in the direction of two close by pulsars B0950+08 and B1929+10, where we looked for spectral signatures associated with the multiple imaging of puls ars due to scattering in the interstellar medium. We do not find any signat ures of such events in the direction of either source over a spectral perio dicity range of 50 KHz to 5 MHz. Our analysis puts strong upper limits on t he column density contrast associated with a range of spatial scales of the interstellar electron density irregularities along these lines of sight.