Multiple imaging of pulsars by refraction in the interstellar medium

The authors demonstrate, using dynamic spectra of interstellar scintillations, that pulsar images are sometimes multiple and that images change on time scales of days to months. Component separations as large as 4 mas at 430 MHz are twice the scattering diameter of each component which, in turn, is at least 104times the intrinsic source size. The authors discuss the implications of the results for VLBI, for timing measurements of pulsars, and for the form of the interstellar electron-density wavenumber spectrum.