Size of the Vela Pulsar's Radio Emission Region: 500 km
  We use interstellar scattering of the Vela pulsar to determine the size of its emission region. From interferometric phase variations on short baselines, we find that radio-wave scattering broadens the source by 3.4+/-0.3 milliarcseconds along the major axis at position angle 81+/-3 degrees. The ratio of minor axis to major axis is 0.51+/-0.03. Comparison of angular and temporal broadening indicates that the scattering material lies in the Vela-X supernova remnant surrounding the pulsar. From the modulation of the pulsar's scintillation on very short baselines, we infer a size of 500 km for the pulsar's emission region. We suggest that radio-wave refraction within the pulsar's magnetosphere may plausibly explain this size. 
C.R. Gwinn, M.J. Ojeda, M.C. Britton, J.E. Reynolds, D.L. Jauncey,   E.A. King, P. M. McCulloch, J.E.J. Lovell, C.S. Flanaga...