Size of the Vela Pulsar's Radio Emission Region: 500 Kilometers

We use interstellar scattering of the Vela pulsar to determine the size of its emission region. We find that radio-wave scattering in the Vela supernova remnant broadens the source by 3.3 ± 0.2 mas × 2.0 ± 0.1 mas, with the major axis at a position angle of 92° ± 10°. From the modulation of the pulsar's scintillation, we infer a size of 500 km for the pulsar's emission region, with an estimated uncertainty of about a factor of 2, including systematic errors. We suggest that radio-wave refraction within the pulsar's magnetosphere may plausibly explain this size. © 1997. The American Astronomical Society. All rights reserved.