C. R. Gwinn, M. D. Johnson, J. E. Reynolds, D. L. Jauncey, A. K. Tzioumis, H. Hirabayashi, H. Kobayashi, Y. Murata, P. G. Edwards, S. Dougherty, B. Carlson, D. del Rizzo, J. F. H. Quick, C. S. Flanagan, P. M. McCulloch
We present measurements of the linear diameter of the emission region of the Vela pulsar at lambda=18 cm observing wavelength. We assume a Gaussian distribution of visibility for the source, with the same aspect ratio as the scattering disk. We infer the diameter as a function of pulse phase from the distribution of visibility on the Tidbinbilla-Mopra baseline. As we demonstrate, in the presence of strong scintillation, finite size of the emission region produces a characteristic W-shaped signature in the projection of the visibility distribution onto the real axis. This modification involves heightened probability density near the mean amplitude, decreased probability to either side, and a return to the zero-size distribution beyond. We observe this signature with high statistical significance, as compared with the best-fitting zero-size model, in many regions of pulse phase. We find that the size of the pulsar's emission region, expressed as full width at half maximum of the best-fitting circular Gaussian distribution, decreases from more than 400 km early in the pulse to near zero at the peak of the pulse, and then increases again to about 800 km near the trailing edge. We discuss possible systematic effects, and compare our work with previous results.
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http://arxiv.org/abs/1208.0040
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