Size of the Vela Pulsar's Emission Region at 18 cm Wavelength

TL;DR

This study measures the Vela pulsar's emission region size at 18 cm wavelength, revealing phase-dependent variations and demonstrating a method to detect finite emission sizes using scintillation effects.

Contribution

It introduces a novel technique to infer pulsar emission region size from scintillation signatures and provides detailed measurements across pulse phases.

Findings

Emission region size varies with pulse phase.

Size decreases near pulse peak and increases at edges.

Detected a characteristic W-shaped scintillation signature.

Abstract

We present measurements of the linear diameter of the emission region of the Vela pulsar at observing wavelength lambda=18 cm. We infer the diameter as a function of pulse phase from the distribution of visibility on the Mopra-Tidbinbilla 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 equivalent full width at half maximum of the pulsar's emission region decreases from more than 400 km early in the pulse to near zero at the peak of the pulse, and then increases again to approximately 800 km near the trailing edge. We discuss possible systematic effects, and compare our work with previous results.