PSR B0329+54: Substructure in the scatter-broadened image discovered with RadioAstron on baselines up to 330,000 km

TL;DR

This study used RadioAstron to resolve the scatter-broadened image of pulsar PSR B0329+54, revealing substructure caused by interstellar medium turbulence, and provided new measurements of scattering disk size and location.

Contribution

First direct detection of substructure in the scatter-broadened image of PSR B0329+54 using space-ground interferometry at 324 MHz.

Findings

Detected substructure within the scatter-broadened image.

Measured scattering disk size as 4.8±0.8 mas.

Estimated the scattering screen is 0.6±0.1 of the distance to the pulsar.

Abstract

We have resolved the scatter-broadened image of PSR B0329+54 and detected substructure within it. These results are not influenced by any extended structure of a source but instead are directly attributed to the interstellar medium. We obtained these results at 324 MHz with the ground-space interferometer RadioAstron which included the space radio telescope (SRT), ground-based Westerbork Synthesis Radio Telescope and 64-m Kalyazin Radio Telescope on baseline projections up to 330,000 km in 2013 November 22 and 2014 January 1 to 2. At short 15,000 to 35,000 km ground-space baseline projections the visibility amplitude decreases with baseline length providing a direct measurement of the size of the scattering disk of 4.8$\pm$0.8 mas. At longer baselines no visibility detections from the scattering disk would be expected. However, significant detections were obtained with visibility amplitudes of 3 to 5% of the maximum scattered around a mean and approximately constant up to 330,000 km. These visibilities reflect substructure from scattering in the interstellar medium and offer a new probe of ionized interstellar material. The size of the diffraction spot near Earth is 17,000$\pm$3,000 km. With the assumption of turbulent irregularities in the plasma of the interstellar medium, we estimate that the effective scattering screen is located 0.6$\pm$0.1 of the distance from Earth toward the pulsar.