PSR B0329+54: Statistics of Substructure Discovered within the Scattering Disk on RadioAstron Baselines of up to 235,000 km

TL;DR

This paper reports the discovery of fine-scale substructure within the scattering disk of pulsar PSR B0329+54 using RadioAstron, revealing two distinct scattering scales in the interstellar medium through high-resolution interferometric observations.

Contribution

It presents the first detailed characterization of substructure within the scattering disk at unprecedented baselines, identifying two exponential scattering scales and interpreting their physical origins.

Findings

Two exponential scattering scales with delays of 4.1 and 23 microseconds.

The longer scattering tail contains 38% of the scattered power.

Detection of discrete spikes in visibility indicating fine-scale substructure.

Abstract

We discovered fine-scale structure within the scattering disk of PSR B0329+54 in observations with the RadioAstron ground-space radio interferometer. Here, we describe this phenomenon, characterize it with averages and correlation functions, and interpret it as the result of decorrelation of the impulse-response function of interstellar scattering between the widely-separated antennas. This instrument included the 10-m Space Radio Telescope, the 110-m Green Bank Telescope, the 14x25-m Westerbork Synthesis Radio Telescope, and the 64-m Kalyazin Radio Telescope. The observations were performed at 324 MHz, on baselines of up to 235,000 km in November 2012 and January 2014. In the delay domain, on long baselines the interferometric visibility consists of many discrete spikes within a limited range of delays. On short baselines it consists of a sharp spike surrounded by lower spikes. The average envelope of correlations of the visibility function show two exponential scales, with characteristic delays of $\tau_1=4.1\pm 0.3\ \mu{\rm s}$ and $\tau_2=23\pm 3\ \mu{\rm s}$, indicating the presence of two scales of scattering in the interstellar medium. These two scales are present in the pulse-broadening function. The longer scale contains 0.38 times the scattered power of the shorter one. We suggest that the longer tail arises from highly-scattered paths, possibly from anisotropic scattering or from substructure at large angles.