Double-lens Scintillometry: The variable scintillation of pulsar B1508+55

TL;DR

This study observes pulsar B1508+55's scintillation over two years, revealing a transition in scattering arc features that indicates a two-screen scattering geometry, and develops novel analytical methods for modeling such phenomena.

Contribution

It introduces a new two-screen scattering model and innovative analysis methods, enhancing understanding of pulsar scintillation and scattering geometries.

Findings

Detected a transition from stripe-like to parabolic arclets in scintillation.

Discovered evidence for a two-screen scattering geometry.

Developed transferable analytical methods for pulsar scintillation analysis.

Abstract

We report on observations of PSR B1508+55's scintillation at the Effelsberg 100-m telescope spanning from early 2020 to early 2022. In the autumn of 2020, close to the time the pulsar was predicted to cross echoes in its pulse profile, a sudden transition in the scintillation arcs from peculiar stripe-like features to parabolic arclets was observed. To infer a geometric model of the scattering we measure the effects of the annual velocity curve of Earth, of the relative movement of the line of sight, and of the projection of points on a second scattering screen and develop novel methods to do so. The latter phenomenon was discovered by this study and strongly indicates a two-screen scattering geometry. We derive an analytical two-screen model and demonstrate in a Markov Chain Monte Carlo analysis as well as simulations that it can be successfully applied to explain the observations by interpreting the transition as a change of relative amplitudes of images as well as a shift in the orientation of anisotropy. The collection of methods we demonstrate here is transferable to other pulsars with the potential to strongly improve constraints on scattering models.