The $\theta$-$\theta$ Diagram: Transforming pulsar scintillation spectra to coordinates on highly anisotropic interstellar scattering screens

TL;DR

This paper presents a new method to analyze pulsar scintillation spectra by transforming observed data into angular coordinates on interstellar screens, revealing detailed structures and extending to 2D distributions.

Contribution

It introduces a novel transformation technique for pulsar secondary spectra, enabling mapping to interstellar scattering screens and analysis of their properties.

Findings

Transformation maps secondary spectra to angular coordinates

Method measures curvature and field amplitude of images

Extended formalism to 2D image distributions

Abstract

We introduce a novel analysis technique for pulsar secondary spectra. The power spectrum of pulsar scintillation (referred to as the "secondary spectrum") shows differential delays and Doppler shifts due to interference from multi-path propagation through the interstellar medium. We develop a transformation which maps these observables to angular coordinates on a single thin screen of phase-changing material. This transformation is possible without degeneracies in the case of a one-dimensional distribution of images on this screen, which is often a successful description of the phenomenon. The double parabolic features of secondary spectra are transformed into parallel linear features, whose properties we describe in detail. Furthermore, we introduce methods to measure the curvature parameter and the field amplitude distribution of images by applying them to observations of PSR B0834+06. Finally, we extend this formalism to two-dimensional distributions of images on the interstellar screen.