Periodic interstellar scintillation variations of PSRs~J0613$-$0200 and J0636+5128 associated with the Local Bubble shell

TL;DR

This study analyzes annual and orbital variations in interstellar scintillation of two pulsars, revealing their scattering screens are located within the Local Bubble shell, and employs Bayesian methods to interpret anisotropic scattering models.

Contribution

It provides the first detailed measurements of scattering screen distances and anisotropy for these pulsars, linking them to the Local Bubble shell.

Findings

Scattering screen distances are approximately 316 pc and 262 pc.

PSR J0613-0200 shows mildly anisotropic scattering.

PSR J0636+5128 exhibits extremely anisotropic scattering.

Abstract

Annual variations of interstellar scintillation can be modelled to constrain parameters of the ionized interstellar medium. If a pulsar is in a binary system, then investigating the orbital parameters is possible through analysis of the orbital variation of scintillation. In observations carried out from 2011 January to 2020 August by the European Pulsar Timing Array radio telescopes, PSRs~J0613$-$0200 and J0636+5128 show strong annual variations in their scintillation velocity, while the former additionally exhibits an orbital fluctuation. Bayesian theory and Markov-chain-Monte-Carlo methods are used to interpret these periodic variations. We assume a thin and anisotropic scattering screen model, and discuss the mildly and extremely anisotropic scattering cases. PSR~J0613$-$0200 is best described by mildly anisotropic scattering, while PSR~J0636+5128 exhibits extremely anisotropic scattering. We measure the distance, velocity and degree of anisotropy of the scattering screen for our two pulsars, finding that scattering screen distances from Earth for PSRs~J0613$-$0200 and J0636+5128 are 316$^{+28}_{-20}$\,pc and 262$^{+96}_{-38}$\,pc, respectively. The positions of these scattering screens are coincident with the shell of the Local Bubble towards both pulsars. These associations add to the growing evidence of the Local Bubble shell as a dominant region of scattering along many sightlines.