The major role of eccentricity in the evolution of colliding pulsar-stellar winds

TL;DR

This study uses a semi-quantitative 3D scheme to analyze how eccentricity influences the large-scale evolution and collimation of colliding pulsar-stellar winds in binary systems, revealing that higher eccentricity leads to more collimated and less mixed flows.

Contribution

First analysis of the impact of orbital eccentricity on the large-scale structure of pulsar-stellar wind interactions using a quasi 3D model.

Findings

Higher eccentricity causes flows to behave like a one-sided outflow.

Eccentricity values ≥ 0.75 lead to highly collimated flows.

Low eccentricity systems exhibit more stochastic wind mixing.

Abstract

Binary systems that host a massive star and a non-accreting pulsar can be powerful non-thermal emitters. The relativistic pulsar wind and the non-relativistic stellar outflows interact along the orbit, producing ultrarelativistic particles that radiate from radio to gamma rays. To properly characterize the physics of these sources, and better understand their emission and impact on the environment, careful modelling of the outflow interactions, spanning a broad range of spatial and temporal scales, is needed. Full 3-dimensional approaches are very computationally expensive, but simpler approximate approaches, while still realistic at the semi-quantitative level, are available. We present here the results of calculations done with a quasi 3-dimensional scheme to compute the evolution of the interacting flows in a region spanning in size up to a thousand times the size of the binary. In particular, we analyze for the first time the role of different eccentricities in the large scale evolution of the shocked flows. We find that the higher the eccentricity, the closer the flows behave like a one-side outflow, which becomes rather collimated for eccentricity values $\gtrsim 0.75$. The simulations also unveil that the pulsar and the stellar winds become fully mixed within the grid for low eccentricity systems, presenting a more stochastic behavior at large scales than in the highly eccentric systems.