The Major Role of Eccentricity in the Evolution of Colliding Pulsar-Stellar Winds

Maxim V Barkov,Valenti Bosch-Ramon

doi:10.3390/universe7080277

Maxim V Barkov, Valenti Bosch-Ramon

Open Access

https://doi.org/10.3390/universe7080277

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Journal: Universe	Publication Date: Jul 31, 2021
Citations: 4	License type: CC BY 4.0

Affiliation: Institute of Astronomy, Russian Academy of Sciences

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 modeling of the outflow interactions, spanning a broad range of spatial and temporal scales, is needed. Full three-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 three-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 ≳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.

Highlights

Binary systems hosting a massive star and a non-accreting pulsar, or pulsar highmass binaries (PHMB), can be powerful sources of gamma rays
The radiation is produced through the interaction of a relativistic pulsar wind and the outflows ejected by the star: massive stars produce strong non-relativistic winds of supersonic nature and, in cases of very fast stellar rotation, quasi-Keplerian equatorial disks that flow outwards at subsonic speeds
These outflows interact with the pulsar wind and, later, on interstellar matter in a process in which ultrarelativistic particles are accelerated and produce emission from radio to gamma rays, see, e.g., [4,5,6,7,8,9,10,11,12,13,14,15]

Summary

Introduction

Binary systems hosting a massive star and a non-accreting pulsar, or pulsar highmass binaries (PHMB), can be powerful sources of gamma rays. The radiation is produced through the interaction of a relativistic pulsar wind and the outflows ejected by the star: massive stars produce strong non-relativistic winds of supersonic nature and, in cases of very fast stellar rotation, quasi-Keplerian equatorial disks (or decretion disks) that flow outwards at subsonic speeds. Orbital motion is to be included in the colliding-wind picture, which makes a Coriolis force appear, a force that affects differently the pulsar and the stellar outflows due to the large relative velocity and density contrast. This differential Coriolis effect makes the stellar wind push on the shocked pulsar wind against the orbital rotation sense, creating a strong deflection of the interaction structure in that direction, and triggering a strong lateral shock in the shocked pulsar wind.

Numerical Model

Results

Summary and Discussion