Full-3D relativistic MHD simulations of bow shock pulsar wind nebulae: dynamics

Abstract

Bow shock pulsar wind nebulae (BSPWNe) are know to show a large variety of shapes and morphologies, both when comparing different objects, and for the same object in different energy bands. It is unclear if such a variety is related to differences in the pulsar wind properties, or to differences in the conditions of the ambient medium. We present here a set of full three-dimensional, relativistic and magneto-hydrodynamic simulations of BSPWNe, with the intention of determining how differences in the injection conditions by the pulsar wind reflect in the nebular dynamics. To achieve a good coverage of the available parameter space we have run several simulations varying those parameters that are most representative of the wind properties: the latitudinal anisotropy of the wind energy flux with respect to the pulsar spin axis, the level of magnetization, the inclination of the pulsar spin axis with respect to the pulsar direction of motion. We have followed the dynamics in these systems, not just in the very head, but also in the tail, trying to assess if and how the system retains memory of the injection at large distances from the pulsar itself. In this paper we focus our attention on the characterization of the fluid structure and magnetic field properties. We have tried to evaluate the level of turbulence in the tail, and its relation to injection, the survival of current sheets, and the degree of mixing between the shocked ambient medium and the relativistic pulsar wind material.

GeV–TeV Cosmic-Ray Leptons in the Solar System from the Bow Shock Wind Nebula of the Nearest Millisecond Pulsar J0437–4715

“…A distinctive feature of the suggested model is that the absolute fluxes of the leptons accelerated in the nebula of PSR J0437-4715 are derived from the model of its synchrotron emission. The model employs the assumptions about the structure of the plasma flows and the magnetic field strength in the nebula (of a few tens of µG) consistent with the recent numerical MHD simulations by Barkov et al (2019) and Olmi & Bucciantini (2019). Comparison of the model predictions with the optical, far-ultraviolet, and X-ray observations of PSR J0437-4715 and its nebula (see Rangelov et al 2016) allows us to estimate the absolute fluxes of CR leptons accelerated in the nebula.…”

Full-3D relativistic MHD simulations of bow shock pulsar wind nebulae: emission and polarization

“…In this manuscript we have studied the emission and polarimetric properties of BSPWNe based on the high resolution numerical models presented and discussed in our previous work Paper I (Olmi & Bucciantini 2019), investigating and analyzing a large set of different geometries of the BSPWNe.…”

“…However only recently results from the first 3D simulations of BSPWNe in the fully relativistic MHD regime were presented by Barkov, Lyutikov & Khangulyan (2019), where the authors investigate the morphology resulting from a few different assumptions for the magnetic field geometry and properties of the ambient medium. At the same time in Olmi & Bucciantini (2019), Paper I hereafter, we presented a large set of 3D relativistic MHD simulations performed with adaptive mesh refinement (AMR) to improve the numerical resolution at the bow shock head, in an attempt to sample as much as possible the parameter space characteristic of these systems. Different models for the pulsar wind were taken into account, implementing both isotropic and anisotropic distribution of the energy flux, with diverse values of the initial magnetization, and defining a set of various geometries by varying the inclination of the pulsar spin-axis with respect to the pulsar kick velocity.…”

PHEMTO: the polarimetric high energy modular telescope observatory

“…The wide variety of morphology observed is likely explained by the relative angles of the pulsar spin axis, kick direction, and the magnetic axis and wind energy flux. 3D MHD simulations have only recently attempted to assess the role of these parameters [4,76]. High spatial resolution X-ray polarimetry is required to constrain the magnetic configuration and thus assess the important misalignment between spin axis and magnetic axis originating in the stellar collapse (see Section 2.3.2).…”