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

Abstract

Bow shock pulsar wind nebulae are observed with a variety of complex morphologies at different wavelengths, most likely due to differences in the magnetic field strength and pulsar wind geometry. Here we present a detailed analysis, showing how these differences affect the observational properties in these systems, focusing on non-thermal synchrotron emission. By adopting different prescriptions for the local emissivity, on top of the magnetic and flow patterns taken from 3D high-resolution numerical simulations in relativistic MHD, and considering various viewing angles, we try to characterize the main features of the emission and polarization, to verify if and how these can be used to get information, or to put constraints, on known objects. We found for example that conditions leading to a strong development of the turbulence in the bow shock tail produce substantial differences in the emission pattern, especially in polarized light.

Relativistic Outflows From Compact Galactic Sources

“…This escape/diffusion scenario has been further studied through MHD simulations recently (see e.g. Olmi & Bucciantini 2019), which have confirmed its viability and even explained the circumstances under which highly asymmetric counter-outflows can be produced in runaway PWNe). Recent observations of IGR J11014-6103 , however, seem to partially challenge these results, as the misaligned outflow appears to bend around the pulsar position, after which it becomes much more rectilinear.…”

3D Relativistic MHD Simulations of Pulsar Bow Shock Nebulae

“…Solutions were computed for various relative inclinations, magnetisations σ, and pulsar wind energy distributions, making sure that the dynamics was relaxed to a quasi-steady regime. For a more detailed description of the setup and of the models we refer the reader to [72,73,76], where they are discussed and presented in more details. Please nota that the density and magnetic field can be scaled arbitrarily as far as the ratio, B 2 /ρc 2 , is fixed.…”

“…The first 3D models of BSPWNe were presented by [32] but limited to the classical HD regime. Only recently 3D MHD simulations have been presented in the correct relativistic regime [33,[71][72][73]. More recently [74,75], using a simplified, axisymmetric laminar semi-analytic model tuned on numerical simulations, have investigated for then first time how different magnetic field geometry act on the observed non-thermal synchrotron emission and polarisation, and on the propagation of high energy particles, showing the role played by current sheets and current layers.…”

“…Here we present the result of a detailed study of the dynamics, emission, and particle propagation properties of BSPWNe, done using 3D relativistic MHD simulations [72][73][74][75][76]. Various configurations were considered in terms of inclinations of the magnetic field with respect to the pulsar spin-axis, wind magnetisation, pulsar wind energy distribution, particle acceleration properties, in order to have a sample as complete as possible of the interaction conditions.…”

Fast moving pulsars as probes of interstellar medium

“…Typically, these velocities are much larger than the sound speeds in the interstellar medium (ISM), c s, ism ∼ 10 − 100 km s −1 . The interaction of the fast mowing pulsar wind with the ISM produces a bow-shock nebula with an extended tail (see Barkov et al 2019a;Olmi & Bucciantini 2019).…”