General relativistic monopole magnetosphere of neutron stars: a pseudo-spectral discontinuous Galerkin approach

Mon. Not. R. Astron. Soc.

2015

Self Cite

Pulsar magnetospheres are shaped by ultra-relativistic electron/positron plasmas flowing in a strong magnetic field and subject to strong gravitational fields. The former induces magnetospheric currents and space charges responsible for the distortion of the electromagnetic field based on pure electrodynamics. The latter induces other perturbations in these fields based on space-time curvature. The force-free approximation describes the response of this magnetosphere to the presence of currents and charges and has been investigated by many authors. In this context, general relativity has been less discussed to quantify its influence on the neutron star electrodynamics. It is the purpose of this paper to compute general-relativistic force-free pulsar magnetospheres for realistic magnetic field configurations such as the inclined dipole. We performed time-dependent simulations of Maxwell equations in the 3+1 formalism of a stationary background metric in the slow-rotation approximation. We computed the resulting Poynting flux depending on the ratio R/r L and on frame-dragging through the spin parameter a s , R is the neutron star radius and r L the light-cylinder radius. Both effects act together to increase the total Poynting flux seen by a distant observer by a factor up to 2 depending on the rotation rate. Moreover we retrieve the sin 2 χ dependence of this luminosity, χ being the obliquity of the pulsar, as well as a braking index close to n = 3. We also show that the angular dependence of the Poynting flux scales like sin 2 ϑ for the aligned rotator but like sin 4 ϑ for the orthogonal rotator, ϑ being the colatitude.

“…The rotation of the neutron star is switched on smoothly as in our previous works, see Pétri (2012Pétri ( , 2014Pétri ( , 2015a. Its spin frequency increases slowly starting from zero.…”

Section: Initial Conditionssupporting

confidence: 55%

“…Galerkin methods as exposed in Pétri (2015a). This high-order finite volume method was successfully applied to the monopole and split monopole field in the force-free regime.…”

Section: Numerical Algorithmmentioning

confidence: 99%

General-relativistic force-free pulsar magnetospheres

Mon. Not. R. Astron. Soc.

2015

Self Cite

“…Vacuum solution are of the Deutsch kind but in general relativity are discussed in Pétri (2013a). The numerical simulations based on a pseudo-spectral code are described in Pétri (2014) and extended to a discontinuous Galerkin approach in Pétri (2015cPétri ( , 2016a. The conclusions drawn from special-relativistic force-free (SRFFE) simulations remain valid and the physics is not changed.…”

Section: Grffementioning

confidence: 99%

Theory of pulsar magnetosphere and wind

2016

J. Plasma Phys.

Neutron stars are fascinating astrophysical objects immersed in strong gravitational and electromagnetic fields, at the edge of our current theories. These stars manifest themselves mostly as pulsars, emitting a timely very stable and regular electromagnetic signal. Even though discovered almost fifty years ago, they still remain mysterious compact stellar objects. In this review, we summarize the most fundamental theoretical aspects of neutron star magnetospheres and winds. The main competing models explaining their radiative properties like multi-wavelength pulse shapes and spectra and the underlying physical processes such as pair creation and radiation mechanisms are scrutinized. A global but still rather qualitative picture slowly emerges thanks to recent advances in numerical simulations on the largest scales. However considerations about pulsar magnetospheres remain speculative. For instance, the exact composition of the magnetospheric plasma is not yet known. Is it solely filled with a mixture of e ± leptons or does it contain a non-negligible fraction of protons and/or ions? Is it almost entirely filled or mostly empty except for some small anecdotal plasma filled regions? Answers to these questions will strongly direct the description of the magnetosphere to seemingly contradictory results leading sometimes to inconsistencies. Nevertheless, accounts are given as to the latest developments in the theory of pulsar magnetospheres and winds, the existence of a possible electrosphere and physical insight obtained from related observational signatures of multi-wavelength pulsed emission.

“…Since then, these results have been retrieved by several other authors using different numerical approaches like finite difference/finite volume methods [34][35][36] or pseudo-spectral methods [37][38][39]. Even a combined spectral/discontinuous Galerkin method has been tried including general-relativistic effects for a monopole [40] or a dipole [41]. Some extension to dissipative magnetospheres was undertaken by [39,42,43] assuming an ad hoc prescription for the dissipation.…”

Section: Numerical Simulation Of Rotating Magnetospheresmentioning

confidence: 99%

Electrodynamics and Radiation from Rotating Neutron Star Magnetospheres

2020

Universe

Neutron stars are compact objects rotating at high speed, up to a substantial fraction of the speed of light (up to 20% for millisecond pulsars) and possessing ultra-strong electromagnetic fields (close to and sometimes above the quantum critical field of 4,4 · 10 9 T). Moreover, due to copious e ± pair creation within the magnetosphere, the relativistic plasma surrounding the star is forced into corotation up to the light cylinder where the corotation speed reaches the speed of light. The neutron star electromagnetic activity is powered by its rotation which becomes relativistic in the neighbourhood of this light cylinder. These objects naturally induce relativistic rotation on macroscopic scales about several thousands of kilometers, a crucial ingredient to trigger the central engine as observed on Earth. In this paper, we elucidate some of the salient features of this corotating plasma subject to efficient particle acceleration and radiation, emphasizing several problems and limitations concerning current theories of neutron star magnetospheres. Relativistic rotation in these systems is indirectly probed by the radiation produced within the magnetosphere. Depending on the underlying assumptions about particle motion and radiation mechanisms, different signatures on their light-curves, spectra, pulse profiles and polarisation angles are expected in their broadband electromagnetic emission. We show that these measurements put stringent constraints on the way to describe particle electrodynamics in a rotating neutron star magnetosphere.