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Register a new userThree-dimensional dissipative pulsar magnetospheres with Aristotelian electrodynamics
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A good compromise between the resistive model and the PIC model is Aristotelian electrodynamics, which can include the back-reaction of the radiative photons onto particle motion and allow for a local dissipation where the force-free condition is violated. We study the dissipative pulsar magnetosphere with Aristotelian electrodynamics where particle acceleration is fully balanced by radiation. The expression for the current density is defined by introducing a pair multiplicity. The 3D structure of the pulsar magnetosphere is then presented by solving the time-dependent Maxwell equations using a pseudo-spectral algorithm. It is found that the dissipative magnetosphere approaches the force-free solution and the dissipative region is more restricted to the current sheet outside the light-cylinder (LC) as the pair multiplicity increases. The spatial extension of the dissipative region is self-consistently controlled by the pair multiplicity. Our simulations show the high magnetospheric dissipation outside the LC for the low pair multiplicity.
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The pulsar light curves and energy spectra are explored in dissipative pulsar magnetospheres with the Aristotelian electrodynamics (AE), where particle acceleration is fullly balanced with radiation reaction. The AE magnetospheres with non-zero pair multiplicity are computed by a pseudo-spectral method in the co-moving frame. The dissipative region near the current sheet outside the LC is accurately captured by the high-resolution simulation. The pulsar light curves and spectra are computed by the test particle trajectory method including the influence of both the consistent accelerating electric field and radiation reaction. Our results can generally reproduce the double-peak light curves and the GeV cut-off energy spectra in agreement with the Fermi observations for the pair multiplicity $kappagtrsim1$.
We consider magnetospheric structure of rotating neutron stars with internally twisted axisymmetric magnetic fields. The twist-induced and rotation-induced toroidal magnetic fields align/counter-align in different hemispheres. Using analytical and numerical calculations (with PHAEDRA code) we show that as a result the North-South symmetry is broken: the magnetosphere and the wind become angled, of conical shape. Angling of the magnetosphere affects the spindown (making it smaller for mild twists), makes the return current split unequally at the Y-point, produces anisotropic wind and linear acceleration that may dominate over gravitational acceleration in the Galactic potential and give a total kick up to $sim 100$ km/s. We also consider analytically the structure of the Y-point in the twisted magnetosphere, and provide estimate of the internal twist beyond which no stable solutions exist: over-twisted magnetospheres must produce plasma ejection events.
The SKA will discover tens of thousands of pulsars and provide unprecedented data quality on these, as well as the currently known population, due to its unrivalled sensitivity. Here, we outline the state of the art of our understanding of magnetospheric radio emission from pulsars and how we will use the SKA to solve the open problems in pulsar magnetospheric physics.
We continue our investigation of particle acceleration in the pulsar equatorial current sheet (ECS) that began with Contopoulos (2019) and Contopoulos & Stefanou (2019). Our basic premise has been that the charge carriers in the current sheet originate in the polar caps as electron-positron pairs, and are carried along field lines that enter the equatorial current sheet beyond the magnetospheric Y-point. In this work we investigate further the charge replenishment of the ECS. We discovered that the flow of pairs from the rims of the polar caps cannot supply both the electric charge and the electric current of the ECS. The ECS must contain an extra amount of positronic (or electronic depending on orientation) electric current that originates in the stellar surface and flows outwards along the separatrices. We develop an iterative hybrid approach that self-consistently combines ideal force-free electrodynamics in the bulk of the magnetosphere with particle acceleration along the ECS. We derive analytic approximations for the orbits of the particles, and obtain the structure of the pulsar magnetosphere for various values of the pair-formation multiplicity parameter kappa. For realistic values kappa >> 1, the magnetosphere is practically indistinguishable from the ideal force-free one, and therefore, the calculation of the spectrum of high-energy radiation must be based on analytic approximations for the distribution of the accelerating electric field in the ECS.
The current state of the art in pulsar magnetosphere modeling assumes the force-free limit of magnetospheric plasma. This limit retains only partial information about plasma velocity and neglects plasma inertia and temperature. We carried out time-dependent 3D relativistic magnetohydrodynamic (MHD) simulations of oblique pulsar magnetospheres that improve upon force-free by retaining the full plasma velocity information and capturing plasma heating in strong current layers. We find rather low levels of magnetospheric dissipation, with less than 10% of pulsar spindown energy dissipated within a few light cylinder radii, and the MHD spindown that is consistent with that in force-free. While oblique magnetospheres are qualitatively similar to the rotating split-monopole force-free solution at large radii, we find substantial quantitative differences with the split-monopole, e.g., the luminosity of the pulsar wind is more equatorially concentrated than the split-monopole at high obliquities, and the flow velocity is modified by the emergence of reconnection flow directed into the current sheet.
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