Toward a Realistic Pulsar Magnetosphere

Abstract

We present the magnetic and electric field structures as well as the currents and charge densities of pulsar magnetospheres which do not obey the ideal condition, E · B = 0. Since the acceleration of particles and the production of radiation requires the presence of an electric field component parallel to the magnetic field, E , the structure of non-Ideal pulsar magnetospheres is intimately related to the production of pulsar radiation. Therefore, knowledge of the structure of non-Ideal pulsar magnetospheres is important because their comparison (including models for the production of radiation) with observations will delineate the physics and the parameters underlying the pulsar radiation problem. We implement a variety of prescriptions that support nonzero values for E and explore their effects on the structure of the resulting magnetospheres. We produce families of solutions that span the entire range between the vacuum and the (ideal) Force-Free Electrodynamic solutions. We also compute the amount of dissipation as a fraction of the Poynting flux for pulsars of different angles between the rotation and magnetic axes and conclude that this is at most 20-40% (depending on the non-ideal prescription) in the aligned rotator and 10% in the perpendicular one. We present also the limiting solutions with the property J = ρc and discuss their possible implication on the determination of the "on/off" states of the intermittent pulsars. Finally, we find that solutions with values of J greater than those needed to null E locally produce oscillations, potentially observable in the data.

Pulsar State Switching From Markov Transitions and Stochastic Resonance

“…However, the stochastic resonance model for the quasiperiodicity in B1931+24 suggests the action of a ∼38 day period forcing function that is easiest to understand as modulation of the return current from a region outside the light cylinder. Equatorial current sheets that are disk-like are a common feature in recent numerical simulations of pulsar magnetospheres for aligned rotators (Krause-Polstorff & Michel 1985;Contopoulos 2005;Timokhin 2010;Kalapotharakos et al 2012;Li et al 2012aLi et al , 2012b. Equatorial disks are prominent in charge-starved cases (Michel 1980) that are electromagnetically "dead."…”

“…The potential drop sustains the current flow that contributes to the spin-down torque and, along with secondary particles, produces radio to gamma-ray emission. The OFL region and magnetic PC are defined self-consistently from the combined ambient stellar magnetic field and current-driven field; the latter, in turn, depends on boundary conditions imposed by the global structure of the magnetosphere (e.g., Kalapotharakos et al 2012).…”

“…Recent simulations (Kalapotharakos et al 2012;Li et al 2012aLi et al , 2012b demonstrate exquisitely how the spin-down rate depends on the magnetic flux threading the light cylinder and takes on limiting values for vacuum (ρ = 0) and force-free (ρ = ρ GJ ) conditions in the OFL region. Spin-down rates in these limits differ by a factor of four for inclination angles of 45 • , easily bracketing the 2.5:1 range seen in long-term intermittent pulsars.…”

THE SECOND FERMI LARGE AREA TELESCOPE CATALOG OF GAMMA-RAY PULSARS

“…Modeling its emission drives ever-more sophisticated electrodynamic calculations (e.g., Wang & Hirotani 2011;Li et al 2012;Kalapotharakos et al 2012b;Pétri 2012). Throughout this paper, we will call pulsars in the main population of the spin period (P) and period derivative (Ṗ ) plane "young" to distinguish them from the much older "recycled" pulsars, including MSPs.…”

Gamma-ray pulsars: A gold mine

“…Although the force-free solutions contain the distribution of charges and currents, including current closure, in the magnetosphere, they demand, by definition, that the electric field along the magnetic field direction vanish (ideal MHD). These force-free models can provide the global configuration of the pulsar magnetosphere but can tell us little about particle acceleration and emission.In the last few years, two groups [133,134] have begun developing dissipative pulsar magnetosphere models, where the ideal MHD condition for zero parallel electric field is dropped. These models assume a formulation for Ohm's law relating the macroscopic current to the electric field along magnetic field lines through a macroscopic conductivity parameter.…”