Abstract
ABSTRACT The mechanism by which the radiation received from obliquely rotating neutron stars is generated remains an open question half a century after the discovery of pulsars. In contrast, considerable progress has recently been made in determining the structure of the magnetosphere that surrounds these objects: numerical computations based on the force-free, magnetohydrodynamic, and particle-in-cell formalisms have now firmly established that the magnetosphere of an oblique rotator entails a current sheet outside its light cylinder whose rotating distribution pattern moves with linear speeds exceeding the speed of light in vacuum. However, the role played by the superluminal motion of this current sheet in generating the multiwavelength, focused pulses of radiation that we receive from neutron stars is unknown. Here, we insert the description of the current sheet provided by the numerical simulations in the classical expression for the retarded potential and thereby calculate the radiation field generated by this source in the time domain. We find a radiation consisting of highly focused pulses whose salient features (brightness temperature, polarization, spectrum and profile with microstructure and with a phase lag between the radio and gamma-ray peaks) are strikingly similar to those of the emission received from pulsars. In addition, the flux density of this radiation diminishes with the distance D from the star as D−3/2 (rather than D−2) in certain latitudinal directions: a result that suggests that the high energetic requirements normally attributed to magnetars and the sources of fast radio bursts and gamma-ray bursts could be artefacts of the assumption that the radiation fields of all sources necessarily decay as predicted by the inverse-square law.
Highlights
The mechanism by which the radiation received from obliquely rotating neutron stars is generated remains an open question half a century after the discovery of pulsars.1, 2 In contrast, considerable progress has recently been made in determining the structure of the magnetosphere that surrounds these objects: numerical computations based on the force-free, magnetohydrodynamic and particle-in-cell formalisms have firmly established that the magnetosphere of an oblique rotator entails a current sheet outside its light cylinder whose rotating distribution pattern moves with linear speeds exceeding the speed of light in vacuum.3–6 the role played by the superluminal motion of this current sheet in generating the multi-wavelength focused pulses of radiation that we receive from neutron stars is unknown
The only role we assign to the rest of the magnetosphere, whose radiation field is negligibly weaker than that of the current sheet, is to maintain the propagation of this sheet
The multi-wavelength focused pulses emitted by the current sheet escape the plasma surrounding the neutron star in the same way that the radiation generated by the accelerating charged particles invoked in most current attempts at modelling the emission mechanism of these objects does
Summary
The results reported below are consequences mainly of the shape and motion of the current sheet: two features of the magnetosphere which are the same both for a dipolar and a monopolar magnetic field at the surface of the star, and both close to and far from the light cylinder.
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