A multicomponent Langmuir-mode source for the observed pulsar coherent emission

Abstract

Several classes of neutron star are sources of coherent emission at frequencies of 10 2 − 10 3 MHz: others are radio-quiet. The primary emission spectra are broadly universal in form over many orders of magnitude in rotation period and polar-cap magnetic flux density. The existence of nulls and mode-changes in some radio-loud pulsars can be understood only as a manifestation of magnetospheric bistability. An ion-proton plasma with a possible background of electron-positron pairs is formed at the polar caps of stars with positive corotational charge density and is shown here to be a physical basis for the presence or absence of coherent emission and a likely reason why bistability may be present in the later stages of a pulsar lifetime.

Circular polarization shows the nature of pulsar magnetosphere composition

“…Sections 1 -3 have attempted to set out those features of the ion-proton plasma that lead to coherent linearly-polarized radio-frequency emission. Langmuir-mode growth rates are such that non-linearity and a transition to turbulence can occur at altitudes in the interval 2 < η < 10 above the polar cap (see Jones 2012Jones , 2015. Following this, it has been argued that turbulent development and coherent emission occur at low altitudes and in intervals at least as compact as those favoured by observation.…”

“…In the observer frame, the emitting region moves a distance less than of the order of 10 −5 γc ≈ 3 × 10 6 cm for an ion Lorentz factor γ = 10. We refer to Jones (2015) and papers cited therein giving the reasons for this order of Lorentz factor. This distance is by no means inconsistent with the compact emission volumes quoted by Hassall et al (2012) and by Kramer et al (1999) for MSP, or with the requirement for efficient generation of radio-frequency power mentioned in the previous paragraph.…”

“…The possibility of a small secondary electron-positron component being present in the ion-proton plasma was considered at length in Jones (2015) owing to its effect on the rate of growth of Langmuir modes. Positrons accelerated to energies of 10 4−5 Mev are not significant in this respect: their Lorentz factors are too great for them to participate other than negligibly in collective plasma modes.…”

A bistable pulsar magnetosphere: nulls and mode changes

“…However, in the case of very high fields (> Bc) low energy electron-positron pairs may be present and the Langmuir-mode dispersion relation so modified that growth is prevented. We refer to Jones (2015) for details of this additional explanation for nulls.…”

Polar caps in the presence of an induction field

“…The properties of the mode do not otherwise depend on the polar magnetic field and so differ little over a wide range of objects, from normal pulsars to millisecond pulsars (MSP) and are consistent with the almost universal spectral properties of the radio emission. We refer to Jones (2015) and papers cited therein for further details of the case for Ω · B < 0 pulsars. Possible observable consequences of plasma drift in the corotating frame for the Ω · B > 0 case are considered briefly in Section 6.…”