Wave dispersion in pulsar plasma. Part 2. Pulsar frame

Rafat, M. Z.; Melrose, D. B.; Mastrano, Alpha

doi:10.1017/s0022377819000448

Cited by 16 publications

(70 citation statements)

References 22 publications

(47 reference statements)

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“…This is one of the main differences from the works of Rafat, Melrose & Mastrano (2019 a ) and Rafat et al. (2019 b ), who analysed the dispersion properties of subluminal waves for arbitrary Lorentz factor of the wave phase velocity . The authors showed that there is a sufficiently large range of values of , in which there is a good agreement with the results of Beskin et al.…”

Section: Description Of the Problemmentioning

confidence: 74%

“…1988, (2.17) 1 ; Rafat et al. 2019 b , (6.17)) On the other hand, for we have (see below). Indeed, for low number density (when ), i.e.…”

Section: Description Of the Problemmentioning

confidence: 85%

“…Rafat et al. 2019 a , b ). As will be shown below, these conditions are not realized in the region of radiation generation.…”

Section: Description Of the Problemmentioning

confidence: 98%

“…But another convention is to interpret as an additional mode any positive-frequency, forward-propagating solution in the pulsar rest frame which arises by a Lorentz transforming of a negative frequency or backward-propagating solution in a plasma reference frame. Below we use the second convention, which, after the work by Rafat, Melrose & Mastrano (2019 b ) and especially after Melrose, Rafat & Mastrano 2020 (see their text after (19)), should no longer raise objections.…”

Section: Introductionmentioning

confidence: 99%

“…On the other hand, Rafat et al. (2019 b ) posed another important problem related to this issue. The point is that in the work by Beskin et al.…”

Section: Introductionmentioning

confidence: 99%

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On the thermal effects on radio waves propagating in the pulsar magnetosphere

2021

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Thermal effects on the properties of four electromagnetic waves propagating in the pulsar magnetosphere are analysed. It is shown that thermal effects change only quantitatively the dispersion properties of superluminal ordinary O-mode freely escaping the pulsar magnetosphere; whereas properties of the extraordinary X-mode remain unchanged. The research shows that for two subluminal waves propagating along magnetic field lines thermal effects result in essential absorption. However, this attenuation occurs at considerable distances from the neutron star, and there is no doubt of their existence.

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Section: Description Of the Problemmentioning

confidence: 74%

“…1988, (2.17) 1 ; Rafat et al. 2019 b , (6.17)) On the other hand, for we have (see below). Indeed, for low number density (when ), i.e.…”

Section: Description Of the Problemmentioning

confidence: 85%

“…Rafat et al. 2019 a , b ). As will be shown below, these conditions are not realized in the region of radiation generation.…”

Section: Description Of the Problemmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

“…On the other hand, Rafat et al. (2019 b ) posed another important problem related to this issue. The point is that in the work by Beskin et al.…”

Section: Introductionmentioning

confidence: 99%

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On the thermal effects on radio waves propagating in the pulsar magnetosphere

2021

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Wave dispersion in pulsar plasma. Part 1. Plasma rest frame

2019

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Wave dispersion in a pulsar plasma (a 1D, strongly magnetized, pair plasma streaming highly relativistically with a large spread in Lorentz factors in its rest frame) is discussed, motivated by interest in beam-driven wave turbulence and the pulsar radio emission mechanism. In the rest frame of the pulsar plasma there are three wave modes in the lowfrequency, non-gyrotropic approximation. For parallel propagation (wave angle θ = 0) these are referred to as the X, A and L modes, with the X and A modes having dispersion relation |z| = z A ≈ 1 − 1/2β 2 A , where z = ω/k c is the phase speed and β A c is the Alfvén speed. The L mode dispersion relation is determined by a relativistic plasma dispersion function, z 2 W (z), which is negative for |z| < z 0 and has a sharp maximum at |z| = z m , with 1 − z m < 1 − z 0 ≪ 1. We give numerical estimates for the maximum of z 2 W (z) and for z m and z 0 for a 1D Jüttner distribution. The L and A modes reconnect, for z A > z 0 , to form the O and Alfvén modes for oblique propagation (θ = 0). For z A < z 0 the Alfvén and O mode curves reconnect forming a new mode that exists only for tan 2 θ z 2 0 − z 2 A . The L mode is the nearest counterpart to Langmuir waves in a nonrelativistic plasma, but we argue that there are no "Langmuir-like" waves in pulsar plasma, identifying three features of the L mode (dispersion relation, ratio of electric to total energy and group speed) that are not Langmuir-like. A beam-driven instability requires a beam speed equal to the phase speed of the wave. This resonance condition can be satisfied for the O mode, but only for an implausibly energetic beam and only for a tiny range of angles for the O mode around θ ≈ 0. The resonance is also possible for the Alfvén mode but only near a turnover frequency that has no counterpart for Alfvén waves in a nonrelativistic plasma.

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Wave dispersion in pulsar plasma. Part 3. Beam-driven instabilities

2019

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Beam-driven instabilities are considered in a pulsar plasma assuming that both the background plasma and the beam are relativistic Jüttner distributions. In the rest frame of the background, the only waves that can satisfy the resonance condition are in a tiny range of slightly subluminal phase speeds. The growth rate for the kinetic (or maser) version of the weak-beam instability is much smaller than has been estimated for a relativistically streaming Gaussian distribution, and the reasons for this are discussed. The growth rate for the reactive version of the weak-beam instability is treated in a conventional way. We compare the results with exact calculations, and find that the approximate solutions are not consistent with the exact results. We conclude that, for plausible parameters, there is no reactive version of the instability. The growth rate in the pulsar frame is smaller than that in the rest frame of the background plasma by a factor 2γ s , where γ s = 10 2 −10 3 is the Lorentz factor of the bulk motion of the background plasma, placing a further constraint on effective wave growth. Based on these results, we argue that beam-driven wave growth probably plays no role in pulsar radio emission.

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Wave dispersion in pulsar plasma. Part 2. Pulsar frame

Cited by 16 publications

References 22 publications

On the thermal effects on radio waves propagating in the pulsar magnetosphere

On the thermal effects on radio waves propagating in the pulsar magnetosphere

Wave dispersion in pulsar plasma. Part 1. Plasma rest frame

Wave dispersion in pulsar plasma. Part 3. Beam-driven instabilities

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