Pulsar radio emission mechanisms: a critique. (arXiv:2006.15243v1 [astro-ph.HE])

Pulsar radio emission mechanisms: a critique. (arXiv:2006.15243v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Melrose_D/0/1/0/all/0/1">D. B. Melrose</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rafat_M/0/1/0/all/0/1">M. Z. Rafat</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mastrano_A/0/1/0/all/0/1">A. Mastrano</a>

We consider critically the three most widely favored pulsar radio emission
mechanisms: coherent curvature emission (CCE), beam-driven relativistic plasma
emission (RPE) and anomalous Doppler emission (ADE). We assume that the pulsar
plasma is one dimensional (1D), streaming outward with a bulk Lorentz factor
$gamma_{rm s} gg langlegammarangle -1 gtrsim 1$, where
$langlegammarangle$ is the intrinsic spread in the rest frame of the plasma.
We argue that the formation of beams in a multi-cloud model is ineffective in
the intrinsically relativistic case for plausible parameters, because the
overtaking takes too long. We argue that the default choice for the particle
distribution in the rest frame is a J{“u}ttner distribution and that
relativistic streaming should be included by applying a Lorentz transformation
to the rest-frame distribution, rather than the widely assumed relativistically
streaming Gaussian distribution. We find that beam-driven wave growth is
severely restricted by (a) the wave properties in pulsar plasma, (b) a
separation condition between beam and background, and (c) the inhomogeneity of
the plasma in the pulsar frame. The growth rate for the kinetic instability is
much smaller and the bandwidth of the growing waves is much larger for a
J{“u}ttner distribution than for a relativistically streaming Gaussian
distribution. No reactive instability occurs at all for a J{“u}ttner
distribution. We conclude that none of CCE, RPE and ADE in tenable as the
generic pulsar radio emission mechanism for “plausible” assumptions about the
pulsar plasma.

We consider critically the three most widely favored pulsar radio emission
mechanisms: coherent curvature emission (CCE), beam-driven relativistic plasma
emission (RPE) and anomalous Doppler emission (ADE). We assume that the pulsar
plasma is one dimensional (1D), streaming outward with a bulk Lorentz factor
$gamma_{rm s} gg langlegammarangle -1 gtrsim 1$, where
$langlegammarangle$ is the intrinsic spread in the rest frame of the plasma.
We argue that the formation of beams in a multi-cloud model is ineffective in
the intrinsically relativistic case for plausible parameters, because the
overtaking takes too long. We argue that the default choice for the particle
distribution in the rest frame is a J{“u}ttner distribution and that
relativistic streaming should be included by applying a Lorentz transformation
to the rest-frame distribution, rather than the widely assumed relativistically
streaming Gaussian distribution. We find that beam-driven wave growth is
severely restricted by (a) the wave properties in pulsar plasma, (b) a
separation condition between beam and background, and (c) the inhomogeneity of
the plasma in the pulsar frame. The growth rate for the kinetic instability is
much smaller and the bandwidth of the growing waves is much larger for a
J{“u}ttner distribution than for a relativistically streaming Gaussian
distribution. No reactive instability occurs at all for a J{“u}ttner
distribution. We conclude that none of CCE, RPE and ADE in tenable as the
generic pulsar radio emission mechanism for “plausible” assumptions about the
pulsar plasma.

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