Coherent Emission Mechanisms

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Coherent Emission Mechanisms

• Roger Blandford
• KIPAC
• Stanford

2
Why do we care?

• The whistle on the locomotive
• We only need to know why pulsars pulse, not how
  they shine
• Alternatively,
• Related to studies of powerful g-ray emission
• Important sometimes when pulsars are tools
• Accurate timing eg geodetic precession
• Scintillation experiments
• Best laboratory for relativistic plasma physics
• New light sources
• Microwave generators
• Genuinely interesting physics and very good data!

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Radio Pulses

• Core cone structure (Rankin)
• Open flux boundary layer/slot gap/return current
• Linear, circular polarization swings
• Propagation, orthogonal mode transitions
• Millistructure
• Subpulse drift
• Microstructure
• TB 1030 K
• Nanostructure
• dn 0.1n
• Location?
• H500km in Vela?

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Magnetosphere

• GJ density shorts out E
• Must replenish charge on open flux tube also
  closed flux!
• Polar gap (Sturrock, Ruderman Sutherland)
• TeV primary positrons create curvature g-rays if
  W.Bgt0
• Create 100MeV pairs on field
• n104 nGJ?? - Wind need much more plasma?
• Anti-pulsars? Ions?
• Outer gap/slot gap? (Holloway, Arons)
• Currents and charges modify magnetosphere
• TeVltltPeV so force-free probably OK (Spitkovsky)
• Differential rotation along field?
• Streaming may be necessary to dissipate
• Primary beam? j2-r2gt0?, reverse current?

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General emission mechanisms(cf Goldreich, Pacini
Rees 1972, 1973)

• Antenna mechanisms
• Bunched curvature radiation ng3c/R, kTBltNgmc2
• Lateral coherence?? Frequency structure?
  (Melrose)
• Orthogonal polarization?
• Radiation reaction instability? (Goldreich
  Keeley)
• Plasma turbulence
• Electrostatic turbulence, solitons, nltltnGJ?
• Simulations (Weatherall)
• Attenuation, conversion to EM mode?
• Maser mechanisms

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(Anomalous) Cyclotron Resonance

• Strong absorption in outer magnetosphere?
• Cooling length 0.1 g B12-2 m gtground state
• En ( m2c4 pz2c2 2 h ?Gmc2)1/2
• s2p2recd(w-wG)
• Anomalous Cyclotron Resonance
• Kazbegi, Machabeli, Melikhidze Lyutikov
• ????kz vz - s?G / ?
• Let n ck/??gt1
• Can get stimulated emission out of ground state
  if enough parallel momentum is lost by particle
• Kinetic instability for primary electrons (if
  survive)
• cf cosmic ray streaming instability

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Particle distribution function
10
107
104

• Requires specific distribution function
• and location
• O, X-modes excited in outer
• magnetosphere only
• Linearly polarized
• A-modes excited somewhat closer to
• star but have to mode-convert

Dispersion relation in cold pair plasma
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Cerenkov Drift Instability

• Beam/tail particles have curvature drift
• ud g c2 /wG R
• ????kz vz kx ud
• Hydrodynamical instability involving bulk plasma
• Orthogonal polarization to Rotating Vector Model
• Outer magnetosphere
• Saturation
• Quasilinear diffusion
• Stimulated Raman, Induced
• Compton scatttering
• Machabeli, Melikhidze Lyutikov

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Emission Sites
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Phenomenology

• ACR, CDI gt core, cone (Lyuitkov et al)
• Only in the outer magnetosphere r n-1/6
• Not for MSP, young pulsars?
• Frequency structure, CDI orthogonal polarization

Hankins
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Challenges

• Use multi-wavelength studies to describe
  magnetospheric anatomy
• Locate radio emission cite
• MSPs rLC 7RNS!
• Giant pulses (ms), RRATS
• Global magnetospheric simulations
• Study and simulate nanostructure
• Individual emitting elements (c1ft/ns!)
• High energy density physics experiments
• New light sources can make pair plasmas scaled
  experiments
• Relativistic plasma simulations
• Major challenge to capture dynamic range