Pulsar Theory

1
Pulsar Theory

• Goldreich and Julian 1969
• Ruderman and Sutherland 1975
• Dan
• Fabrycky
• AST 541
• 9/27/04

2
Historical Context
From Pulsar Astronomy, 1998 by Lyne and
Graham-Smith

• 1934 Baade and Zwicky propose neutron stars
• 1968 Pulsars discovered in radio by Hewish et al.
• Pacini and Gold pulsars neutron stars
• 1969 Crab Pulsar period slows, pulsesgtrotation
• Polarization rotates during pulse

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Electromagnetism warm-up
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Goldreich Julian 1969

• Title Pulsar Electrodynamics
• Main Points
• Model neutron star spin and magnetic axes
  aligned
• A magnetosphere must surround it
• All regions have non-zero net charge
• Magnetic torque slows the rotation
• Variations in star create variations in the nebula

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Magnetosphere existence

• Interior is conductor charges rearrange until
• If exterior is vacuum

gt FEM / Fgrav 5 108 for protons, 8 1011 for
electrons
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Near Zone
NS supplies charges to maintain This leads to a
co-rotating magnetosphere with charge density
Remarkably, charges are mostly separated!
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Wind Zone

• Beyond a cylindrical radius magnetic
  field lines dont close until supernovae shell
• p/e regions separate-- charges slide along B
  lines.
• Escaping charges induce a toriodal B, which comes
  to dominate the inner dipole

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Magnetic Torque Slow-Down

• Integrating Maxwells stress-tensor over sphere
• It slows down with
• gt

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Boundary Zone

• B lines no longer equipotentials
• Particles accelerated to relativistic energies
• Charges mix throughout

Potential fall
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Chandra/HST Crab movie
Deleted to conserve space. Please watch it
at http//chandra.harvard.edu/photo/2002/0052/mov
ies.html
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Citations to GJ

• Existence of Pulsar Wind Nebulae
• Concept of light-cylinder, corotating
  magnetosphere
• Simplest case nearly all models start here
• Charge density equation

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Ruderman Sutherland (1975)
Title Theory of Pulsars Polar Gaps, Sparks,
and Coherent Microwave Radiation

• Premise
• Pulsars are NS with magnetic and rotation axes
  anti-aligned (anti-pulsars have them aligned)
• Poles positive, equator negative

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Ions bound to surface?

• Molecular chains of iron and other ions
• E0 14 keV / (eZ d) 1012V/cm Emax1011/P
  V/cm
• (eZ is ion charge, d10-9cm is spacing)
• To boil them off, T6 106, X-ray flux 1038erg/s
• Not observed.
• Bombardment with relativistic particles?
• Emax1 keV, independent of energy compare 14
  keV.
• Ions stay put.

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Polar Gaps
No charges in region gt Gap Polar region rotates
slower
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Sparks
2mec gamma-rays seed pair production Curvature
radiation Into an angle Avalanche requires
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Drifting sub-pulses
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Spark Carousel within the Lighthouse
Kirchoffs Law
ab on gap boundary bf just below surface
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Observational cones
Polarization sweeps during sub-pulse
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Radiation Coherency
Bunching mode in e-/e plasma causes coherent
radiation. Only works below plasma frequency
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Citations to RS

• Strengths
• Sub-pulse drift mechanism
• Correctly quantified P3
• Lovely diagrams
• Weaknesses
• Ion binding energy possibly surmountable
• Probably doesnt work for anti-pulsars
• Ahh- complicated assumptions discussed ad nausea
  lots of citations!