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Pulsars

Pulsars. Basic Properties By Dr. Lohse, University of Berlin. part of angular momentum carried away by shell. field lines frozen into solar plasma. Supernova Explosion => Neutron Stars. (surface field). ” Normal“ Pulsars T > 20 ms. Millisecond Pulsars 1 ms < T < 20 ms.

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Pulsars

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  1. Pulsars Basic Properties By Dr. Lohse, University of Berlin

  2. part of angular momentum carried away by shell field lines frozen into solar plasma Supernova Explosion => Neutron Stars (surface field)

  3. ”Normal“ Pulsars T > 20 ms Millisecond Pulsars 1 ms < T < 20 ms Pulsar Statistics => 2 basic groups number log( T / s ) Crab: T = 33 ms Vela: T = 89 ms

  4. Why T > 1 ms ? virial theorem centrifugal forces would disrupt neutron star if rotating faster!

  5. Pulsars as Magnetic Dipole Antennas misaligned magnetic rotator model magnetic braking by emission of polarized magnetic dipole radiation:

  6. The Braking Index magnetic braking predicts: braking index n measurable via: • Crab: n = 2.515 ± 0.005 • PSR 1509-58: n = 2.8 ± 0.2 • PSR 0540-69: n = 2.01 ± 0.02 not bad...but other braking mechanisms seem to be active in addition!

  7. R Crab Pulsar: Magnetic Field at Surface

  8. · log10 T 108 T 106 yr 106 T 1010 yr decay of BSwith τ = 107 yr T (s) The Age of a Pulsar

  9. explosion observed in 1054 => pulsar properties today: T = 33 ms prediction: Example: Crab Pulsar Not too bad !!

  10. Rotating Pulsar = Unipolar Inductor • Eind surface forces 1012 times stronger than gravity (Crab) • charge particles (electrons...) dragged off surface and accelerated to large energies => • pulsar wind (power source for plerions) • coherent radio emission from e+e–-cascades in B-field at poles

  11. · log10 T T (s) Limit for Coherent Radio Emission (M.A. Ruderman, P.G.Sutherland: Astrophys. J.196 (1975) 51.) theory for coherent emission from e+e– cascades along pole field lines => e+e– death line

  12. magnetosphere:plasma moves along rigid field lines The Pulsar Magnetosphere Crab in X rays

  13. The Pulsar Magnetosphere rigid body approximation breaks down at light cylinder:

  14. Magnetosphere Charge Density (P. Goldreich, W.H.Julian: Astrophys. J.157 (1969) 839.) ignore currents

  15. general case Magnetosphere Charge Density

  16. The Origin of X and γ Radiation • vacuum gap acceleration of e± at • polar cap ?? • outer gap ?? • other models (J.Kirk et al.) ?? • differentiate by observation • X/γ vs. radio pulse pattern • shape of high energy cut-off

  17. Pulse Patterns up to Egret Energies

  18. · log10 T T (s) • What are Millisecond Pulsars? mostly binary systems! very bright X-ray sources close to Eddington luminosity => accretion!!

  19. Alvén radius: Accretion in Strong B-Fields giant star feeds accretion disk around neutron star accretion disk dynamics: orbits with slowly decreasing Kepler radii until plasma magnetically dominated: rM

  20. · log ( -T / T ) M = M R = 10 km L = LE • log ( T (L/1030W)6/7 ) Spin-Up Phase angular momentum transfer from disk onto pulsar (friction at rM ): end of spin-up at Ω = ΩKepler(rM):

  21. · log10 T T (s) Spin-Up Limit spin-down due to magnetic dipole radiation limited by spin-up (Tmin): spin-up limit fulfilled for all ms-binaries but not at all for normal pulsars (as expected)!!

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