Basic Properties By Dr. Lohse, University of Berlin

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Presentation transcript:

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

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

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

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

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

not bad...but other braking mechanisms seem to be active in addition! 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!

Magnetic Field at Surface Crab Pulsar:

The Age of a Pulsar · log10 T decay of BS with τ = 107 yr T (s) 108 T

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

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

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 => T (s) log10 T · e+e– death line

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

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

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

Magnetosphere Charge Density general case

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

Pulse Patterns up to Egret Energies

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

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: Alvén radius: rM

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

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