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

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Presentation transcript:

Pulsars Basic Properties

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

What is a Neutron Star ?

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

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

Discovery of Pulsars in Radioastronomy PSR T = 1.33 s Where is the radiation coming from?

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

The Braking Index magnetic braking predicts: braking index n measurable via: Crab:n = ± PSR :n = 2.8 ± 0.2 PSR :n = 2.01 ± 0.02 not bad...but other braking mechanisms seem to be active in addition!

Magnetic Field at Surface Crab Pulsar: R

The Age of a Pulsar 10 8 T 10 6 T 10 6 yr yr T (s) log 10 T · decay of B S with τ = 10 7 yr

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

Rotating Pulsar = Unipolar Inductor E ind surface forces 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

T (s) log 10 T · Limit for Coherent Radio Emission e + e – death line theory for coherent emission from e + e – cascades along pole field lines => (M.A. Ruderman, P.G.Sutherland: Astrophys. J. 196 (1975) 51.)

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

Open Magnetic Field Lines toroidal field outside light cylinder dragged by outflowing plasma equatorial neutral current sheet for misaligned pulsar STAR

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) log 10 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: rMrM

log ( T (L/10 30 W) 6/7 ) log ( -T / T ) · Spin-Up Phase angular momentum transfer from disk onto pulsar (friction at r M ): end of spin-up at Ω = Ω Kepler (r M ): M = M R = 10 km L = L E

T (s) log 10 T · Spin-Up Limit spin-down due to magnetic dipole radiation limited by spin-up (T min ): spin-up limit fulfilled for all ms-binaries but not at all for normal pulsars (as expected)!!

Summary models for pulsars and X-ray binaries pretty successful open problem: gamma ray emission from pulsars ? open problem: which processes contribute to gamma ray emission from surrounding SNRs ?