Gamma-Ray Emission from Pulsars

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Presentation transcript:

Gamma-Ray Emission from Pulsars

The Famous Supernova of 1987: SN 1987A Before At maximum Unusual type II Supernova in the Large Magellanic Cloud in Feb. 1987

The Remnant of SN 1987A Ring due to SN ejecta catching up with pre-SN stellar wind; also observable in X-rays.

Properties of Neutron Stars Typical size: R ~ 10 km Mass: M ~ 1.4 – 3 Msun Density: r ~ 4x1014 g/cm3 → 1 teaspoon full of NS matter has a mass of ~ 2 billion tons!!! Rotation periods: ~ a few ms – a few s Magnetic fields: B ~ 108 – 1015 G (Atoll sources; ms pulsars) (magnetars)

Images of Pulsars and other Neutron Stars The vela Pulsar moving through interstellar space The Crab nebula and pulsar

The Crab Pulsar Remnant of a supernova observed in A.D. 1054 Pulsar wind + jets Remnant of a supernova observed in A.D. 1054

The Crab Pulsar Visual image X-ray image

The Discovery of Pulsars

The Lighthouse Model of Pulsars A Pulsar’s magnetic field has a dipole structure, just like Earth. Radiation is emitted mostly along the magnetic poles. Rapid rotation along axis not aligned with magnetic field axis → Light house model of pulsars Pulses are not perfectly regular → gradual build-up of average pulse profiles

Pulsar periods Over time, pulsars lose energy and angular momentum Over time, pulsars lose energy and angular momentum => Pulsar rotation is gradually slowing down. dP/dt ~ 10-15 Pulsar Glitches: DP/P ~ 10-7 – 10-8

Energy Loss of Pulsars From the gradual spin-down of pulsars: d From the gradual spin-down of pulsars: d dE/dt = (½ I w2) = I w w = - ⅔ m┴2 w4 c-3 dt m┴ ~ B0 r sin a One can estimate the magnetic field of a pulsar as B0 ≈ 3 x 1019 √PP G

Pulsar periods and derivatives Associated with supernova remnants Mostly in binary systems

Pulsar Emission Models Particles can be accelerated to ultrahigh energies in two regions in pulsar magnetospheres: A) Polar Cap Models Particle acceleration along the extremely strong magnetic field lines (close to the surface) near the polar cap Synchrotron emission Curvature radiation Pair production Electromagnetic cascades

Pulsar Emission Models (cont.) B) Outer Gap Models W Particles follow magnetic field lines almost out to the light cylinder => Acceleration to ultrarelativistic energies Synchrotron emission Curvature radiation Pair production Electromagnetic cascades Light Cylinder

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