2.2 Pulse Profiles2 The Pulsar Phenomenon2 The Pulsar Phenomenon

2.1 The lighthouse model

The so-called ``lighthouse model'' used to explain the basic pulsar phenomenon is demonstrated in the animated image shown in Fig.  1 . As the neutron star spins, charged particles are accelerated out along magnetic field lines in the magnetosphere (depicted by the light blue cones). This acceleration causes the particles to emit electromagnetic radiation, most readily detected at radio frequencies as a sequence of observed pulses produced as the magnetic axis (and hence the radiation beam) crosses the observer's line of sight each rotation. The period of the pulses is simply the rotation period of the neutron star. The position of the tracker ball on the idealised pulse profile in the animation shows precisely the relationship between observed intensity and rotational phase of the neutron star.

  

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Figure 1: The rotating neutron star (or ``lighthouse'') model for pulsar emission. Click here to see the movie in action. Animation designed by Michael Kramer.

Neutron stars are extremely stable rotators. They are essentially equivalent to large celestial flywheels with moments of inertia tex2html_wrap_inline1838 tex2html_wrap_inline1840 . The rotating neutron star model, which was independently developed by Pacini and Gold in 1968 [121, 65] correctly predicts that the pulse period should gradually increase as the outgoing radiation carries away rotational kinetic energy. When a period increase of 36.5 ns per day was measured for the pulsar in the Crab nebula [130], Gold showed that a rotating neutron star with a large magnetic field must be the dominant energy supply to the nebula and the model became universally accepted.



2.2 Pulse Profiles2 The Pulsar Phenomenon2 The Pulsar Phenomenon

image Binary and Millisecond Pulsars
D. R. Lorimer (dunc@mpifr-bonn.mpg.de)
http://www.livingreviews.org/lrr-1998-10
© Max-Planck-Gesellschaft. ISSN 1433-8351
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