Pulsar Statistics and Demography

3 Pulsar Statistics and Demography

The observed pulsar sample is heavily biased towards the brighter objects that are the easiest to detect. What we observe represents only the tip of the iceberg of a much larger underlying population [132 ]. The bias is well demonstrated by the projection of pulsars onto the Galactic plane shown in Figure 11 . The clustering of sources around the Sun seen in the left panel is clearly at variance with the distribution of other stellar populations which show a radial distribution symmetric about the Galactic centre. Also shown in Figure 11 is the cumulative number of pulsars as a function of the projected distance from the Sun compared to the expected distribution for a simple model population with no selection effects. The observed number distribution becomes strongly deficient beyond a few kpc.

Figure 11: Left panel: The current sample of all known radio pulsars projected onto the Galactic plane. The Galactic centre is at the origin and the Sun is at (0, 8.5) kpc. Note the spiral-arm structure seen in the distribution which is now required by the most recent Galactic electron density model [88

, 89

]. Right panel: Cumulative number of pulsars as a function of projected distance from the Sun. The solid line shows the observed sample while the dotted line shows a model population free from selection effects.

3.1 Selection effects in pulsar searches
  3.1.1 The inverse square law and survey thresholds
  3.1.2 Interstellar pulse dispersion and multipath scattering
  3.1.3 Orbital acceleration
3.2 Correcting the observed pulsar sample
  3.2.1 Scale factor determination
  3.2.2 The small-number bias
  3.2.3 The beaming correction
3.3 The population of normal and millisecond pulsars
  3.3.1 Luminosity distributions and local number estimates
  3.3.2 Galactic population and birth-rates
3.4 The population of relativistic binaries
  3.4.1 Double neutron star binaries
  3.4.2 White dwarf–neutron star binaries
3.5 Going further