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 . The
extent to which the sample is incomplete is well demonstrated by the projection of pulsars onto the Galactic
plane and their cumulative number distribution as a function of distance shown in Figure 11. The
clustering of sources around the Sun seen in the left panel of Figure 11 is clearly at variance with the
distribution of other stellar populations which show a radial distribution about the Galactic
The extent to which the pulsar sample is incomplete can be seen from the cumulative number
of pulsars as a function of the projected distance from the Sun. In Figure 11 the observed
distribution is compared to the expected distribution for a simple model population with no
selection effects. The observed number distribution becomes strongly deficient beyond a few
||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 . Note the spiral-arm
structure seen in the distribution which is now required by the electron density model [73, 74]. 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.