Pulsars (3) ...
Although the Crab Pulsar emits visible light (and X-rays and gamma rays),
most pulsars are detectable only by
their radio frequency
radiation. However, a few emit strongly in other wavelength bands.
Gamma Ray Pulsars
At least three pulsars
are strong sources of gamma rays. The following figure
is an all-sky map in galactic coordinates of gamma-ray intensity in the 1-3 MeV
(million electron-Volt) range, as obtained by the COMPTEL instrument on the orbiting Compton Gamma
Ray Observatory.
Several strong gamma-ray
sources in the galactic plane (the horizontal line through the center)
are marked, including the Crab and Vela Pulsars,
the galactic center
(which may contain a supermassive black hole), and the black hole binary system
Cygnus X-1. Sources above and below the
plane of the galaxy are mostly extragalactic gamma sources
like quasars that we shall discuss in the chapter on quasars and active galaxies.
