High energy radiation from various classes of galactic and extragalactic objects has been observed for nearly 30 years. A large fraction of galactic sources is associated with neutron-stars: rotation powered pulsars, accretion powered pulsars and so on. Neutron stars are very small by astronomical standards. Our own Sun's radius is 100 times bigger than the radius of the Earth. However, the typical radius of a neutron star is thought to be only about 10 kilometers (6.25 miles). At the same time, a neutron star contains up to 1.5 times as much matter as the Sun, making the density of these objects tremendous. A teaspoon of neutron star material weighs about a billion (1,000,000,000) tons. This much matter in such a small space creates an enormous gravitational field, so powerful, in fact, that it can bend light!
Pulsars are highly magnetized rapidly spinning stars schematically shown in FIG. 8. The strength of magnetic field is estimated by the assumption that the rotation energy of the neutron star powers the radiation originally via the magnetic dipole radiation. The rotation energy of a neutron star of inertia moment rotating with angular velocity and its time derivative read
Detection of radio, X-ray, and -rays from pulsars has indicated that high energy radiation takes places in pulsar magnetosphere. Process relevant for production and transfer of high energy radiation in a pulsar are:
Electrons are thought to be accelerated to relativistic energies and very high energy (VHE) -rays are produced via curvature radiation. Generated photons pair-produce pairs by either magnetic pair creation (such as Crab Pulsar) or photon-photon pair creation (like Vela pulsar). These secondary electrons are subject to the synchrotron radiation.
Now we can estimate the energy of -rays radiated by the accelerated electrons in the magnetosphere. Equation 47 gives the typical photon energy of synchrotron photons in the magnetosphere of Gauss. Using rad/sec/Gauss, MeV s and that keV, we obtain