Neutron star concluded that the radiation comes from a neutron star at the stage of accretion. In 1967, Jocelyn Bell Burnell and Antony Hewish discovered regular radio pulses from PSR B1919+21. This pulsar was later interpreted as an isolated, rotating neutron star. The energy source of the pulsar is the rotational energy of the neutron star. The majority of known neutron stars (about 2000, as of 2010) have been discovered as pulsars, emitting regular radio pulses. In 1971, Riccardo Giacconi, Herbert Gursky, Ed Kellogg, R. Levinson, E. Schreier, and H. Tananbaum discovered 4.8 second pulsations in an X-ray source in the constellation
Fan-beam antenna latter send back in space a highly focused parallel beam that one can describe as pencil shape. When one removes a section of the paraboloid, rays coming from that section are lost. In keeping the antenna only in the horizontal or the vertical, only the rays at right angle to the remaining antenna section will be focused and thus create a narrow beam in that direction while being wide in the other direction. Fan beam antennas are used in radar sets. Primary radar in airport have often fan-beam with the section of antenna oriented horizontally to give a narrow beam