THE X-RAY LUMINOSITY OF ROTATION-POWERED NEUTRON-STARS

As a result of recent observations with ROSAT and ASCA the number of r otation-powered pulsars seen at X-ray energies has increased substanti ally. In this paper we review the phenomenology of the observed X-ray emission properties. At present 27 pulsars are detected, representing a wide range of ages (10(3) - 7 x 10(9) yrs), magnetic field strength (10(8) - 10(13) G) and spin periods (1.6 - 530 ms). Despite these disp ersions in parameters all pulsars show an X-ray luminosity closely cor related with the rotational energy loss. This suggests that most of th e observed X-rays are produced by magnetospheric emission originating from the co-rotating magnetosphere. Only for three middle aged pulsars (PSR 0656+14, Geminga and PSR 1055-52) and probably for the Vela-puls ar an additional thermal component is detected which can be attributed to thermal emission from the neutron stellar surface.