On X-ray emission of radio pulsars

The analysis of distributions of some parameters of radio pulsars emitting X-ray radiation was carried out. The majority of such pulsars has short spin periods with the average value $< P >$ = 133 msec. The distribution of period derivatives reveals a bimodality, dividing millisecond ($< log \dfrac{dP}{dt}>$ = -19.69) and normal ($< log \dfrac{dP}{dt}>$ = -13.29) pulsars. Magnetic fields at the surface of the neutron star are characterized by the bimodal distribution as well. The mean values of $<log B_s>$ are $8.48$ and $12.41$ for millisecond pulsars and normal ones, respectively. The distribution of magnetic fields near the light cylinder, it does not show the noticeable bimodality. The median value of $log B_{lc}$ = 4.43 is almost three orders higher comparing with this quantity ($<log B_{lc}>$ = 1.75) for radio pulsars without registered X-ray emission. Losses of rotational energy ($<log \dfrac{dE}{dt}>$ = 35.24) are also three orders higher than corresponding values for normal pulsars. There is the strong correlation between X-ray luminosities and losses of rotational energies. The dependence of the X-ray luminosity on the magnetic field at the light cylinder has been detected. It shows that the generation of the non-thermal X-ray emission takes place at the periphery of the magnetosphere and is caused by the synchrotron mechanism. We detected the positive correlations between luminosities in radio, X-ray and gamma -ray ranges. Such correlations give the possibility to carry out a purposeful search for pulsars in one of these ranges if they radiate in other one.