Mon. Not. R. Astron. Soc., 485, 5319-5328 (2019/June-1)
On X-ray emission of radio pulsars.
MALOV I.F. and TIMIRKEEVA M.A.
Abstract (from CDS):
An analysis of distributions of some parameters of radio pulsars emitting X-ray radiation was carried out. The majority of such pulsars have short spin periods with mean value <P> = 133 msec. The distribution of period derivatives reveals a bimodality. One of the groups contains millisecond (recycled) pulsars with < logd/P dt> = -19.69. Pulsars with long periods and < logd/P dt> = -13.61 belong to the second group. Magnetic fields at the surface of the neutron star are characterized by a bimodal distribution as well. The mean values of <log Bs> are 8.48 and 12.41, respectively, for the mentioned groups. The distribution of magnetic fields near the light cylinder does not show noticeable bimodality. The median value of logB_ lc_=4.43 is almost three orders of magnitude higher compared with that for radio pulsars without a registered X-ray emission (<log Blc> = 1.75). The median value of the loss of rotational energy (< logd/E dt> = 35.24) is also three orders of magnitude higher than the corresponding value for X-ray quiet radio pulsars. There is the expected strong correlation (the correlation coefficient is 0.97) between X-ray luminosity and loss of rotational energy, which are believed to be the main sources of all processes in pulsar magnetospheres. Dependence of X-ray luminosity on the magnetic field at the light cylinder has been detected. It supports the hypothesis that generation of non-thermal X-ray emission takes place at the periphery of the magnetosphere and is caused by the synchrotron mechanism. We detected positive correlations between luminosities in X-ray and gamma-ray ranges. Our results show that a purposeful search for pulsars in the hard electromagnetic ranges can be carried out for radio pulsars with high values of d/E dt and Blc.