; Lu, Fang-Jun] Chinese Acad Sci, Lab Particle Astrophys, Inst High Energy Phys, Beijing 100049, Peoples R China
; [Li, Xiang-Hua] Max Planck Inst Radioastron, Hugel 69, D-53121 Bonn, Germany
; [Li, Zhuo] Weizmann Inst Sci, Fac Phys, IL-76100 Rehovot, Israel
; [Li, Zhuo] Peking Univ, Dept Astron, Beijing 100871, Peoples R China
We present a statistical study of the nonthermal X-ray emission of 27 young rotation-powered pulsars (RPPs) and 24 pulsar wind nebulae (PWNe) using the Chandra and XMM-Newton observations, whose high spatial resolutions enable us to resolve pulsars from their surrounding PWNe. We obtain the X-ray luminosities and spectra separately for RPPs and PWNe, and then investigate their distribution and relation to each other, as well as their relation to the pulsar rotational parameters. In pair-correlation analysis we find that (1) the X-ray (2-10 keV) luminosities of both pulsar and PWN (L-X,L- psr and L-X,L- pwn) display a strong correlation with the pulsar spin-down power. (E) over circle and characteristic age tau. The scalings resulting from a simple linear fit to the data are L-X,L- psr alpha (E) over circle (0.92 +/- 0.04) and L-X. pwn alpha (E) over circle (1.45 +/- 0.08) (68% confidence level), respectively; however, neither fit is statistically acceptable. (2) L-X,L- psr also shows a possible weak correlation with the pulsar period P and period derivative. (P) over circle, whereas L-X,L- pwn manifests a similar weak correlation with (P) over circle only. (3) The PWN photon index Gamma(pwn) is positively correlated with L-X,L- pwn and L-X,L- pwn/(E) over circle. We also found that the PWN X-ray luminosity is typically 1 to 10 times larger than that from the underlying pulsar, and the PWN photon indices span a range of 1.5 less than or similar to Gamma(pwn) less than or similar to 2.1. The statistical study of PWN spectral properties supports a particle wind model in which the X-ray emitting electrons are accelerated by the termination shock of the wind.