X‐Ray Spectra of Young Pulsars and Their Wind Nebulae: Dependence on Spin‐Down Energy Loss Rate

An observational model is presented for the spectra of young rotation-powered pulsars and their nebulae based on a study of nine bright Crab-like pulsar systems observed with the Chandra X-ray observatory. A significant correlation is discovered between the X-ray spectra of these pulsars and that of their associated pulsar wind nebulae, both of which are observed to be a function of the spin-down energy loss rate, . The 2-10 keV spectra of these objects are well characterized by an absorbed power-law model with photon indices, Γ, in the range of 0.6 < Γ PSR < 2.1 and 1.3 < Γ PWN < 2.3, for the pulsars and their nebulae, respectively. A linear regression fit relating these two sets of indexes yields Γ PWN = 0.91 ± 0.18 + (0.66 ± 0.11)Γ PSR , with a correlation coefficient of r = 0.97. The spectra of these pulsars are found to steepen as Γ = Γ max + α -1/2 , with Γ max providing an observational limit on the spectral slopes of young rotation-powered pulsars. These results reveal basic properties of young pulsar systems, allow new observational constraints on models of pulsar wind emission, and provide a means of predicting the energetics of pulsars lacking detected pulsations.