2003ApJ...591..361G

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, E{dot}. 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+αE{dot}^–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.