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-poweredpulsars and their nebulae based on a study of nine bright Crab-like pulsarsystems observed with the Chandra X-ray observatory. A significant correlationis discovered between the X-ray spectra of these pulsars (PSRs) and that oftheir associated pulsar wind nebulae (PWNe), both of which are observed to be afunction of the spin down energy, Edot . The 2 - 10 keV spectra of theseobjects are well characterized by an absorbed power-law model with photonindices, Gamma, in the range of 0.6 < Gamma_PSR < 2.1 and 1.3 < Gamma_PWN <2.3, for the pulsars and their nebulae, respectively. A linear regression fitrelating these two sets of indexes yields, Gamma_PWN = 0.86 +/- 0.20 + (0.72+/- 0.13) X Gamma_PSR, with a correlation coefficient of r = 0.96. The spectraof these pulsars are found to steepen as Gamma = Gamma_max + alpha /sqrt(Edot), with Gamma_max providing an observational limit on the spectralslopes of young rotation-powered pulsars. These results reveal basic propertiesof young pulsar systems, allow new observational constraints on models ofpulsar wind emission, and provide a means of predicting the energetics of suchsystems when lacking detected pulsations.Comment: 6 pages, 3 figures, 1 table, LaTex, emulateapj5.sty. To appear in the June 20, 2003 issue of the Astrophysical Journa