The X-ray spectrum of the plerionic system PSR B1509-58/MSH 15-52

We present the results of observations of the PSR B1509-58/MSH 15-52 system in X-rays (2-250 keV) by the Rossi X-Ray Timing Explorer. The spectra of the peak of the pulsed component (radio phase 0.17-0.53) is fitted by a power law of photon index 1.36 ± 0.01, with no evidence of a high-energy spectral break seen up to ∼200 keV. For the off-pulse spectral component, the spectrum from 2-250 keV is fitted by a power law of photon index 2.215 ± 0.005. An iron emission line at 6.7 keV with an equivalent width of 129 eV improves the fit, but only at a marginal significance. Thermal bremsstrahlung and Raymond-Smith models produce much worse fits to the unpulsed data. The lack of a high-energy spectral break in the pulsed emission implies an efficiency of ≥3% in the conversion of pulsar spin-down energy to pulsed X-rays in the system.