The curved X-ray spectrum of PSR B1509-58 observed with BeppoSAX

We report timing and spectral results for PSR B1509-58 observed by BeppoSAX in February 1998. We obtained pulse profiles with high statistical signifi cance from 0.1 to 300 keV that exhibit the well-known broad asymmetric sing le pulse. The shape of this pulse does not change across this energy window and can be described as the sum of a narrow and a broader Gaussian compone nt separated similar to 0.13 in phase. The spectral distribution can be acc urately represented, over the entire BeppoSAX energy range, by a curved fun ction rather than a simple power-law shape. The extrapolation of this model to higher energies is also consistent with the COMPTEL fluxes in the 0.75- 30 MeV range, with the maximum luminosity for the broad pulse of PSR B1509- 58 reached at similar to 5.4 MeV. The comparison with the Crab pulsar spect rum suggests a possible origin of the X-ray emission in terms of synchrotro n radiation from secondary pair particles near the neutron star.