We observed PSR B1259 - 63 , a young non-accreting pulsar orbiting around a Be star SS 2883 , eight times with the Suzaku satellite from July to September 2007 , to characterize the X-ray emission arising from the interaction between a pulsar relativistic wind and Be star outflows .
The X-ray spectra showed a featureless continuum in 0.6–10 keV , modeled by a power law with a wide range of photon index 1.3–1.8 .
When combined with the Suzaku PIN detector which allowed spectral analysis in the hard 15–50 keV band , X-ray spectra do show a break at \sim 5 keV in a certain epoch .
Regarding the PSR B1259 - 63 system as a compactified pulsar wind nebula , in which e ^ { \pm } pairs are assumed to be accelerated at the inner shock front of the pulsar wind , we attribute the X-ray spectral break to the low-energy cutoff of the synchrotron radiation associated with the Lorentz factor of the relativistic pulsar wind \gamma _ { 1 } \sim 4 \times 10 ^ { 5 } .
Our result indicates that Comptonization of stellar photons by the unshocked pulsar wind will be accessible ( or tightly constrained ) by observations with the Fermi Gamma-ray Space Telescope during the next periastron passage .
The PSR B1259 - 63 system allows us to probe the fundamental properties of the pulsar wind by a direct means , being complementary to the study of large-scale pulsar wind nebulae .