There is a growing new class of young spin-down powered pulsars called GeV-quiet soft gamma-ray pulsar ; ( 1 ) spectral turnover appears around 10MeV , ( 2 ) the X-ray spectra of below 20 keV can be described by power law with photon index around 1.2 and ( 3 ) the light curve in X-ray/soft gamma-ray bands shows single broad pulse .
Their emission properties are distinct from the normal gamma-ray pulsars , for which the spectral peak in \nu F _ { \nu } appears in GeV energy bands and the X-ray/gamma-ray light curves show sharp and double ( or more ) peaks .
In this paper , we discuss that X-ray/soft gamma-ray emissions of the GeV-quiet soft gamma-ray pulsars are caused by the synchrotron radiation of the electron/positron pairs , which are created by the magnetic pair-creation process near the stellar surface .
In our model , the viewing geometry is crucial factor to discriminate between the normal gamma-ray pulsars and soft gamma-ray pulsars .
Our model suggests that the difference between the magnetic inclination angle ( \alpha ) and the Earth viewing angle ( \beta ) of the soft gamma-ray pulsars is small , so that the synchrotron emissions from the high magnetic field region around the polar cap region dominates in the observed emissions .
Furthermore , the inclination angle of the soft gamma-ray pulsar is relatively small , \alpha \leq 30 degree , and our line of sight is out of the gamma-ray beam emitted via the curvature radiation process in the outer gap .
We also analysis the six year Fermi data for four soft gamma-ray pulsars to determine the upper limit of the GeV flux .