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There is a growing new class of young spin-down powered pulsars calledGeV-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 photonindex around 1.2 and (3) the light curve in X-ray/soft gamma-ray bands showssingle broad pulse. Their emission properties are distinct from the normalgamma-ray pulsars, for which the spectral peak in $\nu F_{\nu}$ appears in GeVenergy bands and the X-ray/gamma-ray light curves show sharp and double (ormore) peaks. In this paper, we discuss that X-ray/soft gamma-ray emissions ofthe GeV-quiet soft gamma-ray pulsars are caused bythe synchrotron radiation ofthe electron/positron pairs, which are created by the magnetic pair-creationprocess near the stellar surface. In our model, the viewing geometry is crucialfactor to discriminate between the normal gamma-ray pulsars and soft gamma-raypulsars. Our model suggests that the difference between the magneticinclination angle ($\alpha$) and the Earth viewing angle ($\beta$) of the softgamma-ray pulsars is small, so that the synchrotron emissions from the highmagnetic field region around the polar cap region dominates in the observedemissions. Furthermore, the inclination angle of the soft gamma-ray pulsar isrelatively small, $\alpha\leq 30$~degree, and our line of sight is out of thegamma-ray beam emitted via the curvature radiation process in the outer gap. Wealso analysis the six year $Fermi$ data for four soft gamma-ray pulsars todetermine the upper limit of the GeV flux.

Emission mechanism of GeV-quiet soft gamma-ray pulsars; A case for peculiar geometry?