Differences between radio-loud and radio-quiet gamma-ray pulsars as revealed by Fermi

By comparing the properties of non-recycled radio-loud $\gamma-$ray pulsars and radio-quiet $\gamma-$ray pulsars, we have searched for the differences between these two populations. We found that the $\gamma-$ray spectral curvature of radio-quiet pulsars can be larger than that of radio-loud pulsars. Based on the full sample of non-recycled $\gamma-$ray pulsars, their distributions of the magnetic field strength at the light cylinder are also found to be different. We notice that this might be resulted from the observational bias. In re-examining the previously reported difference of $\gamma-$ray-to-X-ray flux ratios, we found the significance can be hampered by their statistical uncertainties. In the context of outer gap model, we discuss the expected properties of these two populations and compare with the possible differences identified in our analysis.