DIFFERENCES BETWEEN RADIO-LOUD AND RADIO-QUIET γ-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 radioquiet 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 note that this might result from an observational bias. By reexamining the previously reported difference of gamma-ray-to-X-ray flux ratios, we found that the significance can be hampered by their statistical uncertainties. In the context of the outer gap model, we discuss the expected properties of these two populations and compare with the possible differences that are identified in our analysis.