A Multiwavelength Study on the High-energy Behavior of the Fermi/LAT Pulsars

Abstract

Using archival as well as freshly acquired data, we assess the X-ray behavior of the Fermi/Large Area Telescope γ-ray pulsars listed in the First Fermi source catalog. After revisiting the relationships between the pulsars' rotational energy losses and their X-ray and γ-ray luminosities, we focus on the distance-independent γ-to-X-ray flux ratios. When plotting our F _γ/F _X values as a function of the pulsars' rotational energy losses, one immediately sees that pulsars with similar energetics have F _γ/F _X spanning three decades. Such spread, most probably stemming from vastly different geometrical configurations of the X-ray and γ-ray emitting regions, defies any straightforward interpretation of the plot. Indeed, while energetic pulsars do have low F _γ/F _X values, little can be said for the bulk of the Fermi neutron stars. Dividing our pulsar sample into radio-loud and radio-quiet subsamples, we find that, on average, radio-quiet pulsars do have higher values of F _γ/F _X , implying an intrinsic faintness of their X-ray emission and/or a different geometrical configuration. Moreover, despite the large spread mentioned above, statistical tests show a lower scatter in the radio-quiet data set with respect to the radio-loud one, pointing to a somewhat more constrained geometry for the radio-quiet objects with respect to the radio-loud ones.