Full Polar Cap Cascade Scenario: Gamma‐Ray and X‐Ray Luminosities from Spin‐powered Pulsars

We modify polar cap cascade picture to include the ICS of the highergeneration pairs. In such a ``full-cascade'' scenario, not only theperpendicular portion of the energy of the pairs goes to high energy radiationvia SR, but the parallel portion of the energy of the pairs can also contributeto high energy emission via ICS with the soft thermal photons from either thefull neutron star surface or the hot polar cap. An important output of such ascenario is that the soft tail of the ICS spectrum can naturally result in anon-thermal X-ray component which can contribute to the luminosities observedby ROSAT and ASCA. Here we present an analytic description of such a full polarcap cascade scenario within the framework of Harding & Muslimov accelerationmodel. We present the theoretical predictions of the $\gamma$-ray luminosities,the thermal and non-thermal X-ray luminosities for the known spin-powered X-raypulsars. Our results show that the observed different dependences of the highenergy luminosities on the pulsar spin-down luminosities, i.e., $L_\gamma\propto (L_{\rm sd})^{1/2}$ and $L_x \sim 10^{-3} L_{\rm sd}$, are wellreproduced. Our model predicts that the {\em pulsed} soft X-rays in the ROSATband from most of the millisecond pulsars might be of thermal origin if thereis no strong multipole field components near the surfaces of these pulsars.Comment: 23 pages, emulateapj style, final version to appear in the Astrophysical Journa