High-Altitude Emission from Pulsar Slot Gaps: The Crab Pulsar

We present results of a 3D model of optical to γ-ray emission from the slot gap accelerator of a rotation-powered pulsar. Primary electrons accelerating to high-altitudes in the unscreened electric field of the slot gap reach radiationreaction limited Lorentz factors of ∼ 2× 10, while electron-positron pairs from lower-altitude cascades flow along field lines interior to the slot gap. The curvature, synchrotron and inverse Compton radiation of both primary electrons and pairs produce a broad spectrum of emission from infra-red to GeV energies. Both primaries and pairs undergo cyclotron resonant absorption of radio photons, allowing them to maintain significant pitch angles. Synchrotron radiation from pairs with a power-law energy spectrum from γ = 10 − 10, dominate the spectrum up to ∼ 10 MeV. Synchrotron and curvature radiation of primaries dominates from 10 MeV up to a few GeV. We examine the energy-dependent pulse profiles and phase-resolved spectra for parameters of the Crab pulsar as a function of magnetic inclination α and viewing angle ζ , comparing to broad-band data. In most cases, the pulse profiles are dominated by caustics on trailing field lines. We also explore the relation of the high-energy and the radio profiles, as well as the possibility of caustic formation in the radio cone emission. We find that the Crab pulsar profiles and spectrum can be reasonably well reproduced by a model with α = 45 and ζ ∼ 100 or 80. This model predicts that the slot gap emission below 200 MeV will exhibit correlations in time and phase with the radio emission. Subject headings: pulsars: general — radiation mechanisms: nonthermal — acceleration of particles — stars: neutron — X-rays: stars — gamma rays: theory Astrophysics Science Division, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 Stony Brook University, Stony Brook, NY Nicolaus Copernicus Astronomical Center, Torun, Poland Current address: [email protected]