Pulsars And Nebula High-energy Physics Process Research

Pulsars are rapidly spinning and highly magnetised neutron stars, which play important roles in the high-energy astrophysics. In this paper, I first give a brief review about the observations and theoretical models of the pulsars and pulsar wind nebulae. And then I introduced our studies of the high-energy processes of pulsars and pulsar wind nebulae (PNWe), including (Ⅰ) the one-dimentional electric field structure of an non-vacuum outer gap accelerator;(Ⅱ)the diffuse neutrino emission from the Galactic young pulsars;(Ⅲ) the nonthermal high-energy radiation from millisecond pulsars based on a revised outer gap model; and (Ⅳ) the nonthermal emission from pulsar wind nebulae. The main results of these works are as follows:1. We re-study one-dimensional electric field structure of an outer gap accel-erator by considering physical limit of trans-field height. Inside the outer gap, the charge depletion creates a large electric field along the magnetic field lines. Electrons and/or positrons are accelerated to ultra-relativistic en-ergies by this longitudinal electric field, and then radiate γ-ray photons by curvature radiation. The collision of these γ-rays and ambient X-ray photons further produce radiating particles, resulting in a stationary gap. We solve the structure of this longitudinal electric field together with the distribution of electrons and positrons and γ-ray photons for an aligned rotator. Our results indicate that the outer gap can extend to the light cylinder using reasonable parameters.2. Young pulsars with ages less than106yr can accelerate protons to relativistic energies above the polar cap region if the magnetic moment anti-parallel to the spin axis. The interaction of those protons with the soft X-ray photons coming from the neutron star surface can produce high energy muon neutri-nos through photomeson production. Therefore, those pulsars are promising candidates as high energy neutrino sources. We produce a sample of young pulsars in our Galaxy using a Monte Carlo method, determine whether they are potential neutrino pulsars and calculate the total neutrino fluxes from those young pulsars using the Link&Burgio (LB) model. We obtain the upper limit of the diffuse neutrino flux from the young pulsars in the Galaxy, and compare it with predicted results from active galactic nuclei (AGNs) and gamma-ray bursts (GRBs).3. We study the high-energy radiation from millisecond pulsars (MSPs) based on the revied outer gap model, which have taken the effects of the magnetic inclination angles and magnetic geometry into account. In the revised version of our outer gap model, a strong multipole magnetic field exists near the stellar surface, the X-rays are produced by the backflow current of the outer gap, and consist of one power-law and two thermal components. These X-rays collide with high-energy photons inside the outer gap to sustain the outer gap, and then high-energy γ-rays are produced in the outer gap. The fractional size of the outer gap is the function of the radial distance to the neutron star and the magnetic inclination angle for a given millisecond pulsar. We have applied this model to account for the pulsed X-ray emission from the MSPs outside of and in the globular cluster47Tuc, the modeled X-ray luminosity are consistent with the observed. These two types of MSPs have different relation between the X-ray luminosity with the spin-down power.We also applied our model to predict the averaged high-energy γ-ray fluxes and compare them with the sensitivity of the AGILE and the GLAST (now Fermi Gamma-ray Space Telescope). Fermi LAT has detected more than40gamma-ray MSPs, we study the gamma-ray properties of these MSPs based on the revised outer gap model. Assuming that high-energy emission at an averaged radius of the field line in the center of the outer gap with a Gaussian distribution of the parallel electric field along the gap height represents typical emission, the phase-averaged gamma-ray spectrum for a given pulsar can be estimated. We apply the model to explain the phase-averaged spectra of20MSPs with known periods and period derivatives.4. We study the non-thermal emission of pulsar wind nebulae (PWNe) from radio to TeV γ-ray bands on a simplified time-dependent injection model. In this model, a relativistic wind of particles driven by a central pulsar with a spin-down power L(t) goes into the ambient medium and a shock wave is formed to accelerate the particles to very high energies through the Fermi acceleration mechanism in the PWN. Therefore, the relativistic particles in the PWN consist of two components, one come directly from pulsar magneto-sphere, another from the shock acceleration in the PWN. A time-dependent injected spectrum in the PWN has a broken power law with different indices and a break energy Eb. The accelerated particles emit nonthermal photons through synchrotron and inverse Compton scattering off soft photon fields. We applied this model to Crab nebula, PWN in MSH15-52and HESS J1825-137which have been detected to emit very high energy photons. Our results indicate that (i) the observed data ranging from radio to VHE γ-rays for the Crab nebula can be reproduced in this model, where the emission from radio to medium γ-rays is from the synchrotron emission from the injected electrons, whereas the high-energy photons primarily come from the inverse Compton scattering of the high-energy electrons on synchrotron photons; and (ii) TeV emission for the PWN in MSH15-52and HESS J1825-137mainly come from the inverse Compton scattering of the high-energy electrons on infrared photons.