Institute for the Application of Geospatial Technology

Excitation of a Global Alfven wave (GAW) is proposed as a viable mechanism to explain plasma heating in the magnetosphere of young stars. The wave and basic plasma parameters are compatible with the requirement that the dissipation length of GAWs be comparable to the distance between the shocked region at the star's surface and the truncation region in the accretion disk. A two-fluid magnetohydrodynamic plasma model is used in the analysis. A current carrying filament along magnetic field lines acts as a waveguide for the GAW. The current in the filament is driven by plasma waves along the magnetic field lines and/or by plasma crossing magnetic field lines in the truncated region of the disk of the accreting plasma. The conversion of a small fraction of the kinetic energy into GAW energy is sufficient to heat the plasma filament to observed temperatures.

A grid of composite models for the narrow line region of active galaxies, which consistently account for both the effect of a photoionizing radiation from the active center and of a shock front, is presented. Theoretical results, calculated with the SUMA code, are given for different values of shock velocities, preshock densities, geometrical thickness of the clouds, and, particularly, for the ionizing radiation intensity in a large range. The input parameters are chosen within the ranges indicated by previous fits of several observed emission-line and continuum spectra from active galaxies. Shock velocities from 100 \kms ~to 1500 \kms ~and preshock densities from 100 \cm3 to 1000 \cm3 are considered. The line intensities of the most important ultraviolet, optical and infrared transitions are obtained and are listed in several tables.

Using the cosmic ray (CR) data available in the energy interval $(10 - 2 \times 10^{7})$ GeV/particle, we have calculated the profile of the primary $\gamma$-ray spectrum produced by the interaction of these CR with thermal nuclei of the ISM. Normalized to the EGRET measurements, this allows an estimate of the galactic diffuse $\gamma$-ray background due to intermediate and high energy CR at TeV energies. On the other hand, over the last few years, several particles with energies above $10^{20}$ eV (beyond the Greisen-Zatsepin-Kuzmin cut-off) have been detected. These particles are very likely extragalactic protons originated at distances not greater than $30 - 50$ Mpc [e.g., 1]. The propagation of these ultra-high energy protons (UHEP) through the intergalactic medium leads to the development of $\gamma$-ray cascades and an ultimate signature at TeV energies. To assess the statistical significance of this $\gamma$-ray signature by the UHEP, we have also simulated the development of electromagnetic cascades triggered by the decay of a $10^{19}$ eV $\pi^{o}$ in the intergalactic medium after an UHEP collision with a cosmic microwave background photon.