THEORETICAL STUDY OF COSMIC RAY ASTROPHYSICS

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1. The site and mechanism of cosmic ray acceleration are studied. The attainable maximum energy for oblique shocks, where the magnetic field direction and the shock normal is not parallel, is estimated analytically. It turns out to be 10^<16> and 10^<20>eV for supernova remnants and radio galaxies, respectively, which possibly resoved the long standing problem. Further, I have made Monte Carlo simulations, which confirmed the analytic estimates. Geometrical effects on the acceleration process is under investigation.2. I studied a possibility to observationally confirm the acceleration theory. Since the cosmic ray spectrum at the acceleration site is expected to be much flatter than that observed on the earth, the gamma-ray spectrum emitted at the acceleration site should also be flat. I calculated expected gamma-ray flux from supernova remnants, and found that the flux is just below the detection limit of existing instruments and can be observable by Cerenkov telescopes and EAS arrays under construction.3. I also studied GeV gamma-ray emission from blazars which have recently been discovered by EGRET on board CGRO satellite. I argued that gamma-rays are produced by the inverse Compton scattering off soft photons by relativistic electrons in a beamed jet. I applied shock acceleration theory to this problem ; I found that a break in the electron spectrum should appear due to radiative cooling and that this break corresponds to the photon energy of around 10MeV for 3C279.