Diffuse 0.5-1 keV X-Rays and Nuclear Gamma Rays from Fast Particles in the Local Hot Bubble

We show that interactions of fast particles with the boundary shell of the local hot bubble could make an important contribution to the 0.5-1 keV diffuse X-ray background observed with ROSAT. The bulk of these nonthermal X-rays are due to line emission from fast O ions of energies around 1 MeV nucleon-1. The unequivocal signature of lines from de-excitations in fast ions is their large width (δE/E≃0.1 for O lines), which distinguishes them from X-ray lines produced in a hot plasma. If the 0.5-1 keV nonthermal X-rays are produced by accelerated particles with a sufficiently hard energy spectrum, the gamma-ray line emission produced in the boundary shell of the local hot bubble could account for the recently reported COMPTEL observations of nuclear gamma-ray lines from a broad region toward the Galactic center.