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 thelocal hot bubble could make an important contribution to the 0.5-1 keV diffuseX-ray background observed with ROSAT. The bulk of these nonthermal X-rays aredue to line emission from fast O ions of energies around 1 MeV/nucleon. This isthe typical energy per particle in the ejecta of the supernova which is thoughtto have energized the bubble. We find that there is sufficient total energy inthe ejecta to produce X-rays of the required intensity, subject to the detailsof the evolution of the fast particle population since the supernova explosion(about 3 10$^5$ years ago based on the age of the Geminga pulsar). Theunequivocal signature of lines from deexcitations in fast ions is their largewidth ($\delta E/E$~0.1 for O lines), which will clearly distinguishes themfrom X-ray lines produced in a hot plasma. If a small fraction of the totalejecta energy is converted into accelerated particle kinetic energy (>~30MeV/nucleon), the gamma-ray line emission produced in the boundary shell of thelocal hot bubble could account for the recently reported COMPTEL observationsof nuclear gamma-ray lines from a broad region towards the Galactic center.Comment: 13 pages, 4 figures, submitted to Ap