Gamma ray line emission from nuclear deexcitation following ener getic particle reactions is evaluated. The compiled nuclear data and the calculated gamma ray spectra and intensities can be used for the study of astrophysical sites which contain large fluxes of energetic protons and nuclei. A detailed evaluation of gamma ray line production in the interstellar medium is made in the present paper.

No abstract

Observations of Be and B in low-metallicity halo stars formed during the Ðrst 109 yr of Galactic evolution show that cosmic-ray acceleration must have taken place in the early Galaxy. The observed abundances of these elements relative to Fe, which, in the early Galaxy, is almost exclusively produced in Type II supernovae, strongly suggest that the cosmic-ray acceleration is also related to such supernovae with the particles being accelerated out of freshly nucleosynthesized matter before it mixes into the ambient, essentially nonmetallic interstellar medium. The observed abundances require that about 3 ] 1049 to 2 ] 1050 ergs per Type II supernova be imparted to these metallic cosmic rays, depending on whether or not H and He are accelerated along with the metals. The current data, however, are not sufficient to decide whether these cosmic rays are predominantly low energy or high energy. But, in any case, arguments of energetics imply a hard-energy spectrum extending up in energy to at least 50 MeV nucleon~1. This rules out Be and B production by supernova ejecta without further acceleration. In addition to production by cosmic rays, there must also be signiÐcant 11B production by neutrinos. This argument is driven by the observed 11B/10B ratio in meteorites that is very difficult to reproduce by cosmic-ray interactions. Observations of 6Li and Li in the early Galaxy provide information on the acceleration of nonmetallic cosmic rays out of the interstellar medium.

We present the 2-60 keV spectrum of the supernova remnant Cassiopeia A measured using the Proportional Counter Array and the High Energy X-ray Timing Experiment on the Rossi X-ray Timing Explorer satellite. In addition to the previously reported strong emission-line features produced by thermal plasmas, the broad-band spectrum has a high-energy "tail" that extends to energies at least as high as 120 keV. This tail may be described by a broken power law that has photon indices of Γ 1 = 1.8 +0.5 −0.6 and Γ 2 = 3.04 +0.15 −0.13 and a break energy of E b = 15.9 +0.3 −0.4 keV. We argue that the high-energy component, which dominates the spectrum above about 10 keV, is produced by synchrotron radiation from electrons that have energies up to at least 40 TeV. This conclusion supports the hypothesis that Galactic cosmic rays are accelerated predominantly in supernova remnants.

We suggest that the cosmic rays are accelerated primarily out of the supernova ejecta-enriched matter in the interiors of superbubbles. These hot, low-density superbubbles, which reach dimensions of several hundred parsecs, are generated by the winds and ejecta of supernova explosions of massive stars formed in giant molecular cloud OB associations that last for tens of megayears. Since these bubbles expand with shell velocities that are much faster than the dispersion velocities of the O and B star progenitors of the supernovae that power the bubbles, the bulk of the supernovae occur in their cores. The expanding remnants of each of these supernovae fill only less than 1% of this core before they have slowed to sonic velocities. Thus, the bulk of these supernovae remnants, together with their metal-rich grain and gas ejecta and their cosmic-ray-accelerating shocks, are well confined within the cores of superbubbles. These cores can thus provide a source of cosmic-ray matter of essentially constant metallicity throughout the age of the Galaxy, which is required to account for the constancy of cosmicray-produced Be relative to supernova-produced Fe observed in halo stars formed in the early Galaxy. The interactions of the grains and gas in metal-rich superbubbles, with recurrent supernova shocks every ∼ 5 3 # 10 yr, also reconcile the requirement of a supernova ejecta source of cosmic rays with the recent observations that require a greater than 10 5 yr delay between nucleosynthesis and acceleration for the cosmic-ray metals. Supernovaenriched bubble metallicity may also explain the X-ray emission from the interiors of superbubbles in the Large Magellanic Cloud.