The GALPROP model for cosmic-ray propagation is able to make explicit predictions for the distribution of galactic diffuse gamma-rays. We compare different propagation models with gamma-ray spectra measured by EGRET for various regions of the sky. This allows sensitive tests of alternative explanations for the apparent excess emission observed at GeV gamma-rays. We find that a population of har...

The origin of the particles in the highest energy end of the cosmic ray spectrum is discussed in the context of the wider problem of the origin of the whole cosmic radiation as observed at the Earth. In particular we focus our attention on the acceleration problem and on the transition from galactic to extragalactic cosmic rays.

High energy protons produced by various sources of cosmic rays, e.g., supernova remnants, pulsar wind nebulae, active galactic nuclei and gamma-ray bursts, participate in pγ and pp interactions. Although pp interactions may be the dominant mechanism in our Galaxy, it is unclear how important pγ process is. We show that the upper bound on the fraction of total number of protons participating in ...

We address some current theoretical issues around ultra-high energy cosmic rays. We recall that scenarios producing more γ−rays than cosmic rays up to high redshift can in general only provide a sub-dominant contribution to the ultra-high energy cosmic ray flux. This includes extra-galactic top-down and the Z-burst scenarios. Finally we discuss the influence of large scale cosmic magnetic field...

We present 74 MHz radio continuum observations of the Galactic center region. These measurements show nonthermal radio emission arising from molecular clouds that is unaffected by free–free absorption along the line of sight. We focus on one cloud, G0.13-0.13, representative of the population of molecular clouds that are spatially correlated with steep spectrum (α(327MHz)(74MHz) = 1.3 ± 0.3) no...

The rare isotope Li is made only by cosmic rays, dominantly in αα → Li fusion reactions with ISM helium. Consequently, this nuclide provides a unique diagnostic of the history of cosmic rays in our Galaxy. The same hadronic cosmic-ray interactions also produce high-energy γ rays (mostly via pp → π → γγ). Thus, hadronic γ-rays and Li are intimately linked. Specifically, Li directly encodes the l...

Gamma ray emission lines resulting from accelerated particle bombardment of ambient gas can serve as an important spectroscopic tool for abundance determinations. The method is illustrated by considering the gamma ray line emission observed from solar flares. The observation of similar gamma ray lines from Orion suggests the existence of large fluxes of low energy Galactic cosmic rays. The role...