Gamma-ray astronomy and cosmic ray origin problem

The purpose of this talk is to review some recent work on the model for the origin of the bulk of Galactic cosmic rays (CRs), namely that they are produced by diffusive shock acceleration in shock waves associated with supernova remnants (SNRs). This is currently the modern theory for the origin of Galactic CRs. Selfconsistent nonlinear theory of CR acceleration in SNRs developed during the last decade explains the main characteristics of the observed CR spectrum at least up to the knee energy. Direct information about CR population in young Galactic SNRs obtained from the properties of the nonthermal radiation is analysed. Electron CR component is visible ia a wide range of radiation, which they produce in SNRs, from radio to gamma-ray emission, whereas in the case of nuclear CR component gamma-rays detection is the only possibility to see it. If this nuclear component is strongly enhanced inside SNRs then through inelastic nuclear collisions, leading to pion production and subsequent decay, gamma-rays will be produced at the detectable level. It is argued that the existing data confirm very efficient acceleration of nuclear CRs in SNRs with the efficiency consistent with the requirements for the Galactic CR energy budget and that the theory is not only able to describe the CR dynamics and acceleration in SNRs, but that it constitutes in addition a reliable method to quantitatively determine the effective (strongly amplified) SNR magnetic field strength which is produced in the acceleration process.