Cosmic Gamma Radiation

Interactions with Photon Fields (Cosmic Gamma Radiation) Part 2

Interactions of hadrons with radiation fields In astrophysical environments the radiation density often exceeds the density of gas component. In these conditions the interactions of high energy hadrons with radiation can dominate over interactions with matter, albeit the relevant cross-sections are relatively small. The main processes of hadron-photon interactions include (i) inverse Compton scattering:(ii) electron-positron […]

Interactions with Magnetic Fields (Cosmic Gamma Radiation)

Synchrotron radiation and pair-production Many important results of the theory of synchrotron radiation are obtained within the framework of classical electrodynamics (see e.g. Jackson, 1975). The classical treatment of the synchrotron radiation is limited by the condition whereis the so-called critical value of the magnetic field relevant to quantum effects. Generally, the energy of synchrotron […]

Relativistic Electron-Photon Cascades (Cosmic Gamma Radiation)

Relativistic electrons – directly accelerated, or secondary products of various hadronic processes – may result in copious Y-ray production caused by interactions with ambient targets in forms of gas (plasma), radiation and magnetic fields. In different astrophysical environments Y-ray production may proceed with high efficiency through bremsstrahlung, inverse Compton scattering and synchrotron (and/or curvature) radiation, […]

Origin of Galactic Cosmic Rays: General Remarks (Cosmic Gamma Radiation)

Since the discovery of Cosmic Rays (CRs) by Victor Hess in 1912, the origin of this radiation has remained a mystery. Despite extensive efforts we still do not have a coherent theory which can explain a great variety of the features of CRs. What do we know about Cosmic Rays? Actually, we know a lot. […]

Giant Molecular Clouds as Tracers of Cosmic Ray (Cosmic Gamma Radiation) Part 1

The first studies of the diffuse galactic Y-radiation by the SAS-2 and COS B satellite missions revealed a relatively small, by a factor of < 2, spatial gradient of CRs in the Galactic Disk (see e.g. Bloemen, 1989). EGRET measurements generally confirm this conclusion (Hunter et al., 1997a). A small variation of the CR density […]

Giant Molecular Clouds as Tracers of Cosmic Ray (Cosmic Gamma Radiation) Part 2

Gamma rays from a cloud near the accelerator One of the principal parameters determining the Y-ray visibility of GMCs is is the diffuse mass of a GMC in units of 105 solar masses, andAssuming that Y-rays are produced by interactions of CRs with the ambient gas, whereis the Y-ray emissivity. In a "passive" GMC, i.e. […]

Probing the Sources of VHE CR Electrons (Cosmic Gamma Radiation)

The standard interpretation of the energy spectrum of CRs usually assumes a uniform and continuous distribution of sources in the Galaxy both in space and time. Whereas for the nucleonic component of CRs this approximation can be considered as a reasonable (although not undisputable) working hypothesis, the validity of this assumption for the electrons is […]

Diffuse Radiation from the Galactic Disk (Cosmic Gamma Radiation) Part 1

The study of diffuse galactic Y-ray emission, i.e. the radiation components produced in interactions of electronic and nucleonic components of CRs with the interstellar gas and photon fields, provides information about the density and energy spectra of CRs in different parts of the Galactic Disk, and thus provides a key insight into the character of […]

Diffuse Radiation from the Galactic Disk (Cosmic Gamma Radiation) Part 2

Electron bremsstrahlung Below 1 GeV, bremsstrahlung Y-rays are produced by the same electrons responsible for the galactic synchrotron radio emission. Therefore the differential flux J(E) of this radiation in the region from 30 MeV to ~ 1 GeV should have a characteristic power-law slope with an index coinciding with the spectral index of the radio […]

Gamma Rays as a Diagnostic Tool (Cosmic Gamma Radiation)

For more than 40 years, the galactic SNRs have been believed to be the sites of production of the bulk of the observed CR flux. The strong shocks in SNRs may provide – through the diffusive shock acceleration mechanism – very effective, up to 10 to 30 per cent, conversion of the total SN explosion […]