Cosmic Gamma Radiation

Many review articles and topics related to gamma-ray astronomy start with a statement that the 7-ray domain of cosmic radiation is the last of the electromagnetic windows to be opened. This concerns not only the first papers written several decades ago by the pioneers of gamma-ray astronomy, but also the recent assessments of the status […]

Energy Domains of Gamma Ray Astronomy (Cosmic Gamma Radiation)

Returning back to the question of the "last window", we notice that it covers at least 14 decades in frequency ! The energy domain of gamma-ray astronomy spans from approximately The lower bound characterises the region of nuclear Y-ray lines, as well as the electron-positron annihilation line. The second bound characterises the energy of highest […]

Low Energy Gamma Ray Sources (Cosmic Gamma Radiation)

This topic presents a brief overview of the achievements of observational gamma-ray astronomy in different energy bands. The status of space-based gamma-ray astronomy in the low energy (LE) and high energy (HE) regimes are discussed in Sections 2.1 and 2.2. Comprehensive description of the results at MeV and GeV energies obtained basically with BATSE, OSSE, […]

Gamma Ray Astronomy: A Discipline in Its Own Right (Cosmic Gamma Radiation)

High energy 7-rays combine three characteristics that make these energetic photons ideal carriers of information about nonthermal relativistic processes in astrophysical settings: (i) copious production in many galactic and extragalactic objects due to effective acceleration of charged particles and their subsequent interactions with the ambient gas, low frequency radiation, and magnetic fields; (ii) free propagation […]

High Energy Gamma Ray Sources (Cosmic Gamma Radiation)

At energies above 30 MeV, detection of cosmic Y-rays becomes significantly easier. The detection principle is based on conversion of the primary photon to an electron-positron pair, and on subsequent measurements of the tracks of secondary electrons with tracking detectors and their energy with a total-absorption calorimeter. This technique, originally developed for particle accelerator experiments, […]

The Status of Ground-Based Gamma Ray Astronomy (Cosmic Gamma Radiation) Part 1

Brief historical review Gamma-rays interacting with the Earth’s atmosphere initiate electromagnetic cascades. At sufficiently high energies the number of cascade particles is sufficient to obtain adequate information about the energy, direction and type of primary particles based on the study of spatial and temporal properties of secondary cascade products. Therefore the arrays of particle (electron, […]

The Status of Ground-Based Gamma Ray Astronomy (Cosmic Gamma Radiation) Part 2

Gamma rays from supernova remnants It is believed that cosmic rays below the so-called "knee" around 1 PeV have galactic origin and are produced in shell-type SNRs. The arguments leading to this important statement are, however, indirect and rather circumstantial. If SNRs are the principal sources of galactic cosmic rays providing the bulk of the […]

The Status of Ground-Based Gamma Ray Astronomy (Cosmic Gamma Radiation) Part 3

Other extragalactic objects Although the TeV blazars were not initially predicted as TeV emitters, now it is clear that the discovery of large TeV fluxes from these distant objects was possible because of the relativistic bulk motion of Y-ray production regions towards the observer, leading to the Doppler boosting of fluxes by several orders of […]

Interactions with Matter (Cosmic Gamma Radiation)

Any interpretation of an astronomical observation requires, by definition, unambiguous identification of the relevant radiation mechanism(s). The adequate knowledge of the features of the principal radiation processes is another key issue. Therefore the physics of radiation and absorption mechanisms is one of the central subjects of astronomy. With some exceptions, all basic radiation processes relevant […]

Interactions with Photon Fields (Cosmic Gamma Radiation) Part 1

The interaction of relativistic electrons with radiation fields through inverse Compton scattering provides one of the principal Y-ray production processes in astrophysics. It works effectively almost everywhere, from compact objects like pulsars and AGN to extended sources like supernova remnants and clusters of galaxies. Because of the universal presence of the 2.7 K CMBR, as […]