High-energy Universe Research Articles

High energy gamma rays

This article reviews the present status of high energy γ-ray astronomy at energies above 30 MeV. Observations in the past decade using both space- and ground-based experiments have been primarily responsible for giving a tremendous boost to our knowledge of the high energy Universe. High energy γ-rays have been detected from a wide range of Galactic and extragalactic astrophysical sources, such as γ-ray bursters, pulsars, and active galaxies. These observations have established high energy γ-ray astronomy as a vital and exciting field, that has a bright future. This review summarizes the experimental techniques, observations and results obtained with recent experiments, and concludes with a short description of future prospects.

High energy universe — Satellite missions

A variety of satellite missions to observe the high energy universe are currently operating and some more with more versatility and capability are on the anvil. In this paper, after giving a brief introduction to the constituents of the high energy universe and the related plasma physical problems, general as well as specific features of the current and future x-ray and gamma-ray satellite missions are described.

Very-high-energy Gamma-ray Sources

Gamma-ray photons at TeV energies have been observed in recent years from a special class of active galactic nuclei, the so-called BLAZARS. The maximum photon energy observed is now approaching energies beyond 10 TeV, opening up new windows into the high-energy universe.

An ancient revisits cosmology.

In this after-dinner speech, a somewhat light-hearted attempt is made to view the observational side of physical cosmology as a subdiscipline of astrophysics, still in an early stage of sophistication and in need of more theoretical understanding. The theoretical side of cosmology, in contrast, has its deep base in general relativity. A major result of observational cosmology is that an expansion of the Universe arose from a singularity some 15 billion years ago. This has had an enormous impact on the public's view of both astronomy and theology. It places on cosmologists an extra responsibility for clear thinking and interpretation. Recently, gravitational physics caused another crisis from an unexpected observational result that nonbaryonic matter appears to dominate. Will obtaining information about this massive nonbaryonic component require that astronomers cease to rely on measurement of photons? But 40 years ago after radio astronomical techniques uncovered the high-energy universe, we happily introduced new subfields, with techniques from physics and engineering still tied to photon detection. Another historical example shows how a subfield of cosmology, big bang nucleosynthesis, grew in complexity from its spectroscopic astrophysics beginning 40 years ago. Determination of primordial abundances of lighter nuclei does illuminate conditions in the Big Bang, but the observational results faced and overcame many hurdles on the way.

Charge Dependence of the Energy Spectra of Cosmic Rays

WHEN the abundance of elements in galactic cosmic rays is compared with the universal abundance1, galactic cosmic rays are found to be very highly enriched in heavier elements. A similar enrichment has been reported recently based on comparisons of solar energetic particles and solar photospheric and coronal abundances (ref. 2 and J. D. Sullivan, P. B. Price and H. J. Crawford at the Solar Physics Division meeting of AAS, Univ. Maryland, April 1972). The high energy universe composed of suprathermal particles is apparently richer in heavy nuclei than the thermal universe. The reason for this has been sought in the possible preferential acceleration of energetic particles of higher atomic number Z (refs 3 and 4). We report new experimental results in the energy range 3 to 50 GeV nucleon−1 which indicate that the well known enrichment of heavy nuclei in cosmic rays is increasing with increasing energy.