Composition and spectra of primary cosmic-ray electrons and nuclei above 10 10 eV

1975 ◽  
Vol 277 (1270) ◽  
pp. 349-363 ◽  
Keyword(s):  
Cosmic Ray ◽  
High Energy ◽  
Energy Spectra ◽  
Average Lifetime ◽  
Interstellar Space ◽  
Interstellar Matter ◽  
Electromagnetic Interactions ◽  
Nuclear Species ◽  
The Galaxy ◽  
High Energy Particles

Recent experiments have extended the knowledge of the flux and energy spectra of individual cosmic-ray components to much higher energies than had previously been accessible. Both electron and nuclear components show a behaviour at high energy which is unexpected, and which carries information regarding the sources and the propagation of particles between sources and observer. Electromagnetic interactions which are suffered by the electrons in interstellar space should steepen their spectrum, a steepening that would reveal the average lifetime a cosmic-ray particle spends in the galaxy. Measurements up to 1000 GeV show no such steepening. It was discovered that the composition of the nuclear species which is now measured up to 100 GeV/nucleon changes with energy. This change indicates traversal of less interstellar matter by the high energy particles than by those of lower energy. We discuss the experimental evidence and its implication.

scholarly journals Composition and Galactic Confinement of Cosmic Rays

1971 ◽  
Vol 2 ◽  
pp. 740-756
Author(s):  
Maurice M. Shapiro
Keyword(s):  
Cosmic Rays ◽  
Cosmic Ray ◽  
High Energy ◽  
Galactic Cosmic Rays ◽  
Interstellar Space ◽  
Heavy Nuclei ◽  
High Energy Astrophysics ◽  
Transit Times ◽  
The Galaxy ◽  
Path Lengths

The ‘Galactic’ cosmic rays impinging on the Earth come from afar over tortuous paths, traveling for millions of years. These particles are the only known samples of matter that reach us from regions of space beyond the solar system. Their chemical and isotopic composition and their energy spectra provide clues to the nature of cosmic-ray sources, the properties of interstellar space, and the dynamics of the Galaxy. Various processes in high-energy astrophysics could be illuminated by a more complete understanding of the arriving cosmic rays, including the electrons and gamma rays.En route, some of theprimordialcosmic-ray nuclei have been transformed by collision with interstellar matter, and the composition is substantially modified by these collisions. A dramatic consequence of the transformations is the presence in the arriving ‘beam’ of considerable fluxes of purely secondary elements (Li, Be, B), i.e., species that are, in all probability, essentially absent at the sources. We shall here discuss mainly the composition of the arriving ‘heavy’ nuclei -those heavier than helium - and what they teach us about thesourcecomposition, the galactic confinement of the particles, their path lengths, and their transit times.

scholarly journals Gamma-ray observations and massive stars

1999 ◽  
Vol 193 ◽  
pp. 205-217
Author(s):  
Roland Diehl
Keyword(s):  
Gamma Rays ◽  
Massive Star ◽  
Gamma Ray ◽  
Massive Stars ◽  
Cosmic Ray ◽  
Interstellar Space ◽  
Interstellar Matter ◽  
Spatial Profile ◽  
The Galaxy ◽  
Γ Ray

Gamma-rays from astrophysical sources testify energetic processes such as nucleosynthesis and cosmic ray collisions. Gamma-rays are observable from throughout the Galaxy, unattenuated by interstellar matter, provided their intensity exceeds the current instrumental sensitivity level (∼ 10−5ph cm−2s−1 at 1 MeV). Massive stars are at the origin of relevant sources: The all-sky image in the 1.809 MeV γ-ray line from radioactive 26Al traces nucleosynthesis throughout the Galaxy. The structure of this emission along the plane of the Galaxy suggests massive stars as dominating sources of this radioactivity. Discrimination of the contribution from core collapse supernova against that from WR-wind ejected hydrostatic nucleosynthesis products may be obtained from 60Fe γ-ray line observations, or from spatial-profile consequences of the metallicity dependence of 26Al production in theories for both source sites. As a single source, the nearest WR star in the γ2 Vel system is found to eject less 26Al into interstellar space than current theories predict. However, a more adequate comparison must be based on a time-dependent 26Al light-curve of the system. Furthermore, continuum γ-ray production in WR binaries through wind-wind interaction, and constraints on the low-energy cosmic ray origin in WR winds through characteristic nuclear deexcitation line studies are targets of research. Studies stimulated by COMPTEL'S 3–7 MeV excess report from the Orion region indicate that the γ-ray line measurements could separate the origins from supernova ejecta and wind material. The COMPTEL Orion result is now attributed chiefly to an instrumental artifact, and has been withdrawn. Nevertheless, the search for MeV emission from massive star clusters, as well as from interacting binaries such as WR 140, promises a unique test of particle acceleration scenarios related to the source mechanism for cosmic ray production.

scholarly journals The composition of galactic cosmic rays

1968 ◽  
Vol 46 (10) ◽  
pp. S544-S547 ◽  
Author(s):  
D. V. Reames ◽  
C. E. Fichtel
Keyword(s):  
Cosmic Rays ◽  
Cross Sections ◽  
Length Distribution ◽  
Cosmic Ray ◽  
High Energy ◽  
Galactic Cosmic Rays ◽  
Interstellar Space ◽  
Fermi Acceleration ◽  
Fixed Amount ◽  
The Galaxy

Recent measurements of low-energy galactic cosmic rays obtained on sounding rockets and satellites exhibit a composition different from that obtained for intermediate and high-energy radiation obtained at balloon altitudes. In particular the ratio of light to medium nuclei is observed to be 0.2–0.3 in the 50–100 MeV/nucleon interval as compared with values near 0.5 in the 200–500 MeV/nucleon region. Lower values of the ratios C/O, N/O, F/O, and odd-Z/even-Z are also found. In the light of these new measurements and of new measurements on the fragmentation cross sections for cosmic-ray nuclei in interstellar space, an attempt has been made to calculate the composition expected if similar source spectra are assumed. It is found that neither passage through a fixed amount of material nor an equilibrium condition (exponential path-length distribution) is adequate to explain the observed features. The effects of including other mechanisms such as rigidity-dependent escape from the galaxy and Fermi acceleration in interstellar space are evaluated.

Primary γ-rays

1975 ◽  
Vol 277 (1270) ◽  
pp. 365-379 ◽  
Keyword(s):  
Cosmic Rays ◽  
Cosmic Ray ◽  
High Energy ◽  
Structural Features ◽  
Galactic Cosmic Rays ◽  
Interstellar Space ◽  
Characteristic Energy ◽  
The Galaxy ◽  
Ray Density ◽  
Γ Rays

Within our Galaxy, cosmic rays can reveal their presence in interstellar space and probably in source regions by their interactions with interstellar matter which lead to γ-rays with a very characteristic energy spectrum. From the study of the intensity of the high energy γ radiation as a function of galactic longitude, it is already clear that cosmic rays are almost certainly not uniformly distributed in the Galaxy and are not concentrated in the centre of the Galaxy. The galactic cosmic rays appear to be tied to galactic structural features, presumably by the galactic magnetic fields which are in turn held by the matter in the arm segments and the clouds. On the extra-galactic scale, it is now possible to say that cosmic rays are probably not at the density seen near the Earth. The diffuse celestial γ-ray spectrum that is observed presents the interesting possibility of cosmological studies and possible evidence for a residual universal cosmic ray density, which is much lower than the present galactic cosmic-ray density.

Evidence for Large Scale Cosmic Ray Electron Gradients in the Galaxy

1976 ◽  
Vol 3 (1) ◽  
pp. 1-6 ◽  
Author(s):  
W. R. Webber
Keyword(s):  
Large Scale ◽  
Spiral Structure ◽  
Cosmic Ray ◽  
Point Sources ◽  
Interstellar Matter ◽  
Interstellar Gas ◽  
The Galaxy ◽  
Ray Density ◽  
Γ Rays ◽  
Γ Ray

In recent years observations of γ-ray emission from the disk of the galaxy have provided a new opportunity for research into the structure of the spiral arms of our own galaxy. In Figure 1 we show a map of the structure of the disk of the galaxy as observed for γ-rays of energy > 100 MeV by the SAS-2 satellite (Fichtel et al. 1975). The angular resolution of these measurements is ~ 3°, and besides two point sources at l = 190° and 265° several features related to the spiral structure of the galaxy are evident in the data. Most of these γ-rays are believed to arise from the decay of π° mesons produced by the nuclear interactions of cosmic rays (mostly protons) with the ambient interstellar gas. As a result, the γ-ray fluxes represent a measure of the line of sight integral of the product of the cosmic ray density NCR and the interstellar matter density N1

scholarly journals Cosmic ray e± at high energy

2019 ◽  
Vol 208 ◽  
pp. 04001 ◽  
Author(s):  
Kfir Blum ◽  
Annika Reinert
Keyword(s):  
Secondary Production ◽  
Primary Source ◽  
Cosmic Ray ◽  
High Energy ◽  
Radiative Energy ◽  
Energy Losses ◽  
Propagation Time ◽  
Interstellar Matter ◽  
Independent Evidence ◽  
Good Agreement

There is a commonly expressed opinion in the literature, that cosmic-ray (CR) e+ come from a primary source, which could be dark matter or pulsars. In these proceedings we review some evidence to the contrary: namely, that e+ come from secondary production due to CR nuclei scattering on interstellar matter. We show that recent measurements of the total e± flux at E ≲ 3 TeV are in good agreement with the predicted flux of secondary e±, that would be obtained if radiative energy losses during CR propagation do not play an important role. If the agreement between data and secondary prediction is not accidental, then the requirement of negligible radiative energy losses implies a very short propagation time for high energy CRs: tesc ≲. 105 yr at rigidities R ≳ 3 TV. Such short propagation history may imply that a recent, near-by source dominates the CRs at these energies. We review independent evidence for a transition in CR propagation, based on the spectral hardening of primary and secondary nuclei around R ~ 100 GV. The transition rigidity of the nuclei matches the rigidity at which the e+ flux saturates its secondary upper bound.

Electromagnetic Interactions of High-Energy Cosmic-Ray Muons

1971 ◽  
Vol 4 (3) ◽  
pp. 638-646 ◽  
Author(s):  
O. C. Allkofer ◽  
C. Grupen ◽  
W. Stamm
Keyword(s):  
Cosmic Ray ◽  
High Energy ◽  
Electromagnetic Interactions

The low-energy cosmic-ray nuclei and their propagation in interstellar space

1968 ◽  
Vol 46 (10) ◽  
pp. S553-S556 ◽  
Author(s):  
G. M. Comstock
Keyword(s):  
Additional Data ◽  
Cosmic Ray ◽  
Low Energy ◽  
Energy Spectra ◽  
Interstellar Space ◽  
Loss Measurement ◽  
Depletion Depth ◽  
Two Component ◽  
The University ◽  
Component Models

The differential energy spectra of the cosmic-ray nuclei helium, carbon, nitrogen, and oxygen above 30 MeV/nucleon, boron, neon, magnesium, and silicon above 50 MeV/nucleon, and the iron group above 100 MeV/nucleon, measured in October–December 1964 and May–June 1965 by the University of Chicago charged-particle telescope on board the OGO-I satellite (Comstock et al. 1966b), have been corrected to take account of the effective depletion depth of the gold–silicon solid-state detectors used for rate-of-energy-loss measurement. Additional data from October to December 1965 are included. The magnitudes and relative shapes of the spectra deduced by extrapolation to nearby interstellar space place important constraints on the allowed modes of interstellar propagation for these nuclei. Two-component models are shown to account for most of the observed properties of the interstellar cosmic-ray nuclei.

Cosmic Ray Positron Production by Gamma Ray Interactions on Starlight

1991 ◽  
Vol 9 (1) ◽  
pp. 115-117 ◽  
Author(s):  
A. Mastichiadis ◽  
R. J. Protheroe ◽  
S. A. Stephens
Keyword(s):  
Production Rate ◽  
Unit Volume ◽  
Gamma Ray ◽  
Cosmic Ray ◽  
High Energy ◽  
Local Region ◽  
Positron Energy ◽  
Average Production ◽  
The Galaxy ◽  
Positron Production

AbstractWe examine the production of cosmic ray positrons by photon-photon pair production of high-energy γ-rays on starlight photons. We start by calculating the production rate as a function of positron energy and distance from the Sun resulting from interactions with sunlight. The results are generalized to production on other types of star. We calculate the average production rate per unit volume averaged over the local region of the galaxy, and we estimate the contribution to the observed intensity from this process.

Cosmic-ray nuclei up to 10 10 eV/u in the galaxy

1975 ◽  
Vol 277 (1270) ◽  
pp. 319-348 ◽  
Keyword(s):  
Cosmic Rays ◽  
Solar System ◽  
Cross Sections ◽  
Cosmic Ray ◽  
Interstellar Space ◽  
Heavy Nuclei ◽  
Hydrogen Atoms ◽  
Interstellar Gas ◽  
The Galaxy ◽  
Ionization Cross Sections

O f the nuclear cosmic rays arriving in the vicinity of Earth from interstellar space, more than 90% have energies less than 1010 eV /u.f Some effects of their modulation (including deceleration) in the Solar System are briefly discussed. The origin of particles at energies < 107 eV/u is still obscure. They could be due to stellar explosions or to solar emissions, or perhaps to interaction of interstellar gas with the solar wind. Between 108 and 1010 eV/u, the composition appears constant to ca. 30% within the statistics of available data. Cosmic rays traverse a mean path length of 6 g/cm 2 in a medium assumed to contain nine hydrogen atoms for each helium atom. Spallation reactions occurring in this medium result in enhancement of many cosmic-ray elements that are more scarce in the general abundances by several orders of magnitude. Cosmic-ray dwell time in the Galaxy seems to be < 107 years. The source composition of cosmic rays has been derived for elements with atomic numbers 1 ≤ Z ≤ 26. A comparison with abundances in the Solar System implies that the latter is richer in hydrogen and helium by a factor of ca. 20, in N and O by ca. 5, and in C by a factor of ca.2. Possible interpretations invoke (a) nucleosynthesis of cosmic rays in certain sources, e.g. supernovae, or (b) models of selective injection that depend, e.g. on ionization potentials or ionization cross sections. Calculated isotopic abundances of arriving cosmic rays are compared with the observed values now becoming available, and found to be in general agreement. Recent progress in probing the composition and spectrum of ultra-heavy nuclei is outlined.

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