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 The COMPTEL Orion result is now attributed chiefly to an instrumental artifact, and has been withdrawn.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 What do Gamma Rays tell us about the ISM?: New Insight from the Compton Observatory

1996 ◽  
Vol 169 ◽  
pp. 437-446 ◽  
Author(s):  
Hans Bloemen
Keyword(s):  
Interstellar Medium ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Line Emission ◽  
Cosmic Ray ◽  
Gamma Ray Astronomy ◽  
Early Results ◽  
The Galaxy ◽  
Γ Ray ◽  
Insight Into

Gamma-ray astronomy has become a rich field of research and matured significantly since the launch of NASA's Compton Gamma Ray Observatory in April 1991. Studies of the diffuse γ-ray emission of the Galaxy can now be performed in far more detail and extended into the MeV regime, including both continuum and line emission. These studies provide unique insight into various aspects of the interstellar medium, in particular of the cosmic-ray component. This paper gives a brief review on the diffuse Galactic γ-ray emission and summarizes early results and prospects from the Compton Observatory.

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

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 Gamma Rays from Cosmic Rays

1981 ◽  
Vol 94 ◽  
pp. 309-319 ◽  
Author(s):  
A. W. Wolfendale
Keyword(s):  
Cosmic Rays ◽  
Gamma Rays ◽  
Molecular Clouds ◽  
Cosmic Ray ◽  
Cosmic Ray Intensity ◽  
Cosmic Ray Interactions ◽  
The Galaxy ◽  
Γ Rays ◽  
Γ Ray

It is shown that there is evidence favouring molecular clouds being sources of γ-rays, the fluxes being consistent with expectation for ambient cosmic rays interacting with the gas in the clouds for the clouds considered. An estimate is made of the fraction of the apparently diffuse γ-ray flux which comes from cosmic ray interactions in the I.S.M. as distinct from unresolved discrete sources. Finally, an examination is made of the possibility of gradients of cosmic ray intensity in the Galaxy.

scholarly journals High-energy Galactic phenomena and the interstellar medium

1985 ◽  
Vol 106 ◽  
pp. 225-233
Author(s):  
Catherine J. Cesarsky
Keyword(s):  
Magnetic Fields ◽  
Interstellar Medium ◽  
Molecular Hydrogen ◽  
Gamma Ray ◽  
Cosmic Ray ◽  
High Energy ◽  
Small Scale ◽  
The Galaxy ◽  
Γ Rays ◽  
Γ Ray

Gamma rays of energy in the range 30 MeV-several GeV, observed by the satellites SAS-2 and COS-B, are emitted in the interstellar medium as a result of interactions with gas of cosmic-ray nuclei in the GeV range (π° decay γ rays) and cosmic-ray electrons of energy > 30 MeV (bremsstrahlung γ rays). W. Hermsen has presented at this conference the γ ray maps of the Galaxy in three “colours” constructed by the COS-B collaboration; the information in such maps is supplemented by radio-continuum studies (see lecture by R. Beck), and is a useful tool for studying the distribution of gas, cosmic rays (c.r.) and magnetic fields in the Galaxy. The variables in this problem are many:large-scale (~ 1 kpc) and small-scale (~10 pc) distributions of c.r. nuclei, of c.r. electrons, of atomic and molecular hydrogen, of magnetic fields, fraction of the observed radiation due to localized sources, etc. Of these, only the distribution - or at least the column densities - of atomic hydrogen are determined in a reliable way. Estimates of the amount of molecular hydrogen can be derived from CO observations or from galaxy counts. The radio and gamma-ray data are not sufficient to disentangle all the other variables in a unique fashion, unless a number of assumptions are made (e.g. Paul et al. 1976). Still, the COS-B team has been able to show that :a) there is a correlation between the gamma-ray emission from local regions, as observed at intermediate latitudes, and the total column density of dust, as measured by galaxy counts. The simplest interpretation is that the density of c.r. nuclei and electrons is uniform within 500 pc of the sun, and that dust and gas are well mixed. Then, γ rays can be used as excellent tracers of local gas complexes (Lebrun et al. 1982, Strong et al. 1982).b) In the same way, the simplest interpretation of the γ-ray emission at energy > 300 MeV from the inner Galaxy, is that c.r. nuclei and electrons are distributed uniformly as well : there is no need for an enhanced density of c.r. in the 3–6 kpc ring; on the contrary, even assuming a uniform density of c.r., the γ-ray data are in conflict with the highest estimates of molecular hydrogen in the radio-astronomy literature (Mayer-Hasselwander et al. 1982).c) In the outer Galaxy, the gradient of c.r. which had become apparent in the early SAS-2 data can now, with COS-B data, be studied in three energy ranges. A gradient in the c.r. distribution is only required to explain the low-energy radiation, which is dominated by bremsstrahlung from relativistic electrons (Bloemen et al., in preparation).

scholarly journals Measuring Cosmic Elements with Gamma-Ray Telescopes

2009 ◽  
Vol 26 (3) ◽  
pp. 359-364
Author(s):  
Roland Diehl
Keyword(s):  
Positron Annihilation ◽  
Massive Star ◽  
Gamma Ray ◽  
Nuclear Astrophysics ◽  
The Galaxy ◽  
Bulge Region ◽  
Γ Ray ◽  
Cas A ◽  
Gamma Ray Telescopes ◽  
Radioactive Trace

AbstractGamma-ray telescopes are capable of measuring radioactive trace isotopes from cosmic nucleosynthesis events. Such measurements address new isotope production rather directly for a few key isotopes such as 44Ti, 26Al, 60Fe, and 56Ni, as well as positrons from the β+-decay variety. Experiments of the past decades have now established an astronomy with γ-ray lines, which is an important part of the study of nucleosynthesis environments in cosmic sources. For massive stars and supernovae, important constraints have been set: Co isotope decays in SN1987A directly demonstrated the synthesis of new isotopes in core-collapse supernovae, 44Ti from the 340-year-old Cas A supernova supports the concept of α-rich freeze-out, but results in interesting puzzles pursued by theoretical studies and future experiments. 26Al and 60Fe has been measured from superimposed nucleosynthesis within our Galaxy, and sets constraints on massive-star interior structure through its intensity ratio of ∼15%. The 26Al γ-ray line is now seen to trace current star formation and even the kinematics of interstellar medium throughout the Galaxy. Positron annihilation emission from nucleosynthesis throughout the plane of our Galaxy appears to be mainly from 26Al and other supernova radioactivity, but the striking brightness of the Galaxy's bulge region in positron annihilation γ-rays presents a puzzle involving several astrophysics issues beyond nuclear astrophysics. This paper focuses mainly on a discussion of 26Al and 60Fe from massive-star nucleosynthesis.

scholarly journals Evolutionary Models of Nucleosynthesis in the Galaxy

1971 ◽  
Vol 10 ◽  
pp. 179-222
Author(s):  
J. W. Truran ◽  
A.G.W. Cameron
Keyword(s):  
Black Hole ◽  
Star Formation ◽  
Massive Star ◽  
Massive Stars ◽  
Cosmic Ray ◽  
Heavy Elements ◽  
Core Material ◽  
Massive Star Formation ◽  
The Core ◽  
The Galaxy

AbstractA model of the galaxy is constructed and evolved in which the integrated influence of stellar and supernova nucleosynthesis on the composition of the interstellar gas is traced numerically. Our detailed assumptions concerning the character of the matter released from evolving stars and supernovae are guided by the results of recent stellar evolutionary calculations and hydrodynamic studies of supernova events. Stars of main sequence mass in the range 4 ≤ M ≤ 8 M⊙ are assumed to give rise to supernova events, leaving remnants we identify with neutron stars and pulsars and forming both the carbon-to-iron nuclei and the r-process heavy elements in the explosive ejection of the core material. For more massive stars, we assume the core implosion will result in the formation of a Schwarzschild singularity, that is, a black hole or ‘collapsar’. The straightforward assumptions (1) that the gas content of the galaxy decreases exponentially with time to its present level of ~ 5 % and (2) that the luminosity function characteristic of young clusters and the solar neighborhood is appropriate throughout galactic history, lead to the prediction that ≈ 20% of the unevolved stars of approximately one solar mass (M⊙) in the galaxy today should have metal compositions Z ≲ 0.1 Z⊙. As Schmidt has argued from similar reasoning, this is quite inconsistent with current observations; an early generation dominated by more massive stars – which would by now have evolved – is suggested by this difficulty. Many of these massive stars, according to our assumptions, will end their lives as collapsed black hole remnants. It is difficult to visualize an epoch of massive star formation in the collapsing gas cloud which formed our galaxy which would enrich the gas rapidly enough to account for the level of heavy element abundances in halo population stars; we have therefore proposed a stage of star formation which is entirely pregalactic in character. We suggest that the Jeans’ length-sized initial condensations in the expanding universe discussed by Peebles and Dicke may provide the appropriate setting for this first generation of stars. Guided by these considerations, and by the need for a substantial quantity of ‘unseen’ mass to bind our local group of galaxies, we have constructed a model of the galaxy in which this violent early phase of massive star formation produces both (1) approximately 25 % of the level of heavy elements observed in the solar system and (2) an enormous unseen mass in the form of black holes. The implications of our model for other features of the galaxy, including supernova nucleosynthesis, the cosmic ray production of the light elements, and cosmochronology, are discussed in detail.

scholarly journals Gamma-Ray Imaging of the Galactic Center Region

1989 ◽  
Vol 136 ◽  
pp. 581-585
Author(s):  
W. R. Cook ◽  
D. M. Palmer ◽  
T. A. Prince ◽  
S. M. Schindler ◽  
C. H. Starr ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Galactic Center ◽  
Coded Aperture ◽  
Center Region ◽  
Gamma Ray Imaging ◽  
The Galaxy ◽  
Γ Ray ◽  
Luminous Objects

The Caltech imaging γ-ray telescope was launched by balloon from Alice Springs, NT, Australia and performed observations of the galactic center during the period 12.62 to 13.00 April 1988 UT. The first coded-aperture images of the galactic center region at energies above 30 keV show a single strong γ-ray source which is located 0.7±0.1° from the galactic nucleus and is tentatively identified as 1E1740.7-2942. If the source is at the distance of the galactic center, it is one of the most luminous objects in the galaxy at energies from 35 to 200 keV.

scholarly journals Molecular Clouds Observed by the EGRET Gamma-Ray Telescope

1997 ◽  
Vol 170 ◽  
pp. 22-24 ◽  
Author(s):  
Seth. W. Digel ◽  
Stanley D. Hunter ◽  
Reshmi Mukherjee ◽  
Eugéne J. de Geus ◽  
Isabelle A. Grenier ◽  
...  
Keyword(s):  
Molecular Mass ◽  
Molecular Clouds ◽  
Gamma Ray ◽  
Angular Resolution ◽  
Cosmic Ray ◽  
High Energy ◽  
Background Rejection ◽  
Γ Rays ◽  
Γ Ray ◽  
Production Mechanisms

EGRET, the high-energy γ-ray telescope on the Compton Gamma-Ray Observatory, has the sensitivity, angular resolution, and background rejection necessary to study diffuse γ-ray emission from the interstellar medium (ISM). High-energy γ rays produced in cosmic-ray (CR) interactions in the ISM can be used to determine the CR density and calibrate the CO line as a tracer of molecular mass. Dominant production mechanisms for γ rays of energies ∼30 MeV–30 GeV are the decay of pions produced in collisions of CR protons with ambient matter and Bremsstrahlung scattering of CR electrons.

Sign in / Sign up

Export Citation Format

Share Document