Astronomy and Astrophysics for the 1980's, Volume 2 Reports of the Panels (1983) / Chapter Skim
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VI. Gamma-Ray Astronomy
VI. Gamma-Ray Astronomy
Pages 43-54
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From page 43... ...
It was recognized that interactions of cosmic rays with interstellar matter and starlight must produce photons in the gamma
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From page 44... ...
Measurements of the diffuse component of Galactic gamma rays provided information on the distribution of cosmic rays in the Galaxy and demonstrated the feasibility of obtaining a high-contrast picture of this important aspect of Galactic structure from future observations that will be made with improved sensitivity and angular resolution. The spectrum of the diffuse component of extragalactic gamma rays was measured over the energy range from one to several hundred MeV by instruments on Apollo 15, Apollo 17, and SAS-2.
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From page 45... ...
Observations by HEAD-3 have shown that this line emission varies and therefore must originate in a comparatively small region. Line features in the energy range from 20 to 100 keV, which are believed to be due to cyclotron resonance of electrons in magnetic fields of more than 1012 gauss, were detected in the spectra of two x-ray pulsars with scintillation spectrometers flown on balloons and on HEAD-1.
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From page 46... ...
Alternatively, it may be a nearby object of much lower peak luminosity whose direction coincides by chance with N49. Evidence of red-shifted annihilation lines and cyclotron resonance features has been found on the gamma-ray spectra of several other bursts by scintillation detectors on Soviet spacecraft.
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From page 47... ...
During the early part of the decade, observations in the energy range from 0.1 to 10 MeV were made primarily with actively shielded sodium iodide scintillation detectors. Solidstate spectrometers with cryogenically cooled germanium crystals, which afforded spectral resolutions 20 to 30 times better than scintillation counters, were developed for various balloon and space instruments, and in 1979 several large detectors were launched aboard HEAD-3.
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From page 48... ...
Measure the cyclotron resonance lines in the spectra of x-ray pulsars and the nuclear lines and positron annihilation lines in the spectra of gamma-ray bursts and transients to obtain information about magnetic-field intensities, gravitational red shifts, surface compositions, and the processes of particle acceleration in the vicinity of neutron stars and other compact objects. Search for sources of gamma rays with the unique characteristics expected from black holes, such as very short bursts signaling the final evaporation events of small black holes.
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From page 49... ...
Extend the observations of these comparatively rare events into the x-ray and possibly other regions of the spectrum. New and powerful approaches to the study of the nature of gamma-ray bursts have been opened by the detection of spectral features identified with the positron annihilation line red shifted to about 400 keV and with cyclotron resonance of electrons in magnetic fields greater than 1012 gauss.
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From page 50... ...
resources for gamma-ray astronomy consist of a number of balloonborne instruments and several small gamma-ray burst detectors carried on the Vela satellites SB, 6A, and 6B, on the ISEE-3 satellite, and on the Pioneer Venus Orbiter. The European COS-B satellite, carrying a spark chamber telescope for highenergy gamma rays, continues to return valuable data.
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From page 51... ...
The payload of the GRO, as currently planned, consists of gamma-ray telescopes for observations in the energy range from several times 104 eV to about 2 X 101° eV, including observations of gamma-ray bursts and spectroscopy of gamma-ray emission lines. The sensitivities of the GRO instruments will surpass those of previous detectors by at least one order of magnitude over the entire spectral range, and their angular resolutions will be substantially better.
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From page 52... ...
The 0.511-MeV line and cyclotron resonance lines from x-ray pulsars, which can be detected by several of the existing balloonborne detectors, will be studied in much finer detail by the GRO instruments. The spectrometers on the GRO will be used in a sensitive search for nucleosynthetic gamma-ray lines from young Galactic and nearby extragalactic supernova remnants, as well as from long-lived radioactive debris in interstellar space.
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From page 53... ...
They will obtain detailed information on the spatial uniformity and energy spectrum of extragalactic diffuse radiation, which is needed to determine the origin of this radiation. m ese telescopes are also expected to measure detailed properties of galactic diffuse radiation in sufficient detail to determine the distribution of cosmic rays in the Galaxy, to ascertain the role of molecular clouds in holding cosmic rays in the Galaxy, and to see elements of Galactic structure clearly.
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From page 54... ...
2. Advanced Gamma-RaY Experiments Following the GRO mission, there will be a need to carry out high-energy gamma-ray observations with sufficient sensitivity and angular resolution to define detailed spatial features of emission regions such as molecular clouds, Galactic arms, and nearby galaxies and to measure complex variations of compact sources.
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