The Explorer Program for Astronomy and Astrophysics (1986) / Chapter Skim
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ACCOMPLISHMENTS OF ASTRONOMY AND ASTROPHYSICS EXPLORERS
ACCOMPLISHMENTS OF ASTRONOMY AND ASTROPHYSICS EXPLORERS
Pages 15-24
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ISEE-3 Cosmic-Ray and Gamma-Ray Experiments 1978 FUTURE MISSIONS Dedicated Astrophysics Missio118 1. COBE Cosmic Background Explorer 1989 2.
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This measurement disproved one version of the steady state theory of cosmology whereby nucleon-antinucleon pairs were assumed to be continu ously created everywhere so as to maintain a constant density in the expanding universe.
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Cosmic noise back ground spectra measured down to 0.5 MHz provided new esti mates of the interstellar flux of cosmic rays, of magnetic fields in the galactic halo, and of the nature of radiation from distant extragalactic radio sources.
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Its orbit resulted in repeated lunar occultations of the Earth providing the welcome shielding of Earth's emissions and enabling galactic measurements to be made without interfer ence. New measurements of the nonthermal galactic radio spectrum at frequencies below 10 MHz and survey maps of the spatial distribution of the low frequency galactic emission were obtained.
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x-ray back ground provided evidence that a substantial portion originates in sources beyond the neutral hydrogen of the galactic disk and may be thermal emission from the galactic halo. With SAS-3 a Guest Observer program was initiated for Explorers.
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Studies of the data show that a significant number of nearby dwarf stars have a far infrared excess due to an extended disk or shell of solid material orbiting around and heated by the central star. This solid material is believed left over from the star formation process and represents protoplane tary material.
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The targets of IUE range from solar-system objects, such as this comet discovered by ffiAS, to active galactic nuclei and quasars. dust-to-gas ratio, and define extinction-free areas in the sky.
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These excesses indicate the pos sibility of regions of the galaxy with sizable metallicity enhancements or, alternatively, suggest a connection between cosmic ray injection and objects with peculiar surface abun dances, such as Wolf-Rayet stars. Experiments aboard the IMP satellites discovered the low energy "anomalous com ponent" of cosmic rays, now widely believed to be a population of particles accelerated from the local interstellar gas, and they demonstrated that this material does not contain the products
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IMP-6, with detectors sensi tive to the 0.1-1 MeV energy range provided the first verifica tion of the gamma-ray burst phenomenon and obtained the first spectral measurements of gamma-ray bursts. Instruments on IMP-7 measured the spectra of about 25 gamma-ray bursts and demonstrated their similarity when averaged over the burst duration.
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The focus of the mission is to study the spectrum, intensity, and isotropy of the primeval cosmic back ground radiation at wavelengths longer than that of the 3 K black body radiation maximum {at 1 mm) , and to detect or set stringent limits on the universal radiation energy density at shorter wavelengths-radiation emanating from distant sources but at later times than the primeval fireball.
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