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At least 883 records · Page 49
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NASA NTRS1976

Galactic cosmic ray intensity from 1 to 9 A.U

The paper is concerned with comparative observations of galactic cosmic ray intensity from 1 to 9 AU during the period April 1973-January 1976. The dominant intensity variation is found to be a coherent temporal one with a peak-to-peak amplitude of about 35% of the mean, while a further cyclic variation of about 8% peak-to-peak was found to have a 26-day period and is attributed to solar-corotating interplanetary magnetic field structures. Detailed time lag analysis of the intensity ratios for the two spacecraft yields a radial gradient of +2.0 (plus or minus 0.5) percent per AU, integral above a particle energy of 80 MeV/nucleon.

Van Allen, J. A.↗
NASA NTRS1976

The cosmic far-infrared background at high galactic latitudes

Far-infrared background fluxes from various cosmic sources are predicted. These fluxes lie near the high frequency side of the blackbody radiation spectrum. These sources could account for a significant fraction of the background radiation at frequencies above 400 GHz which might be misinterpreted as a comptonization distortion of the blackbody radiation. Particular attention is paid to the possible contributions from external galaxies, rich clusters of galaxies and from galactic dust emission.

Stecker, F. W.↗
NASA NTRS1977

SAS-2 galactic gamma-ray results. 2: Localized sources

Gamma ray emission was detected from the radio pulsars PSR 1818-04 and PSR 1747-46, in addition to the previously reported gamma ray emission from the Crab and Vela pulsars. Because the Crab pulsar is the only one observed in the optical and X-ray bands, these gamma ray observations suggest a uniquely gamma ray phenomenon occurring in a fraction of the radio pulsars. PSR 1818-04 has a gamma ray luminosity comparable to that of the Crab pulsar, whereas the luminosities of PSR 1747-46 and the Vela pulsar are approximately an order of magnitude lower. SAS-2 data for pulsar correlations yielded upper limits to gamma ray luminosity for 71 other radio pulsars. For five of the closest pulsars, upper limits for gamma ray luminosity are found to be at least three orders of magnitude lower than that of the Crab pulsar. Gamma ray enhancement near the Milky Way satellite galaxy and the galactic plane in the Cygnus region is also discussed.

Hartman, R. C.↗
NASA NTRS1977

Galactic distribution of pulsars

The density distributions of pulsars in luminosity, period, Z-distance, and galactocentric distance were derived, using a uniform sample of pulsars detected during a 408-MHz pulsar survey at Jodrell Bank. There are indications of a fine-scale structure in the spatial distributions and evidence that there is a general correlation with other galactic populations and the overall spiral structure. The electron layer in our galaxy is shown to be wider than the pulsar layer and uniform on a large scale. The number of pulsars in the galaxy has been estimated and used to derive the pulsar birthrate.

Seiradakis, J. H.↗
NASA NTRS1976

Radioactivity in the galactic plane

The paper reports the detection of a large concentration of interstellar radioactivity during balloon-altitude measurements of gamma-ray energy spectra in the band between 0.02 and 12.27 MeV from galactic and extragalactic sources. Enhanced counting rates were observed in three directions towards the plane of the Galaxy; a power-law energy spectrum is computed for one of these directions (designated B 10). A large statistical deviation from the power law in a 1.0-FWHM interval centered near 1.16 MeV is discussed, and the existence of a nuclear gamma-ray line at 1.15 MeV in B 10 is postulated. It is suggested that Ca-44, which emits gamma radiation at 1.156 MeV following the decay of radioactive Sc-44, is a likely candidate for this line, noting that Sc-44 arises from Ti-44 according to explosive models of supernova nucleosynthesis. The 1.16-MeV line flux inferred from the present data is shown to equal the predicted flux for a supernova at a distance of approximately 3 kpc and an age not exceeding about 100 years.

Walraven, G. D.↗
NASA NTRS1976

Discovery of X-ray bursts from several sources near the galactic centre

Three X-ray burst sources have been discovered within approximately 0.5 deg of the Galactic center. All bursts from this region show a low-energy cutoff near 3 keV. The bursts from MXB 1743-29 show distinct double and triple peaks; the time interval between bursts from this source was about 1.46 day. The intervals between bursts from MXB 1742-29 and MXB 1743-28 were approximately 0.55 day and 10 min respectively. Steady emission from this collection of burst sources could account for most of the flux from the apparently extended X-ray source GCX (3U 1743-29).

Lewin, W. H. G.↗
NASA NTRS1977

Interstellar ultraviolet absorption lines and galactic X-ray sources

X-ray photoionization can create zones of highly ionized trace elements in the interstellar gas around a galactic X-ray source. Ultraviolet absorption lines due to the resulting ionic column densities may be observable and may provide information on the environment and age of the X-ray source. The calculated column densities are sensitive to the rates of charge-exchange reactions.

Mccray, R.↗
NASA NTRS1977

Cosmic-ray electrons and galactic radio emission - A conflict

An analysis which takes into account the observed energy spectrum of cosmic-ray electrons above 5 GeV and calculated mean magnetic field data shows that the observed spectral index of the radio continuum in the Galaxy is in conflict with some of the cosmic-ray electron measurements. It is found that the absolute intensities of cosmic-ray electrons measured by some of the experimenters are so low that they cannot be reconciled either with the interstellar magnetic field limits or with the extent of the galactic disk toward the anticenter.

Badhwar, G. D.↗
NASA NTRS1977

5 GHz observations of galactic supernova remnants

Brightness and polarization distributions over several galactic supernova remnants have been observed at a wavelength of 6 cm. These observations have confirmed the nonthermal nature of most of the observed sources. It is suggested, however, that the objects G33.1-0.1 (KES 78), G35.6-0.0, G37.6-0.1, G37.7+0.1, and G37.9-0.4 are thermal. The results of these observations are presented in the form of total intensity contour maps with superimposed polarization vectors.

Angerhofer, P. E.↗
NASA NTRS1977

Al-26 - A galactic source of gamma-ray line emission

A detectable gamma-ray line at 1.809 MeV results from the decay of Al-26 in the interstellar medium if this isotope is synthesized in supernovae with abundance of about 0.001 relative to Mg-26. The expected intensity from the direction of the galactic center is approximately 0.0001 photon/sq cm/sec per sr, and the line width is less than 3 keV. This intensity is comparable to the intensities of the other strongest gamma-ray lines resulting from processes of nucleosynthesis at 0.847 MeV from Fe-56, 1.156 MeV from Ca-44, and 1.173 and 1.332 MeV from Ni-60. But the width of the line from Al-26 decay is an order of magnitude smaller than that of either the 0.847- or the 1.156-MeV lines, and hence this line should be much more easily observable with high-resolution detectors.

Ramaty, R.↗
NASA NTRS1977

The record of solar and galactic radiations in the ancient lunar regolith and their implications for the early history of the sun and moon

The paper reviews research into the nature and history of the lunar environment, as recorded in rocks and core samples, performed by studying effects produced by the energetic nuclear particles constituting the solar wind, solar flares, and galactic cosmic rays. Results obtained with lunar rocks are discussed which suggest a remarkable constancy of the lunar environment at least over the last several million years. Analyses of lunar core samples are examined which indicate an apparent secular change in the N-15/N-14 ratio with time in solar-wind-related nitrogen, possibly due to greatly enhanced solar flare activity in the past. Lunar and meteoritic breccias are proposed as obvious candidates for extending the radiation record much further back in time, perhaps even close to the beginning of the solar system.

Grozaz, G.↗
NASA NTRS1977

Effects of particle drifts on the solar modulation of galactic cosmic rays

Gradient and curvature drifts in an Archimedean-spiral magnetic field are shown to produce a significant effect on the modulation of galactic cosmic rays by the solar wind. The net modulation, heliocentric radial gradient, and average energy change of particles which reach the inner solar system are significantly reduced. The effects of drifts are due to the fact that cosmic rays for which the drift velocity is comparable to the wind velocity or larger, have more rapid access to the inner solar system than in the absence of drifts.

Jokipii, J. R.↗
NASA NTRS1977

CO observations of galactic reflection nebulae

Carbon monoxide emission has been observed toward about 35 galactic reflection nebulae. The peaking of CO temperatures near the hotter stars indicates substantial local heating of the gas and dust by the embedded stars. Wide low-level emission wings are seen on several of the (C-12)O line profiles; these are most plausibly interpreted as due to cloud material accelerated by such processes as radiation pressure from the newborn stars.

Knapp, G. R.↗
NASA NTRS1977

Galactic distribution of X-ray burst sources

Data on X-ray bursts recorded by the OSO-8 and SAS-3 satellites and criteria (rise time, duration, recurrence) for X-ray bursts are examined in a study of possible correlation between the galactic longitude distribution of X-ray burst sources and globular clusters. Correlations are weak, with only two X-ray bursts sources (NGC6624 and the rapid burster) coinciding with globular clusters, another seven possibly coinciding, most not correlated. Ad hoc explanations (globular clusters obscured by dust clouds, bursts associated with remnants of disrupted globular clusters evolved into supermassive black holes) are considered briefly.

Lewin, W. H. G.↗
NASA NTRS1977

The cosmic far-infrared background at high galactic latitudes

Far-infrared background fluxes from various cosmic sources are predicted. These fluxes lie near the high-frequency side of the blackbody radiation spectrum. The sources could account for a significant fraction of the background radiation at frequencies above 400 GHz, which might be misinterpreted as a 'Comptonization' distortion of the blackbody radiation. Particular attention is paid to the possible contributions from external galaxies, from rich clusters of galaxies, and from galactic dust emission.

Stecker, F. W.↗
NASA NTRS1977

The small radio source at the galactic center

Very-long-baseline interferometer observations show that the compact radio source at the Galactic Center has dimensions of approximately 200 AU and that about 25% of the emission comes from a region only 10 AU across. There is no evidence for any expansion or contraction of this compact source, with a velocity of at least a few tens of kilometers per second.

Kellermann, K. I.↗
NASA NTRS1977

Far-infrared spectrometry of H II regions and the Galactic Center

The H II regions W3, M17, and W51, as well as the Galactic center regions Sgr A and Sgr B2, were observed at a spectral resolving power of roughly 15 in the range from 45 to 115 microns. At that resolution the spectra appear featureless and can be approximated by dilute blackbody curves whose temperatures range from approximately 90 K down to about 40 K.

Ward, D. B.↗
NASA NTRS1976

A Monte-Carlo simulation of galactic cosmic ray effects in the lunar regolith

A Monte-Carlo soil mixing computer code was used to evaluate isotopic effects induced by galactic cosmic rays in samples on the top surface of the lunar regolith and in lunar core tubes. For surface samples, good agreement was found between theoretical predictions of Ne-21 concentrations, neutron fluences, and Xe-131/Xe-126 ratios, and the corresponding observations.

Langevin, Y.↗