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At least 1,063 records · Page 59
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NASA NTRS1973

SAS-2 observations of gamma rays from the galactic plane

The SAS-2 gamma ray experiment has made measurements on the high energy gamma rays coming from the galactic center region. The gamma radiation in this region is very much more intense than in the anticenter region, in agreement with the observations made with the OSO-3 experiment of Kraushaar et al. (1973); and exhibits a narrow distribution along the plane which is nearly uniform in intensity from 330 deg to 30 deg. The energy spectrum in the range from 35 MeV to 210 MeV is quite flat, consistent with a cosmic ray-interstellar matter interaction pion-decay spectrum, or a mixture of this spectrum and a spectrum formed by Compton radiation from cosmic ray electrons. The intensity of the radiation in the anticenter direction is consistent with that expected from the cosmic ray-interstellar matter interaction origin, namely 0.000.002 photons.

Kniffen, D. A.↗
NASA NTRS1972

Modulation of low-energy galactic cosmic rays over solar maximum /cycle 20/.

Low-energy (about 60 MeV/nucleon) galactic cosmic rays observed during the recent period of solar maximum are reviewed. For this particular cycle, a significant time lag between intensity changes in the low-energy and high-energy components has been observed. Several possible explanations of this 'hysteresis effect' are discussed. The cosmic-ray intensity gradients provided by Pioneer 10 are soon to be available and are expected to provide a more definite clue to this process of cosmic-ray modulation.

Van Hollebeke, M. A. I.↗
NASA NTRS1972

Nuclear gamma rays from Li-7 in the galactic cosmic radiation.

The observation of a gamma-ray line feature from the direction of the galactic center by Johnson, Harnden, and Haymes is interpreted as the 478-keV nuclear de-excitation of low-energy Li-7 cosmic rays as they inelastically scatter from the interstellar gas. The prediction of an associated line at 432 keV is proposed as a definitive test of this idea.

Fishman, G. J.↗
NASA NTRS1972

Solar flare and galactic cosmic ray studies of Apollo 14 and 15 samples.

Thermoluminescence (TL) measurements in rock 14310 show a strong depth dependence consistent with that expected from solar flares. This effect should prove useful in studying solar flare fluctuations in the time interval of 100 to 100,000 years. Rare gas spallation ages for rock 14301, 14306, and 14311 are respectively 102 plus or minus 30, 25 plus or minus 2, and 661 plus or minus 72 m.y. The 14306 value supports the idea that Cone Crater was formed 25 million years ago. Groupings of exposure ages suggest the dates of other major cratering events. Galactic track data in 14310 show little depth dependence.

Crozaz, G.↗
NASA NTRS1973

Preliminary Pioneer-10 intensity gradients of galactic cosmic rays.

Selected data from the University of Chicago charged-particle telescope on the Pioneer-10 spacecraft bound for Jupiter have been examined and compared with data from the University of Chicago charged-particle telescopes on the Earth satellites IMP-5 and IMP-6 at 1 AU to derive a preliminary integral intensity gradient for relativistic galactic protons and helium nuclei. The preliminary value obtained is (4.5 plus or minus 1.0) percent per AU over the radial range 1-2.8 AU. Preliminary differential gradients also have been obtained for the energy range 29-67 MeV per nucleon.

Mckibben, R. B.↗
NASA NTRS1973

Calculations of neutron flux spectra induced in the earth's atmosphere by galactic cosmic rays.

Calculations have been carried out to determine the neutron flux induced in the earth's atmosphere by galactic protons and alpha particles at solar minimum for a geomagnetic latitude of 42 N. Neutron flux spectra in the energy range from about 10 to the minus 8th to about 100,000 MeV at various depths in the atmosphere were calculated by using Monte Carlo and discrete ordinates methods, and various comparisons with experimental data are presented. The magnitude and shape of the calculated neutron leakage spectrum at the particular latitude considered support the theory that the cosmic ray albedo neutron decay (Crand) mechanism is the source of the protons trapped in the inner radiation belt.

Armstrong, T. W.↗
NASA NTRS1973

Far-infrared observations of galactic nuclei.

M82 (NGC 3034) and NGC 253 have been detected at wavelengths from 27 to 125 microns by using a 30-cm airborne IR telescope and a multiband photometer. Spectral power distribution curves are plotted for the galactic nuclei. Tables of obtained data are also given.

Harper, D. A., Jr.↗
NASA NTRS1973

A stochastic model of the galactic magnetic field.

Existing stochastic models of the galactic magnetic field are considered and found to suffer certain defects. A new model is proposed which overcomes faults of the previous theories while retaining their strenghts.

Kaiser, T. B.↗
NASA NTRS1973

The generation and dissipation of solar and galactic magnetic fields.

Turbulent diffusion of magnetic field plays an essential role in the generation of magnetic field in most astrophysical bodies. Review of what can be proved and what can be believed about the turbulent diffusion of magnetic field. Observations indicate the dissipation of magnetic field at rates that can be understood only in terms of turbulent diffusion. Theory shows that a large-scale weak magnetic field diffuses in a turbulent flow in the same way that smoke is mixed throughout the fluid by the turbulence. The small-scale fields (produced from the large-scale field by the turbulence) are limited in their growth by reconnection of field lines at neutral points, so that the turbulent mixing of field and fluid is not halted by them. Altogether, it appears that the mixing of field and fluid in the observed turbulent motions in the sun and in the Galaxy is unavoidable. Turbulent diffusion causes decay of the general solar fields in a decade or so, and of the galactic field in 100 m.y. to 1 b.y. It is concluded that continual dynamo action is implied by the observed existence of the fields.

Parker, E. N.↗
NASA NTRS1973

Motions near the galactic center and the '3-kpc arm.'

As a first approximation, the motions of the neutral hydrogen in the region between 1 and 5 kpc from the galactic center are found to be well represented in the Tb(l, V) diagram by a disk in differential rotation, and no evidence is found for a general field of expanding motions. Consequently, a rotation curve for this region has been derived from the observations. The new curve indicates a more uniform distribution of mass in the inner region of the Galaxy than many previous models. In a second approximation, a set of parameters is derived for an elliptical dispersion ring that represents not only the 3-kpc arm but also the + 70 km/sec expanding arm in the Tb(l, V) diagram.

Simonson, S. C., III↗
NASA NTRS1973

Investigation of gamma rays from the galactic center

Data from Argentine balloon flights made to investigate gamma ray emission from the galactic center are summarized. Data are also summarized from a Palestine, Texas balloon flight to measure gamma rays from NP 0532 and Crab Nebulae.

Helmken, H. F.↗
NASA NTRS1973

The 'rolling motion' phenomenon in galactic spiral arms

The 'rolling motion' in the spiral arms in the outer parts of the Galaxy are interpreted as only apparent motions caused by the combined effect of the bending of the galactic plane and the differential rotation. Theoretical contour maps (latitude vs velocity) are plotted in a number of directions on both sides of the Galaxy for direct comparison with observations. The velocity and density fields used in the calculations are based on a linear analysis of the three-dimensional gas motions in response to the spiral density-wave potential studied by Lin, Shu, and Yuan and by Vandervoort (1970). It is found that the combined effect under consideration is sufficient to cause an apparent rolling motion in a spiral arm.

Yuan, C.↗
NASA NTRS1973

The galactic space frequency of close binary systems

An investigation of the galactic space frequency of close binary systems and other stars with high angular momentum is made on the basis of several criteria for the binary nature of a star. Within an accessible range of 3 kpc around the sun, which includes parts of three spiral arms, there occurs no significant variation (to within a factor of about 2) in the space frequencies of B-type radial-velocity variables, M-type supergiants with blue companions, and Be stars. Implications of this result for the problems of the origin of close binary systems, the distribution of angular momentum in the Galaxy, and the relative numbers of blue and red supergiants are discussed.

Stothers, R.↗
NASA NTRS1974

On the nature of the nonthermal radio emission from the galactic center

Some recent observations of the galactic center appear at first sight to have made the character of the radio source Sgr A unclear. The flatness of the usually quoted spectrum, the lack of any measured polarization, the presence of hydrogen recombination lines, and the radio-infrared luminosity ratio are all consistent with Sgr A being a rather hot H II region. It is shown here, however, that when flux measurements between 80 MHz and 91000 MHz are all included and the multiple nature of the source is accounted for, the spectral index exceeds 0.4 - much too steep to be bremsstrahlung. There is, therefore, no question that Sgr A is a nonthermal source. It is further argued on the basis of a comparison of appearance, energetics and the recent results which no longer put Sgr A exactly at the center of the galaxy that Sgr A could be a supernova remnant rather than a miniature of active extragalactic radio sources.

Jones, T. W.↗
NASA NTRS1974

Galactic heavy cosmic rays with 5 less than E less than 130 MeV/nucleon

With stacks of Lexan and cellulose triacetate exposed outside the lunar modules on Apollo 16 and 17, a study was made of the spectra and composition of low-energy particles in interplanetary space. For the period from Apr. 16 to 23, 1972 (Apollo 16), measurements were made of the spectra of the elements 6 less than or equal to Z less than or equal to 28 at energies 40 less than or equal to E less than or equal to 150 MeV/nucleon. For the period from Dec. 11 to 13, 1972 (Apollo 17), a study was made of CNO, NeMgSi, and elements with Z greater than 16 at energies 5 less than or equal to E less than or equal to 40 MeV/nucleon. Using the abundance of charges 17 less than or equal to Z less than or equal to 25 relative to iron as a tracer, it is found that the bulk of the heavy particles in interplanetary space at E greater than 10 MeV/nucleon are of galactic rather than solar origin. The relative abundances of the various charge groups are independent of energy from about 2 GeV/nucleon down to about 30 MeV/nucleon.

Price, P. B.↗
NASA NTRS1974

Abundances relative to carbon of the elements silicon to nickel in the galactic cosmic radiation

Discussion of the abundances relative to carbon of the elements from silicon to nickel in the galactic cosmic radiation as measured by cosmic ray telescopes on the IMP-5 and IMP-7 satellites, in energy ranges between 40 and 450 MeV/nucleon depending on the species. The IMP-7 measurements are still to be considered only preliminary and do not yet fully exploit the resolution capabilities of that instrument. Calculations of the abundances to be expected in this charge range if the cosmic radiation traverses 6 g/sq cm of material after acceleration are presented, and the consequences which follow both for propagation models and for the chemical composition of the sources of the cosmic radiation are discussed.

Cartwright, B.↗
NASA NTRS1974

The modulation of low energy galactic cosmic rays

It has been clearly established by several different experiments that following the last solar maximum (about 1969), there was a significant phase lag or hysteresis effect between changes in the low rigidity galactic cosmic rays and the high rigidity components. It was possible to explain this in terms of the diffusion-convection-modulation theory by varying either the diffusion coefficient or the size of the modulation region as a function of time. During the ensuing recovery phase of the solar modulated spectra, at the mid point toward the minimum of the solar activity, new striking features have been observed, and these new observations are discussed.

Van Hollebeke, M. A. I.↗