Engineering topics

Lingenfelter, R. E.

Publications and source records attributed to Lingenfelter, R. E..

At least 73 records · Page 4

NASA NTRS1980

On the origin of the March 5, 1979 gamma ray transient: A vibrating neutron star in the Large Magellanic Cloud

It is proposed that a vibrating neutron star in the Large Magellanic Cloud is the source of the March 5 transient. Neutron star vibrations transport energy rapidly to the surface, heat the atmosphere by wave dissipation, and decay by gravitational radiation reaction. The electromagnetic emission arises from e(+)-e(-) pairs which cool and annihilate in the strong magnetic field of the neutron star. The field also confines the pairs, and this allows the production of the redshifted annihilation feature observed in the data. The redshift implies a gravitational radiation damping time which agrees with the 0.15 second duration of the impulsive phase of the event. Thus, the March 5 transient may be both the first detection of a vibrating neutron star and indirect evidence for gravitational radiation.

Ramaty, R.↗

NASA NTRS1980

Synchrotron cooling and annihilation of an E(+)-E(-) plasma: The radiation mechanism for the March 5, 1979 transient

Positron-electron pair radiation is examined as a mechanism that could be responsible for the impulsive phase emission of the March 5, 1979 transient. Synchrotron cooling and subsequent annihilation of the pairs can account for the energy spectrum, the very high brightness, and the approximately 0.4 MeV feature observed from this transient, whose source is likely to be a neutron star in the supernova remnant N49 in the Large Magellanic Cloud. In this model, the observed radiation is produced in the skin layer of a hot, radiation dominated pair atmosphere, probably confined to the vicinity of the neutron star by a strong magnetic field. The width of this layer is only about 0.1 mm. In this layer, approximately 10 to the 12th power generations of pairs are formed (by photon-photon collisions), cooled and annihilated during the approximately 0.15 sec duration of the impulsive phase. The very large burst energy implied by the distance of the Large Magellanic Cloud, and its very rapid release, are unsolved problems. Nonetheless, the possibility of neutron star vibrations, which could transport the energy coherently to the surface, heat the atmosphere mechanically to a hot, pair-producing temperature, and have a characteristic damping time roughly equal to the duration of the impulsive phase are addressed.

Ramaty, R.↗

NASA NTRS1980

Cosmic gamma-ray lines - Theory

The various processes that lead to gamma-ray line emission and the possible astrophysical sources of such emission are reviewed. The processes of nuclear excitation, radiative capture, positron annihilation, and cyclotron radiation, which may produce gamma-ray line emission from such diverse sources as the interstellar medium, novas, supernovas, pulsars, accreting compact objects, the galactic nucleus and the nuclei of active galaxies are considered. The significance of the relative intensities, widths, and frequency shifts of the lines are also discussed. Particular emphasis is placed on understanding those gamma-ray lines that have already been observed from astrophysical sources.

Lingenfelter, R. E.↗

NASA NTRS1980

Primary cosmic ray positrons and galactic annihilation radiation

The observation (Leventhal et al, 1978) of positron annihilation radiation at 0.511 MeV from the direction of the Galactic Center is reexamined, suggesting the possibility of a primary positron component of the cosmic rays. The observed 0.511 MeV emission requires a positron production rate nearly two orders of magnitude greater than the production rate of secondary cosmic ray positrons from pion decay produced in cosmic ray interactions. Possible sources of positrons are reviewed with both supernovae and pulsars appearing to be the more likely candidates. If only about 1% of these positrons were accelerated along with the cosmic ray nucleons and electrons to energies not less than 100 MeV, it is believed that these primary positrons would be comparable in intensity to those secondary positrons resulting from pion decay. Some observational evidence for the existence of primary positrons in the cosmic rays is also discussed.

Lingenfelter, R. E.↗

NASA NTRS1980

Solar particle fluxes and the ancient sun

The implications of the statistical data on solar flare particle fluxes, for the present and the ancient sun, considering modern data from the past two solar cycles, C-14 data from the past 7000 years, and Al-26 and Mn-53 data in lunar samples for the last 10-million years are reviewed. All of these records suggest that there is a maximum proton fluence (greater than 10 MeV) from a solar flare on the order of 10 to the 10th p/sq cm, above which the size-frequency distribution steepens sharply. From this it is extremely unlikely that energetic particles from solar flares could have contributed to extinction catastrophes in the fossil record.

Lingenfelter, R. E.↗

NASA NTRS1979

Nuclear gamma-rays from energetic particle interactions

Gamma-ray line emission due to nuclear deexcitation following energetic particle interactions with abundant constituents of cosmic matter is studied. Reactions induced by energetic protons and alpha particles in ambient nuclei (He, C, N, O, Ne, Mg, Al, Si, S, Ca, and Fe) are considered, along with inverse reactions in which energetic nuclei interact with ambient H and He. Line-production cross sections are evaluated by analyzing a large body of laboratory nuclear data. Both prompt gamma rays, produced by direct excitation of nuclear levels and by spallation reactions that leave the secondary nucleus in an excited state, and delayed emission from long-lived radioactive nuclei also produced in the energetic particle reactions are investigated. A line list is provided, and the shapes of the gamma-ray lines are determined. Gamma-ray line production in the interstellar medium is evaluated in detail.

Ramaty, R.↗

NASA NTRS1979

Gamma-ray line astronomy

Gamma-ray astronomy is a valuable source of information on solar activity, supernovae, and nucleosynthesis. Cosmic gamma-ray lines were first observed from solar flares and more recently from the galactic center and a transient event. The latter may give an important insight into nuclear reactions taking place near neutron stars and black holes and a measure of the gravitational redshifts of such objects.

Ramaty, R.↗

NASA NTRS1979

Astrophysical gamma-ray spectroscopy

Observations of gamma-ray lines from solar flares, the Galactic Center, and transient celestial events are reviewed. The lines observed in each case are identified, and possible emission sources are considered. Future prospects for gamma-ray line astronomy are briefly discussed.

Ramaty, R.↗

NASA NTRS1978

Nuclear gamma rays from energetic particle interactions

Gamma ray line emission from nuclear deexcitation following energetic particle reactions is evaluated. The compiled nuclear data and the calculated gamma ray spectra and intensities can be used for the study of astrophysical sites which contain large fluxes of energetic protons and nuclei. A detailed evaluation of gamma ray line production in the interstellar medium is made.

Ramaty, R.↗

NASA NTRS1978

Nuclear gamma rays from compact objects

Accreting compact objects may be important gamma ray line sources and may explain recent observations of celestial gamma-ray line emission from a transient source in the direction of the galactic anti-center, from the galactic center, and possibly from the radio galaxy Centaurus A. The identification of the lines from the transient source requires a strong redshift. Such a redshift permits the identification of these lines with the most intense nuclear emission lines expected in nature, positron annihilation, and neutron capture on hydrogen and iron. Their production as a result of nuclear interactions in accreting gas around a neutron star is proposed. The gamma-ray line emission from the galactic center and possibly Centaurus A appears to have a surprisingly high luminosity, amounting to perhaps as much as 10% of the total luminosity of these sources. Such high gamma-ray line emission efficiencies could result from nuclear interactions in accreting gas around a massive black hole.

Lingenfelter, R. E.↗

NASA NTRS1978

Gamma-ray lines - A new window to the Universe

Gamma-ray emission is considered in terms of its usefulness in determining the physics of nucleosynthesis, the interstellar medium, solar flares, supernovae, and neutron stars. The mechanism of gamma-ray line emission is reviewed, i.e., nuclear deexcitation, radiative capture, positron annihilation, and possibly cyclotron radiation in the strong magnetic fields of neutron stars. Various gamma-ray spectra, obtained from balloon and satellite data, are analyzed with attention to solar particle energies and densities, including particle emission from black-hole supernova remnants.

Lingenfelter, R. E.↗

NASA NTRS1977

Crater evolutionary tracks

The technique proposed in the present paper for studying planetary surface processes is based on the measurement of crater rim height, h, depth, d, and diameter, D. The h/d and d/D ratios provide a quantitative description of crater morphology as well as a quantitative method for assessing the relative importance of competing crater modification processes (since h, d, and D change as a crater is degraded by surface processes, and h/d and d/D change with time). Different classes of processes produce distinctive evolutionary tracks on an h/d versus d/D diagram. Tracks for three general classes of crater modification (processes adding material to the crater; processes redistributing the material within the crater vicinity; and processes removing the material from the crater vicinity) are calculated, and h/d and d/D ratios for craters on the earth, moon, and Mars are compared.

Schubert, G.↗

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

Diffuse galactic gamma ray lines

The production rate of 4.44-MeV line for a variety of assumed cosmic ray spectra is evaluated. These results are compared with reported galactic gamma-ray line intensities and are consistent with a low energy cosmic ray density which increases toward the galactic center in proportion to the molecular gas density.

Lingenfelter, R. E.↗

NASA NTRS1977

Gamma-ray lines from interstellar grains

The letter points out the existence of a hitherto unknown component of gamma-ray line emission: very narrow (FWHM less than 5 keV) lines from interstellar grains. The prime candidate for detection is the line at 6.129 MeV from O-16, but other very narrow lines could also be detected at 0.847, 1.369, 1.634, 1.779, and 2.313 MeV from Fe-56, Mg-24, Ne-20, Si-28, and N-14. Measurements of this line emission can provide information on the composition, size, and spatial distribution of interstellar grains.

Lingenfelter, R. E.↗

NASA NTRS1977

Solar wind nitrogen - Mechanisms for isotopic evolution

Isotope systematics of nitrogen implanted in the lunar regolith indicate that the N-15/N-14 ratio at the source of the nitrogen has increased substantially with time. This source is most plausibly identified as the solar wind reservoir. However, rigorous testing of possible mechanisms for isotopic evolution of the solar convective zone shows that they all fail, by large factors, to explain the observed effect. Evolutionary processes on the lunar surface may be similarly eliminated, leaving the lunar nitrogen isotope anomaly currently unexplained.

Kerridge, J. F.↗

NASA NTRS1976

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

It is shown that Al26 is a very good candidate for producing a detectable gamma-ray line, and that this line is not only intense but also very narrow. By examining the chart of nuclides for other radioactive isotopes which could produce hiterto unnoticed gamma-ray lines following nucleosynthesis, it is found that for mass numbers less than 60, the isotopes Na22, Al26, K40, Ar42, Ti44, Sc46, Mn54, Co56, Co57, Co58, Co60 and Fe60 are the only ones with sufficiently long half lives (70) days to produce gamma rays in optically thin regions.

Ramaty, R.↗

NASA NTRS1976

Gamma ray lines from interstellar grains

The existence of very narrow (FWHM or approximately = 5 KeV) gamma ray line emission from interstellar grains is pointed out. The prime candidate for detection is the line at 6.129 Mev from O-16, but other very narrow lines could also be detected at 0.847, 1.369, 1.634, 1.779 and 2.313 Mev from Fe-56, Mg-24, Ne-20, Si-28 and N-14. Measurements of this line emission can provide information on the composition, size and spatial distribution of interstellar grains.

Lingenfelter, R. E.↗