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At least 1,333 records · Page 74
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NASA NTRS1986

Double layers and circuits in astrophysics

A simple circuit is applied to the energizing of auroral particles, to solar flares, and to intergalactic double radio sources. Application to the heliospheric current systems leads to the prediction of two double layers on the Sun's axis which may give radiations detectable from Earth. Double layers in space should be classified as a new type of celestial object. It is suggested that X-ray and gamma-ray bursts may be due to exploding double layers (although annihilation is an alternative energy source). The way the most used textbooks in astrophysics treat concepts like double layers, critical velocity, pinch effects and circuits was studied. It is found that students using these textbooks remain essentially ignorant of even the existence of these, although some of the phenomena were discovered 50 yr ago.

Alfven, H.↗
NASA NTRS1986

Astronomy on a manned Mars mission

Three extra-solar-system astronomical experiments onboard a manned Mars mission are proposed. First, a modest, 50 cm aperture optical-ultraviolet-infrared telescope (or pair used as an interferometer) coupled with the Mars-Sun baseline would increase the number (by a factor of 3.4) and a volume of stars with accurately measured distances via stellar parallax and, therefore, greatly improve upon the cosmic distance scale; the darker sky at Mars would also provide nearly a full astronomical magnitude deeper images of distant and low brightness objects (limited by zodiacal light). Second, a gamma-ray burst detector coupled with similar detectors in other parts of the solar system will be used to reduce the position error boxes and to study the nature of these energetic sources. Third, the long baselines on a Mars mission radio interferometer will provide a view of the radio universe at unprescedented resolution, 4 x 10 to the minus 9th arcsec at 1 mm wavelength, which can potentially resolve the engine in nearby active galaxies. Each of these experiments is relatively inexpensive, taking advantage of the human presence for operation and maintenance, and the long Earth to Mars baseline.

Burns, Jack O.↗
NASA NTRS1986

Double layers and circuits in astrophysics

As the rate of energy release in a double layer with voltage delta V is P approx I delta V, a double layer must be treated as a part of a circuit which delivers the current I. As neither double layer nor circuit can be derived from magnetofluid models of a plasma, such models are useless for treating energy transfer by means of double layers. They must be replaced by particle models and circuit theory. A simple circuit is suggested which is applied to the energizing of auroral particles, to solar flares, and to intergalactic double radio sources. Application to the heliospheric current systems leads to the prediction of two double layers on the Sun's axis which may give radiations detectable from Earth. Double layers in space should be classified as a new type of celestial object (one example is the double radio sources). It is tentatively suggested in X-ray and Gamma-ray bursts may be due to exploding double layers (although annihilation is an alternative energy source). A study of how a number of the most used textbooks in astrophysics treat important concepts like double layers, critical velocity, pinch effects and circuits is made.

Alfven, Hannes↗
NASA NTRS1987

Double Layers in Astrophysics

Topics addressed include: laboratory double layers; ion-acoustic double layers; pumping potential wells; ion phase-space vortices; weak double layers; electric fields and double layers in plasmas; auroral double layers; double layer formation in a plasma; beamed emission from gamma-ray burst source; double layers and extragalactic jets; and electric potential between plasma sheet clouds.

Williams, Alton C.↗
NASA NTRS1986

Gamma-ray bursters at cosmological distances

It is proposed that some, perhaps most, gamma-ray bursters are at cosmological distances, like quasars, with a redshift of about 1 or 2. This proposition requires a release of supernova-like energy of about 10 to the 51st ergs within less than 1 s, making gamma-ray bursters the brightest objects known in the universe, many orders of magnitude brighter than any quasars. This power must drive a highly relativistic outflow of electron-positron plasma and radiation from the source. It is proposed that three gamma-ray bursts, all with identical spectra, detected from B1900 + 14 by Mazets, Golenetskii, and Gur'yan and reported in 1979, were all due to a single event multiply imaged by a gravitational lens. The time intervals between the successive bursts, 10 hr to 3 days, were due to differences in the light travel time for different images.

Paczynski, B.↗
NASA NTRS1986

Double layers and circuits in astrophysics

A simple circuit is applied to the energizing of auroral particles, to solar flares, and to intergalactic double radio sources. Application to the heliospheric current systems leads to the prediction of two double layers on the Sun's axis which may give radiations detectable from earth. Double layers in space should be classified as a new type of celestial object. It is suggested that X-ray and gamma-ray bursts may be due to exploding double layers (although annihilation is an alternative energy source). The way the most used textbooks in astrophysics treat concepts like double layers, critical velocity, pinch effects and circuits was studied. It is found that students using these textbooks remain essentially ignorant of even the existence of these, although some of the phenomena were discovered 50 yr ago.

Alfven, Hannes↗
NASA NTRS1986

Cosmic gamma-ray lines

Recent observations of gamma-ray line emissions from gamma-ray bursts, the ISM, the Galactic center, and solar flares are reviewed, and the implications of these observations for high-energy processes in these sources are discussed. Line observations suggest that magnetized neutron stars are probably the best candidate objects for burst sources. Observations of the 1.809-MeV line from Al-26 decay provide evidence for ongoing nucleosynthesis in the Galaxy and information on the spatial distribution of nucleosynthetic sites. The compact 0.511-MeV line source is probably a black hole at or close to the Galactic center. Solar-flare studies have provided new information on the confinement and escape of charged particles at the sun and on multiple acceleration phases in solar flares.

Ramaty, R.↗
NASA NTRS1986

Results of a search for a new class of GRBS in the SMM data

The results of a search for the soft and short Gamma-Ray Bursts (GRBs) in the data of the Hard X-Ray Burst Spectrometer (HXRBS) on the Solar Maximum Mission (SMM) are presented. Data for four events are presented, including their time profiles and spectral characteristics. In one case the instrument time resolution reveals a total burst duration of 55 ms with rise and decay times of less than about 5 ms.

Kouveliotou, C.↗
NASA NTRS1987

Quantum synchrotron spectra from semirelativistic electrons in teragauss magnetic fields

Synchrotron spectra are calculated from quantum electrodynamic transition rates for thermal and power-law electron distributions. It is shown that quantum effects appear in thermal spectra when the photon energy is greater than the electron temperature, and in power-law spectra when the electron energy in units of the electron rest mass times the magnetic field strength in units of the critical field strength is of order unity. These spectra are compared with spectra calculated from the ultrarelativistic approximation for synchrotron emission. It is found that the approximation for the power-law spectra is good, and the approximation for thermal spectra produces the shape of the spectrum accurately but fails to give the correct normalization. Single photon pair creation masks the quantum effects for power-law distributions, so only modifications to thermal spectra are important for gamma-ray bursts.

Brainerd, J. J.↗
NASA NTRS1988

'Tertiary' nuclear burning - Neutron star deflagration?

A motivation is presented for the idea that dense nuclear matter can burn to a new class of stable particles. One of several possibilities is an 'octet' particle which is the 16 baryon extension of alpha particle, but now composed of a pair of each of the two nucleons, (3Sigma, Delta, and 2Xi). Such 'tertiary' nuclear burning (here 'primary' is H-He and 'secondary' is He-Fe) may lead to neutron star explosions rather than collapse to a black hole, analogous to some Type I supernovae models wherein accreting white dwarfs are pushed over the Chandrasekhar mass limit but explode rather than collapse to form neutron stars. Such explosions could possibly give gamma-ray bursts and power quasars, with efficient particle acceleration in the resultant relativistic shocks. The new stable particles themselves could possibly be the sought-after weakly interacting, massive particles (WIMPs) or 'dark' matter.

Michel, F. Curtis↗
NASA NTRS1988

On the formation of black holes

The paper explores the consequences of the existence of a burning process beyond ordinary nuclear processes (which stop at iron), involving the 'strange' particles. In effect, this idea has already had considerable discussion within the high energy physics community in terms of 'quark' matter. A possible consequence is that neutron stars may explode rather than collapse to black holes. It should be evident that such a possibility suggests radically new scenarios for activity in galactic nuclei and gamma ray burst sources.

Michel, F. Curtis↗
NASA NTRS1989

High-energy gamma-ray absorption in relativistic magnetospheres

Calculations are made of the propagation of gamma-rays around neutron stars with a dipole magnetic field, including the effects of general relativity and the absorption by the one-photon magnetic pair production process, as a model for the high-energy transport in gamma-ray burst sources and pulsars. The paper discusses the escaping photon beam characteristics as seen by distant observers at different angles with respect to the magnetic axis, for radiation arising from the polar caps of neutron stars of varying degrees of compactness and surface field strengths. The observed beaming depends strongly on the surface field only up to B of about 0.05 times the critical field value, being essentially constant above the value 0.1. The gravitational light bending contributes significantly to broaden the beam profiles especially at low energies above threshold, being sensitive to the stellar radius to mass ratio.

Riffert, H.↗
NASA NTRS1989

Man-made transients observed by the gamma-ray spectrometer on the Solar Maximum Mission satellite

Since launch in early 1980 the gamma-ray spectrometer (GRS) on SMM has monitored the sun at gamma-ray energies. In addition to observations of solar flares, cosmic gamma-ray bursts, and precipitating radiation-belt electrons, the instrument has detected a new class of high-energy transient events that cannot be attributed to any of these phenomena. The duration of these transients can range from 1 sec to more than 10 min. The average event rate between 1980 and 1986 was about five per month. However, in February 1987 this rate increased by more than a factor of 25 and continued at this high level until June 1988. These transients can be subdivided into three classes: 511-keV annihilation-line events, particle events, and broad-band photon continuumlike events. It is found that the most likely sources of these events are reactors in earth-orbiting satellites.

Rieger, Erich↗
NASA NTRS1989

Observation of nuclear reactors on satellites with a balloon-borne gamma-ray telescope

Four Soviet nuclear-powered satellites flying over a double Compton gamma-ray telescope resulted in the detection of gamma rays with 0.3-8.0 MeV energies on April 15, 1988, as the balloonborne telescope searched, from a 35-km altitude, for celestial gamma-ray sources. The satellites included Cosmos 1900 and 1932. The USSR is the only nation currently employing moderated nuclear reactors for satellite power; reactors in space may cause significant problems for gamma-ray astronomy by increasing backgrounds, especially in the case of gamma-ray bursts.

O'Neill, Terrence J.↗
NASA NTRS1988

21st century astronomical observatories on the moon

The advantages and disadvantages of building astronomical observatories on the moon are described. Several modest facilities that could be placed near an early lunar base are described, such as a 1-m optical telescope and a gamma-ray burst detector. Several more elaborate observatories are discussed, such as a lunar far-side very low frequency array, an optical interferometer, and a moon-earth ultralong baseline radio interferometer.

Burns, Jack O.↗
NASA NTRS1989

Does mass accretion lead to field decay in neutron stars

The recent discovery of cyclotron lines from gamma-ray bursts indicates that the strong magnetic fields of isolated neutron stars might not decay. The possible inverse correlation between the strength of the magnetic field and the mass accreted by the neutron star suggests that mass accretion itself may lead to the decay of the magnetic field. The spin and magnetic field evolution of the neutron star was calculated under the hypothesis of the accretion-induced field decay. It is shown that the calculated results are consistent with the observations of binary and millisecond radio pulsars.

Shibazaki, N.↗
NASA NTRS1989

Particle dynamics and gamma-ray emission in the magnetospheres of neutron stars with accretion disks

Whether the existence of cold accretion disks around isolated, magnetized neutron stars might result in a distinct observational signature due to the Compton drag interaction between the electrostatically accelerated changes and the thermal radiation emitted by these disks. The particle dynamics resulting from the combined effects of electrostatic acceleration and the Compton drag interaction are determined. In the course of their deceleration, the charged particles boost the thermal disk radiation to gamma-ray energies, which may result in a significant spectral component. Cold disks are too underluminous to significantly retard the flow, and if such disks are present in pulsars, only a small fraction of the particle energy is transferred to the radiation field. The results also indicate that steady, unidirectional particle acceleration is unlikely to be the mechanism operating in gamma-ray burst sources.

Melia, Fulvio↗
NASA NTRS1989

Transient X-rays, gamma-rays and neutrons in space

The various astrophysical sources of transient X-ray, gamma-ray, and neutron emission which can produce significant increases in the high-energy (greater than 1 keV) radiation and particle background flux in space. These sources include solar flares, gamma-ray bursts, supernovae, and other astrophysical transients. The observations of these sources are reviewed, and the expected rate of occurrence of their transient emission is examined as a function of intensity and energy.

Lingenfelter, R. E.↗