Search NASA⌕ Search

SEARCH · Search NASA

Results for “X-Ray Astrophysics”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

An imaging gas scintillation proportional counter for use in X-ray astronomy

An imaging gas scintillation proportional counter (GSPC) has been constructed for use in X-ray astronomy. The IGSPC consists of a gas scintillation proportional counter (GSPC) with a 1 micron polypropylene window coupled to a multiwire proportional counter (MWPC) via a calcium fluoride window. The MWPC, filled with a mixture of argon, methane, and tetrakis (dimethylamino) ethylene, detects the UV photons emitted by the xenon gas in the GSPC. The measured energy resolution is 17.0 percent (fwhm) and 8.0 percent (fwhm) at 1.5 keV and 5.9 keV, respectively. The measured position resolution is 1.9 mm (fwhm) and 0.9 mm (fwhm) at 1.5 and 5.9 keV, respectively. Possible astrophysical observations which can be performed with an IGSPC at the focal plane of a grazing incidence telescope are also discussed.

Hailey, C. J.↗
NASA NTRS1983

NASA astrophysics - Optical systems to explore the universe

Major and minor NASA astrophysical research efforts in the near-term are outlined, together with projections of direction for future projects. The Space Telescope is being readied for a 1986 launch and will feature an f/24, 2.4 m aperture, an MgF2 mirror with better than 1/60 wavelength accuracy and will be diffraction-limited in the UV. Pointing accuracy is designed to be 0.007 arcsec for 24 hr. Optical, spectrometric, and photometric equipment will be included. Around 1990, Shuttle-based missions will include an IR telescope and a subarcsec solar surface imaging device. A free-flying X-ray observatory (AXAF) is planned and will include a sensitivity that exceeds that of the HEAO-2 spacecraft by two orders of magnitude. Instruments are under development for higher resolution UV, gamma-ray, and IR studies. In-orbit interferometry is being studied and will depend on in-orbit assembly and servicing of stable structures with segmented optics.

Pellerin, C. J., Jr.↗
NASA NTRS1988

Supernovae and supernova remnants

The basic features and astrophysics of supernovae of types Ia, Ib, and II and of SNRs are discussed, summarizing the results of recent ground-based and space observations obtained at different wavelengths. Typical data are presented in graphs and sample images, and consideration is given to their implications for shock heating by the initial explosion, radioactive energy input, circumstellar interaction, and pulsar energy input. SNRs described include Tycho's remnant, Kepler's remnant, the Cyg loop, Pup A, the Crab Nebula, the Vela and Crab pulsars, and 0540-69.3 in the LMC. The need for high-spatial-resolution IR and X-ray spectra of these objects is indicated.

Chevalier, Roger A.↗
NASA NTRS1985

Interstellar clouds - From a dynamical perspective on their chemistry

The possibility is examined that in the course of its dynamical evolution, a single mass of interstellar gas would exhibit properties of diffuse clouds, dense clouds and finally also of clouds perturbed by shocks or intense UV or X-ray radiation generated by a star of its own creation. This concept provides a common thread through the bewildering diversity of physical and chemical compositional properties shown by interstellar clouds. From this perspective, instead of being static objects, interstellar clouds are possibly incessantly evolving from initially diffuse to later dense state and then to star formation which ultimately restructures or disperses the remaining cloud material to begin the whole evolutionary process once again. Based on a simplified study of interstellar chemistry from a dynamical perspective, the ideas are presented as an heuristic: to encourage thought on the future direction of molecular astrophysics and the need to consider the chemical behavior of interstellar clouds in conjunction with, rather than in isolation from, their dynamical behavior. A physical basis must be sought for the semiempirical temperature formula which has been given a critical role in the collapse of diffuse clouds. Self-shielding effects in the chemistry of CO were neglected and this drawback should be removed; the ability of the model to explain the fractional abundances of more complex molecules, such as cyanopolyynes, should be examined.

Prasad, S. S.↗
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 NTRS1973

High energy and solar astronomy, overview

A survey of our own galaxy and neighboring galaxies using X-rays, gamma rays, and cosmic rays is outlined. High energy astrophysic results suggest the presence of a new acceleration mechanism where the inflow of matter on collapsed objects seems to be one of the sources of complex time variations in binary systems.

Mcdonald, F. B.↗
NASA NTRS1973

Transition radiation in astrophysics.

Transition radiation produced by relativistic electrons traversing cosmic grains is investigated as a possible source of celestial X rays. The detailed theory of transition radiation including the formation-zone effect is used to calculate the X-ray emissivity in interstellar space. It is found that the largest contribution of transition radiation to the observed X-ray emission from the galactic disk is at about 2 keV, where less than about 0.3% of the observed emissivity is due to transition radiation. At higher energies transition radiation is strongly suppressed by the formation-zone effect, while at lower energies the observed emissivity increases much faster with decreasing energy than does transition radiation. Transition radiation is also compared with bremsstrahlung, synchrotron emission, and Compton scattering. The comparison with synchrotron emission and bremsstrahlung relates X-ray production by transition radiation to radio emission and to approximately 100-MeV gamma-ray production, respectively.

Yodh, G. B.↗
NASA NTRS1974

Search for brief celestial X-ray bursts

The occurrence of intense bursts of 0.1- to 1.5-MeV photons from space has been confirmed with observations from IMP-6. This is the first positive result of an extensive data comparison, in which a search was made of OGO and IMP records for time coincidences between brief X- or gamma-ray increases and a variety of other transient phenomena. The IMP-6 measurements provided the first differential energy spectra of these events, the shapes of which indicate that photons predominantly in the gamma-ray domain are released into space. Whether these bursts originate in distant supernovae or in some new class of relatively nearby gamma-ray flare stars, they reveal a process which is new to high-energy astrophysics, not only because of the unusual spectrum, but also because of the brief time scales involved and because of the intense fluxes observed.

Cline, T. L.↗
NASA NTRS1974

High energy particles and quanta in astrophysics

The various subdisciplines of high-energy astrophysics are surveyed in a series of articles which attempt to give an overall view of the subject as a whole by emphasizing the basic physics common to all fields in which high-energy particles and quanta play a role. Successive chapters cover cosmic ray experimental observations, the abundances of nuclei in the cosmic radiation, cosmic electrons, solar modulation, solar particles (observation, relationship to the sun acceleration, interplanetary medium), radio astronomy, galactic X-ray sources, the cosmic X-ray background, and gamma ray astronomy. Individual items are announced in this issue.

Mcdonald, F. B.↗
NASA NTRS1978

Gamma ray spectroscopy in astrophysics

Experimental and theoretical aspects of gamma ray spectroscopy in high energy astrophysics are discussed. Line spectra from solar, stellar, planetary, and cosmic gamma rays are examined as well as HEAO investigations, the prospects of a gamma ray observatory, and follow-on X-ray experiments in space.

Cline, T. L.↗
NASA NTRS1978

Future directions in experimental gamma ray astronomy

Better vehicles and instruments are needed if gamma ray spectroscopy in astrophysics and cosmology is to advance. A gamma ray observatory will (1) permit long-term observations of selected sources to measure their variability and to achieve high sensitivity; (2) measure periods in days or weeks; and (3) assess the entire sky to observe various predicted sources, to measure the energy spectrum, and to map the isotropy of the cosmic ray background over larger collecting areas (of the order of a square meter). Conventional and unconventional instruments must cover the energy range from 0.1 MeV to 20 MeV with improved sensitivity. Angular resolution must be improved one degree or more to study discrete X-ray sources in the galactic center. Actively collimated detectors, improved double Compton instruments, and gamma ray correlators to actively synthesize the absolute energy spectrum of the sky protons are discussed as well as the need for scientific balloons.

Haymes, R. C.↗
NASA NTRS1978

The significance of gamma ray observations for neutrino astronomy

Celestial gamma-rays and neutrinos are formed in some of the same astrophysical interactions, but have important different properties. Measurements of these radiations were used to study the presence and dynamic effects of energetic charged cosmic ray particles, element synthesis and particle acceleration. In addition, since gamma-rays in the energy range from several MeV to at least 10 to the 12th power eV and neutrinos both have very low interaction cross sections, they have a very high penetrating power and reach the earth from almost any part of the galaxy or universe. Therefore, they retain the detailed imprint of spectral, directional and temporal features imposed at their birth, even if they were born in regions opaque to visible light and X-rays.

Fichtel, C. E.↗
NASA NTRS1978

HEAO-A - The first high energy astronomy observatory

The early major findings of the four HEAO-A cosmic X-ray and gamma-ray experiments will be discussed. A comparative analysis of the actual and expected instrument performance will be presented. The unique contributions of high energy astrophysics to the study of the universe will be highlighted with specific HEAO-A observations. Plans for the ongoing observations will be shown. The observatory capabilities will be briefly compared with those of previous satellites.

Speer, F. A.↗
NASA NTRS1982

Future directions in X-ray/gamma-ray observations

Facilities available for X ray and gamma ray astronomical observations in the late 1980s are described, with an emphasis on NASA programs. Current European programs for launching Rosat and Exosat will provide coverage in the 0.4-60 keV energy range. The proposed NASA advanced X ray astrophysics facility is intended to cover the 0.1-8 keV range with higher than 0.5 arcsec resolution. The Japanese Astro-B, scheduled for launch in 1983, observes in the 1-60 keV range. X ray and gamma ray observations are also scheduled for Spacelab flights. The French-Soviet Gamma-1 spark chamber high energy gamma ray telescope is intended for LEO orbit and observations in the energy range above 50 MeV with a 2 deg, 1-5 arcmin resolution. The NASA gamma ray observatory is set for 1988 launch and will feature four instruments to monitor the 60 keV-300 GeV range. Balloon-borne instrumentation will also be launched, with attention given to the medium gamma ray energy range from 1-30 MeV.

Kniffen, D. A.↗
NASA NTRS1984

Soft X-ray opacity in hot and photoionized gases

New calculations are presented of the soft X-ray opacity of gas having cosmic elemental abundances, but in a variety of ionization states. Coronal ionization equilibrium is considered over the range of temperatures 10 to the 4th to 3 x 10 to the 8th K and photoionization equilibrium with power-law and thermal bremsstrahlung spectra over a wide range of ionization parameters. The results are displayed in illustrative figures. For temperatures and ionization parameters commonly found in astrophysical plasmas, the opacity (particularly to photons of equal to or less than 1 keV) can be diminished by substantial factors relative to the state in which all atoms are neutral. As the dominant ionization stages change, the positions and contrasts of prominent K-edges also change.

Krolik, J. H.↗
NASA NTRS1983

A high energy resolution experiment in the hard X-ray range

The Low Energy Gamma-Ray Spectrometer (LEGS), a joint project among NASA/GSFC, CEN-SACLAY, and Rice University, is designed to perform fine energy resolution measurements of astrophysical sources. In its low energy configuration (20-800 keV energy range) the instrument uses three planar detectors (effective area of 53 sq cm) surrounded by a combination of passive Fe and active NaI for shielding and collimation (FOW of about 5 x 10 deg FWHM). In a typical one-day balloon flight, LEGS sensitivity limit (3 sigma) for narrow line features is not greater than about 0.0003 ph/sq cm s (at 100 kev).

Paciesas, W.↗
NASA NTRS1985

Recombination-cascade X-ray spectra of highly charged helium-like ions

It is shown that the relative intensity distribution among the X-ray spectral lines of helium-like ions from the n = 2 states produced through recombination processes such as radiative and charge transfer recombination may be given by considering in detail the radiative cascades following recombination. Model calculations are presented with predicted line ratios for Ar XVII and Fe XXV in recombination-dominated noncoronal plasmas. In particular, compared to coronal intensities, the singlet resonance line (w) should be much weaker relative to the triplet intercombination (x, y) and forbidden (z) lines, yielding large values for the ratio G = (x + y + z)/w. Accurate configuration interaction type wave functions are employed to calculate the eigenenergies, transition probabilities, and cascade coefficients. Certain relevant tokamak and astrophysical observations are discussed.

Pradhan, A. K.↗