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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.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Where have all the sources gone?

In the continuing quest for an understanding of the cosmic x-ray background, the most difficult technical barrier remains the mismatch between the wavelength band in which the discrete source populations are best characterized (0.1 to 3.5 keV), and the band in which the spectrum of the background is well determined and the bulk of the energy density resides (3.5 to 50 keV). A progress report in an attempt to resolve this conundrum using the Einstein Imaging Proportional Counter (IPC) database and analysis system is presented. The IPC data base is described and how it can be used to search both for missing clusters of galaxies and highly obscured active galactic nuclei is addressed. All 4083 imaging proportional counter observations were examined after flat fielding and editing to optimize sensitivity for diffuse emission on various size scales ranging up to 10 feet. A '2 sigma source' catalog which, when filtered by matching with source catalogs from other wavelength regimes, is shown to reveal new source classes which may be significant contributors to the cosmic x-ray background is being constructed. Optimization techniques are described and the source catalogs which result are presented. Limits on the contributions both classes of sources make to resolving the discrepancy with the higher energy observations are set.

Helfand, D. J.↗
NASA NTRS1973

Goddard cosmic X-ray experiment for OSO-1

The primary objective of this experiment is to utilize proportional counters of multi-anode multi-layer construction to obtain the spectra of X-ray sources and the diffuse background over the 2 to 60 keV band. Possible broad emission lines, absorption, and spectral breaks in both discrete sources and the diffuse background will be investigated. A schematic representation of this experiment as configured for the OSO-1 wheel and characteristic parameters are summarized.

Boldt, E. A.↗
NASA NTRS1980

Point source contributions to the extreme ultraviolet background

The results of the Apollo-Soyuz extreme ultraviolet (EUV)/soft X-ray diffuse background survey are analyzed to assess the contribution of discrete-sources with blackbody or coronal plasma spectra. Blackbody emitters in the EUV must be less luminous and more numerous than hot white dwarfs in order to produce the bulk of the diffuse flux. Significant contributions to the EUV background appear likely only if sufficient numbers of white dwarfs possess low temperature coronae similar to the one suggested for Sirius B.

Stern, R.↗
NASA NTRS1985

A model for the proton spectrum and cosmic ray anisotropy

The problem of the origin of the cosmic rays is still uncertain. As a theory, it should explain the support of particles and energy, the mechanism of acceleration and propagation as well as some important features obtained directly from cosmic ray experiments, such as the power spectrum and the knee. There are two kinds of models for interpreting the knee of the cosmic ray spectrum. One is the leaky box model. Another model suggests that the cut-off rigidity of the main sources causes the knee. The present paper studies the spectrum and the anisotropy of cosmic rays in an isotropic diffuse model with explosive discrete sources in an infinite galaxy.

Xu, C.↗
NASA NTRS1981

The number-intensity distribution for extragalactic X-ray sources

It is shown that a self-consistent assessment of source count data can be made, if many of the deep survey sources are QSOs which are known to be evolving strongly at fluxes comparable to the survey limits. The QSO contribution would in this case become significant at X-ray fluxes below 10 to the -12th erg/sq cm per sec, and dominates at fluxes below 10 to the -13th erg/sq cm per sec. The X-ray background intensity places a limit on total source counts and requires a turnover in the evolution of X-ray emitting sources. Sources detected in the Einstein survey account for over 35% of the 1-3 keV background flux, suggesting that most of the background is due to discrete sources.

Murray, S. S.↗
NASA NTRS1981

HEAO 1 measurements of the galactic ridge

The HEAO A2 experiment data was systematically searched for unresolved galactic disc emission. Although there were suggestions of non-uniformities in the emission, the data were consistent with a disc of half-thickness 241 + 22 pc and surface emissivity (2-10 keV) at galactic radius R(kpc) of 2.2 10 to the minus 7th power exp(-R/3.5) erg/sq cm to the (-2)power/s (R 7.8 kpc). giving a luminosity of approximately 4.4 10 to the 37th power erg S to the (-1) power. If the model is extrapolated to radii less than 7.8 kpc, the unresolved disc emission is approximately 1.4 10 to the 38th power erg S to the (-1) power (2-10 keV) i.e., a few percent of the luminosity of the galaxy in resolved sources. the disc emission has a spectrum which is significantly softer than that of the high galactic latitude diffuse X-ray background and it is most probably of discrete source origin.

Worrall, D. M.↗
DOE OSTI2022

The channel-source hypothesis: Empirical evidence for in-channel sourcing of dissolved organic carbon to explain hysteresis in a headwater mountain stream

Catchment hydrologists have long puzzled over the question: How can catchments rapidly generate storm flows and pulses of solutes in response to storm events? Conceptual models viewing catchments as composed of discrete source areas generating flow at unique time scales and with unique chemical characteristics have been used to explain the observed changes in flow and water chemistry. Surprisingly, those conceptual models usually do not treat the stream channel as one of the potential source areas. We propose the channel-source hypothesis in which the stream itself should be considered as a potential source with the same rigour as other contributing areas. We pose this in the spirit of the scientific use of the word: a hypothesis is not a proven idea but rather a provisional supposition serving as the basis for further study. We suggest that the channel should be considered as a potential source for dissolved organic carbon (DOC). Channels store substantial amounts of organic matter, and stream ecologists have long studied stream carbon cycling. From those studies, we know that leaching and decomposition can generate DOC from particulate organic carbon (POC). Further, POC is stored in channel ‘dead-zones’—regions of low flow velocity - that can be activated as flow velocity increases, thus releasing accumulated DOC during storms. All catchments are different; there is no reason to assume that channel sources are always important, in every catchment, in every storm. Thus, the channel-source hypothesis does not replace existing conceptual models. Instead, it adds another potential mechanism that may explain DOC dynamics observed in streams. The channel-source hypothesis has substantial implications for catchment studies examining sources of DOC in stream water or using DOC as a tracer to determine the locations of, and proportional contributions of, different source areas for streamflow generation.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1977

Far-infrared scans of the Galactic plane

Results are reported for balloon-borne scans of the Galactic plane between longitudes of 348 and 32.5 deg, which were made in two broad spectral bands from 60 to 300 microns and from 150 to 300 microns. These results indicate that there are many bright H II regions embedded in a diffuse underlying band of emission in the examined longitude range, that the color temperatures range from 30 to 90 K, and that the width of the plane is at least 2 deg of arc in both spectral bands. A lower-limit IR luminosity of the order of 1 billion suns is computed for both the bright complex of sources at the nucleus and the underlying diffuse emission out to about + or -15 deg of arc from the nucleus. The strong relationship between far-IR emission and radio continuum expected for discrete sources is illustrated, and the results are compared with those of previous studies. It is concluded that the total far-IR luminosity of the central part of the Galaxy is understandable solely in terms of known distributions of stars and dust.

Low, F. J.↗
NASA NTRS1978

Some problems with the interpretation of recent microwave background observations in the direction of galaxy clusters, or, beware of negative antenna temperatures

Recently reported observations of the 3-K microwave background in the direction of rich clusters of galaxies should be viewed as placing stringent limits on the mass of cooler ionized gas within the clusters, rather than as a verification of thermal bremsstrahlung models for cluster X-ray sources. At the high radio frequencies employed in the observations, there is a positive contribution to the observed source-brightness distributions from free-free emission by any cooler gas. This can overwhelm the anticipated inverse Compton diminution of the background radiation, even when the total mass in cooler gas is significantly less than the mass of hot plasma required to explain the X-ray source. Future experiments of this type should be conducted only when atmospheric stability is sufficient to permit lengthy drift scans across the clusters. Extreme care must be taken to remove the contributions from any discrete sources.

Tarter, j. C.↗
NASA NTRS1987

The cosmic X-ray background

As the sky in the microwave band is dominated by a cosmic background, so too is the X-ray sky. In this presentation the observational situation regarding the extragalactic X-ray background is reviewed, emphasizing data obtained from HEAO-1 and the Einstein Observatory (HEAO-2). Spectral characteristics and spatial variations are described and discussed within the context of what is currently known about individual extragalactic sources. It is concluded that the bulk of the cosmic X-ray background is yet to be understood. Possibilities range from genuinely diffuse emission to an 'as yet' unknown large population of unresolved discrete sources. The role of cosmological effects is examined and could be important.

Boldt, Elihu↗
NASA NTRS2003

Chandra X-Ray Observatory Observations of the Globular Cluster M28 and its Millisecond Pulsar PSR B1821-24

We report here the results of the first Chandra X-Ray Observatory observations of the globular cluster M28 (NGC 6626). We detect 46 X-ray sources of which 12 lie within one core radius of the center. We show that the apparently extended X-ray core emission seen with the ROSAT HRI is due to the superposition of multiple discrete sources for which we determine the X-ray luminosity function down to a limit of about 6 x 10(exp 30) erg/s. We measure the radial distribution of the X-ray sources and fit it to a King profile finding a core radius of r(sub c,x) approx. 11 sec. We obtain the best-fit mass of the X-ray sources to be M(sub x) approx. 1.9 solar masses. We measure for the first time the unconfused phase-averaged X-ray spectrum of the 3.05-ms pulsar B1821-24 and find it best described by a power law with photon-index Gamma approx. equal to 1.2. We find marginal evidence of an emission line centered at 3.3 kev in the pulsar spectrum, which could be interpreted as cyclotron emission from a corona above the pulsar's polar cap if the the magnetic field is strongly different from a centered dipole. The unabsorbed pulsar flux in the 0.5-8.0 keV band is approx. 3.5 x 10(exp -13) ergs/s/sq cm. We present spectral analyses of the 5 brightest unidentified sources. Based on the spectral parameters of the brightest of these sources, we suggest that it is a transiently accreting neutron star in a low-mass X-ray binary, in quiescence. Fitting its spectrum with a hydrogen neutron star atmosphere model yields the effective temperature T(sup infinity)(sub eff) = 90(sup +30)(sub -10) eV and the radius R(sup infinity)(sub NS) = 14.5(sup +6.9)(sub -3.8) km. In addition to the resolved sources, we detect fainter, unresolved X-ray emission from the central core. Using the Chandra-derived positions, we also present a preliminary report on the result of searching archival Hubble Space Telescope data for possible optical counterparts.

Becker, Werner↗
NASA NTRS2003

Chandra Observations of M28

We report the results of the first Chandra X-Ray Observatory observations of the globular cluster M28 (NGC 6626). We detect 46 X-ray sources of which 12 lie within one core radius of the center. We show that the apparently extended X-ray core emission seen with the ROSAT HRI is due to the superposition of multiple discrete sources for which we determine the X-ray luminosity function down to a limit of about $6\times 10(exp 30)$ erg/s$. We measure for the first time the unconfused phase-averaged X-ray spectrum of the 3.05-ms pulsar B 1821-24. We also present spectral analyses of the 5 brightest unidentified sources.

Weisskopf, Martin↗
NASA NTRS2003

Chandra X-Ray Observatory Observations of the Globular Cluster M28 and its Milisecond Pulsar PSR B1821-24

We report here the results of the first Chandra X-Ray Observatory observations of the globular cluster M28 (NGC 6626). We detect 46 X-ray sources, of which 12 lie within 1 core radius of the center. We show that the apparently extended X-ray core emission seen with the ROSAT HRI is due to the superposition of multiple discrete sources, for which we determine the X-ray luminosity function down to a limit of about 6 x 10(exp 30) ergs/s. We measure the radial distribution of the X-ray sources and fit it to a King profile finding a core radius of r(sub c,X) approx. = 5 11". We measure for the first time the unconfused phase-averaged X-ray spectrum of the 3.05 ms pulsar B1821-24 and find that it is best described by a power law with photon index Gamma approx. = 1.2. We find marginal evidence of an emission line centered at 3.3 keV in the pulsar spectrum, which could be interpreted as cyclotron emission from a corona above the pulsar s polar cap if the magnetic field is strongly different from a centered dipole. The unabsorbed pulsar flux in the 0.1 - 8.0 keV band is approx. = 3.5 x 10(exp -13) ergs/s sq cm. We present spectral analyses of the five brightest unidentified sources. Based on the spectral parameters of the brightest of these sources, we suggest that it is a transiently accreting neutron star in a low-mass X-ray binary, in quiescence. Fitting its spectrum with a hydrogen neutron star atmosphere model yields the effective temperature T(sub eff, sup infinity) = 90(sup +30, sub -10) eV and the radius R(sub NS, sup infinity) = 14.5(sup +6.9, sub -3.8) km. In addition to the resolved sources, we detect fainter, unresolved X-ray emission from the central core. Using the Chandra-derived positions, we also report on the result of searching archival Hubble Space Telescope data for possible optical counterparts.

Becker, Werner↗
NASA NTRS1984

Images in the rocket ultraviolet - Photometry of M101

It is pointed out that ultraviolet imagery of spiral galaxies is a sensitive probe of the large-scale morphology of the star-forming regions and the associated interstellar dust. A rocket-borne Ritchey-Chretien telescope was employed to obtain three ultraviolet images of the Sc 1 galaxy M101 (NGC 5457). The present investigation is concerned with the procedures for reduction and absolute calibration of the obtained images and an analysis in terms of discrete sources. Attention is also given to the radial variation and the azimuthal variation of disk and arms. It is found that the emission from M101 in the UV bandpass is dominated by extreme Population I, in the form of discrete OB/H II complexes.

Hill, J. K.↗
NASA NTRS1979

The galactic gamma-ray flux in the 0.06-5 MeV range

The observed variation of the 72-200-keV count rate in the Apollo gamma-ray spectrometer on Apollo 16 are interpreted as being due to cosmic gamma rays associated with the Crab Nebula, Cyg X-1, and the galactic-center source. A low-resolution map is presented which shows a great enhancement in the galactic-center region; a spectrum for this region is obtained. The shape of the spectrum suggests that the emission originates from an ensemble of discrete sources. It is concluded that the gamma-ray line at 4.4 MeV is not emitted as a constant fraction of the continuum in the whole region of the galactic plane between longitudes of -50 and +22 deg.

Gilman, D.↗
NASA NTRS1991

Origins of the 12-200 micron flux in NGC 6946 - Starlight and continuum dust emission from AN Sc galaxy

Infrared maps and optical CCD images of NGC 6946, a nearly face-on spiral with evidence of active star formation, are presented. Consideration is given, at 1-3 kpc spatial scales, to the relationship of the infrared continuum to spiral and radial structure, tracers of the interstellar medium, and ionizing and nonionizing sources of stellar radiation. Two infrared components were revealed - one with surface brightnesses of 20-60 Jy per 45 arcsec aperture at 160 microns, and the other with a surface brightness of less than 20 Jy. Various continuum distributions show discrete sources coinciding with giant H II regions superposed on a smooth unresolved disk background which decreases exponentially with the radius. The optical and spectral properties of the nuclear source and the disk are described. Dust properties and heating conditions, and far-infrared emitting phases are discussed.

Engargiola, G.↗
NASA NTRS1984

Submillimeter wavelength survey of the galactic plane from l = -5 deg to l = +62 deg: Structure and energetics of the inner disk

Results from a large scale survey of the first quadrant of the Milky Way galactic plane at wavelengths of 150, 250, and 300 microns with a 10x10 arcmin beam are presented. The emission detected in the survey arises from compact sources, most of which are identified with known peaks of 5 GHz and/or CO emission, and from an underlying diffuse background with a typical angular width of approximately 0.9 deg (FWHM) which accounts for most of the emission. A total of 80 prominent discrete sources were identified and characterized, of which about half were not previously reported at far infrared wavelengths. The total infrared luminosity within the solar circle is approximately 1 to 2x10 to the 10th power L sub 0, and is probably emitted by dust that resides in molecular clouds.

Hauser, M. G.↗
NASA NTRS1984

Submillimeter wavelength survey of the galactic plane from l = -5 deg to l = +62 deg - Structure and energetics of the inner disk

Observational results are presented from a new large-scale survey of the first quadrant of the galactic plane at wavelengths of 150, 250, and 300 microns, with a 10 x 10 arcmin beam. The emission detected in the survey arises from compact sources, most of which are identified with known peaks of 5 GHz or CO emission, or both, and from an underlying diffuse background with a typical angular width of about 0.9 deg (FWHM) which accounts for most of the emission. A total of 80 prominent discrete sources are identified and characterized, of which about half have not previously been reported at far-infrared wavelengths. The total infrared luminosity within the solar circle is about 1 to 2 x 10 to the 10th solar luminosity, and is probably emitted by dust that resides in molecular clouds.

Hauser, M. G.↗