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At least 1,621 records · Page 90
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NASA NTRS1981

Evolution of X-ray astronomy

The evolution of X-ray astronomy up to the launching of the Einstein observatory is presented. The evaluation proceeded through the following major steps: (1) discovery of an extrasolar X-ray source, Sco X-1, orders of magnitude stronger than astronomers believed might exist; (2) identification of a strong X-ray source with the Crab Nebula; (3) identification of Sco X-1 with a faint, peculiar optical object; (4) demonstration that X-ray stars are binary systems, each consisting of a collapsed object accreting matter from an ordinary star; (5) discovery of X-ray bursts; (6) discovery of exceedingly strong X-ray emission from active galaxies, quasars and clusters of galaxies; (7) demonstration that the principal X-ray source is a hot gas filling the space between galaxies.

Rossj, B.↗
NASA NTRS1982

The X-ray binary, UW CMa

The UW CMa is a close, eclipsing binary composed of an O7f primary with a stron wind and a less luminous O-type companion. It was found that UW CMa a variable X-ray source, whose X-ray variations are in phase with its optical light curve. Since both components of the binary system are O stars, accretion by a compact object is ruled out as a mechanism for generating X-rays. The UW CMa represents a new class of X-ray binaries, in which X-rays result from the collision of a wind from one star with the surface or wind of the other star. It is hypothesised that the impact of a wind against a star generates a shock wave about 0.25 stellar radii above the stellar surface, and material behind the shock front, heated to bout 10 million degrees, radiates the X-ray apparent X-ray variability is due to its location between the two stars, where it undergoes eclipses. The high temperature region maintains an ionization cavity in the wind, as detected with IUE. The ionization cavity is the source of depletion of absorbing ions in the wind between the two stars.

Heap, S. R.↗
NASA NTRS1981

X-ray scanning of overhead aurorae from rockets

Two Nike Tomahawk rocket payloads were launched into energetic auroral events in September, 1976 to investigate the structure of these events, as well as their effects on the atmosphere. X-ray scintillation detectors with energy discrimination in four ranges were used to measure the deposition of bremsstrahlung produced X-rays within the stratosphere and mesosphere. Iterative computer techniques were used to reconstruct X-ray source maps at 100 km, taking atmospheric absorption effects into account. Payload 18.178 was launched on September 21st into an aurora having two distinct azimuthal regions of optical brightness. The X-ray scanner detected the same features, and overlays of the X-ray source maps on all-sky photographs showed spatial coincidence of the X-ray with optical features at the lower energies (below 40 keV). Payload 18.179 was launched September 23rd into an aurora with a more diffuse character. The optical structure did not coincide as well with the measured X-ray structure. There was also an indication of a two-component spectrum for each event, with the hard component originating in the more diffuse, optically faint regions.

Barcus, J. R.↗
NASA NTRS1980

X-ray bursters

The main properties of X-ray bursts, as well as the value of these bursts for understanding low-mass X-ray binaries, are discussed. The analysis of the X-ray spectrum of bursts during their decay has provided evidence that X-ray bursts arise from neutron stars. It is thus illustrated how observations of the X-ray bursts may be used to obtain information about the properties of neutron stars. In particular, a method for measuring the radii of neutron stars from observations of X-ray bursts is proposed, based on the results of the blackbody radii of X-ray bursters.

Van Paradijs, J.↗
NASA NTRS1982

The elemental and isotopic composition of galactic cosmic rays

Galactic cosmic rays represent samples of matter from areas outside the solar system. New information regarding the elemental composition of cosmic rays has been obtained in connection with the French-Danish experiment on HEA0-3 and recent balloon experiments. The energy dependence of the source composition is considered along with a comparison of cosmic ray and solar system abundances, and the N-14 source abundance. Attention is given to cosmic ray clocks and the Mn-54 problem, advances concerning cross section measurements, and cosmic ray isotopes. The considered new observations suggest that cosmic ray elemental abundance differences from the solar system continue to be ordered by atomic parameters such as first ionization potential, at least up through Z equals 40. The isotopic composition of the cosmic ray source is found to be unlike that of the solar system.

Mewaldt, R. A.↗
NASA NTRS1982

Soft X-rays from the sunlit earth's atmosphere

Observations of soft X-ray emission from the sunlit earth atmosphere are presented and compared with the predictions of an earth albedo X-ray theory. The exact theory accounts for the flux of Thomson scattered solar X rays and fluorescently excited K X rays that arise following the absorption of incident X rays as a function of observing geometry. Observations were made at widely separated geometries with the two low-energy detectors of the A-2 experiment on the HEAO-1 satellite. Fitting of the model to the observed spectra results in values for the solar coronal temperature and emission measure that are in good agreement with expected values for the nonflaring sun, indicating that X-ray observations of the sunlit atmosphere may be a useful monitor of solar activity for satellites unable to view the sun directly. The total measured fluorescent line flux is also in agreement with calculations, although the N/O line ratio is not. X-ray fluorescence measurements from the sunlit atmosphere will thus be useful in monitoring atmospheric composition only to the extent that the total line counting rates depend upon the composition.

Mckenzie, D. L.↗
NASA NTRS1982

Radio and X-ray structure of Centaurus A

Recent studies of the nearby radio galaxy Centaurus A with the Very Large Array and the Einstein X-Ray Observatory reveal complex radio and X-ray structures. A prominent one-sided jet comprised of resolved knots located 0.2-6 kpc from the nucleus is seen in both radio and X-rays. The X-ray emission is probably synchrotron, requiring in situ reacceleration up to about ten million. Inverse Compton emission is not a likely explanation though a thermal model in which the nucleus ejects dense 100,000 solar mass clouds cannot be excluded. An elongated X-ray region is also found near the 'middle' radio lobe and optical HII regions about 30 kpc NE of the nucleus. Conditions around the active nucleus, the absence of X-rays from the inner radio lobes, and X-ray evidence for a hot interstellar medium are briefly discussed

Feigelson, E. D.↗
NASA NTRS1981

Extended range X-ray telescope

An X-ray telescope system is described which is comprised of a tubular mount having a collecting region remote from the one axial end. A soft X-ray/XUV subsystem associated with the collecting region directs only relatively soft, near on-axis X-rays/XUV radiation incident on a first portion of the collecting region into a first detector sensitive to relatively soft X-rays/XUV radiation. A hard X-ray subsystem associated with the collecting region directs only relatively hard near on-axis X-rays incident on a second portion of the collecting region into a second detector sensitive to relatively hard X-rays.

Hoover, R. B.↗
NASA NTRS1983

X-ray, radio, and infrared observations of the 'rapid burster' /MXB 1730-335/ during 1979 and 1980

The paper reports partially simultaneous observations of the 'rapid burster' (MXB 1730-335) at X-ray, infrared, and radio wavelengths, covering several hundred hours during 1979 and 1980. None of the authors of this report saw any infrared or radio bursts. On several occasions an absence of infrared bursting was observed during X-ray bursting. On one occasion an absence of X-ray bursting was observed during a radio burst (4.1 GHz) reported by Calla et al. (1979). To date, radio bursts (a total of at least a dozen) have been reported only by Calla et al. (1980). Considering these and other observations summarized here, the reported radio bursts are either unreal or do not bear a simple relation to the X-ray bursts from the 'rapid burster'. The status of the reported infrared bursts also remain ambiguous. Limits to the brightness of any persistent radio source at the position of MXB 1730-335, limits to persistent X-ray emission during an extended X-ray quiet phase, and a measurement of the infrared polarization in the direction of the X-ray source are also reported.

Lawrence, A.↗
NASA NTRS1983

X-ray studies of quasars with the Einstein Observatory. III The 3CR sample

Using X-ray emission detected by the Einstein Observatory from each of the 33 3CR quasars in Schmidt's complete sample, it is demonstrated that there is a relationship between the X-ray emission and centimeter wavelength radio emission even for steep-spectrum quasars, provided that only the radio emission from the central object is considered. The observations are summarized, and the estimation of the X-ray luminosity distribution, rather narrow compared to the radio and optical luminosity distributions, is presented. The relationship between X-ray and radio emission is discussed, as is the cosmological evolution of the X-ray luminosity function. The relationship between X-ray and optical luminosity provides an explanation for the finding that X-ray selected quasars have lower redshifts than optically selected quasars of the same optical magnitude.

Tananbaum, H.↗
NASA NTRS1983

The correlated X-ray and optical time variability of TT Arietis

The results of Einstein X-ray observation and simultaneous optical observations of the cataclysmic variable TT Arietis extending over several binary orbits are reported. Evidence is found for correlations between the X-ray and optical variability of TT Ari on three distinct time scales: the 3.3 hour variability that has been associated with the orbital period of the star, the about 1000 s time scale of the irregular flickering activity, and the time scale of quasi-coherent oscillations which have periods of order 10 s. There is a modulation of the X-ray flux with a period consistent with the orbital period of approximately 200 minutes, but there is no apparent modulation of the X-ray spectrum. The optical flux is modulated with a similar period and may lag the X-ray modulation by about 0.1 in phase. The X-ray spectrum is well fitted by a thermal bremsstrahlung plus Gaunt factor model. The results suggest that the hard X-ray emission may be produced in a corona above and below the inner accretion disk.

Jensen, K. A.↗
NASA NTRS1983

The discovery of an X-ray bright BL Lacertae object - 0414 + 009

X-ray, optical, and radio observations have been made of an X-ray source originally discovered by Ulmer et al. (1980) in a survey of Abell clusters of galaxies. The relatively flat radio spectrum, the featureless optical spectrum, and the shape of the X-ray spectrum lead to the classification of the source as a BL Lacertae object. The source has one of the highest X-ray flux density ratios to both the optical and radio flux densities, and its strength at all these wavelengths warrants further multiwavelength studies. The radio, optical, and X-ray flux densities for the observations were 100 mJy, V = 16.4 (1 mJy), and 1 UFU (1.6 micro Jy). The X-ray flux varied by a factor of 2 over a 1 year period, but no 100 s time scale variations were seen. A search of the Harvard plate stacks did not reveal any optical variations. A model for the source is presented, and the implications of this object with respect to X-ray surveys are briefly discussed.

Brown, R. L.↗
NASA NTRS1984

Real-time X-ray Diffraction: Applications to Materials Characterization

With the high speed growth of materials it becomes necessary to develop measuring systems which also have the capabilities of characterizing these materials at high speeds. One of the conventional techniques of characterizing materials was X-ray diffraction. Film, which is the oldest method of recording the X-ray diffraction phenomenon, is not quite adequate in most circumstances to record fast changing events. Even though conventional proportional counters and scintillation counters can provide the speed necessary to record these changing events, they lack the ability to provide image information which may be important in some types of experiment or production arrangements. A selected number of novel applications of using X-ray diffraction to characterize materials in real-time are discussed. Also, device characteristics of some X-ray intensifiers useful in instantaneous X-ray diffraction applications briefly presented. Real-time X-ray diffraction experiments with the incorporation of image X-ray intensification add a new dimension in the characterization of materials. The uses of real-time image intensification in laboratory and production arrangements are quite unlimited and their application depends more upon the ingenuity of the scientist or engineer.

Rosemeier, R. G.↗
NASA NTRS1984

X-ray observations of a large sample of cataclysmic variable stars using the Einstein Observatory

This paper presents the results of an X-ray survey of 31 known or suspected cataclysmic variables. Eighteen of these close binary systems are detected with inferred luminosities in the 0.1-4.0 keV band of between 10 to the 30th and 10 to the 32nd erg/sec. The majority have relatively hard X-ray spectra (kT greater than 2 keV) irrespective of luminosity state. Of seven dwarf novae observed during optical outbursts only U Gem exhibited enhanced ultrasoft X-ray emission (kT of about 10 eV) in addition to weak, hard X-ray emission. Variability of the X-ray flux is observed in many of these stars, on time-scales ranging from tens of seconds to hours. The contribution to the flux from extended X-ray emission is investigated for SU UMa and GK Per. Several possibilities for the origin of the hard X-rays are considered.

Cordova, F. A.↗
NASA NTRS1984

An X-ray survey of a complete sample of 3CR radio galaxies

The X-ray survey of the galaxies, 40 in all, was made with the Einstein Observatory. By comparing the distributions of X-ray luminosities, it is found that 3CR galaxies with double radio morphology (FR 2) and optical emission-line spectra tend to be the more powerful X-ray emitters, with broad-line galaxies at the top of the distribution. It is also found that the X-ray luminosity is strongly correlated with the 5 GHz radio nuclear luminosity. Through an analysis of the complete optical and radio sample with the Spearman partial rank correlation technique, it is determined that nuclear radio luminosity at 5 GHz is correlated with both total radio luminosity at 178 MHz and with galaxy optical luminosity. Other weaker correlations are found of the X-ray luminosity with the total radio luminosity at 178 MHz and the optical luminosity of the galaxy. The results are seen as underlining the importance of nuclear phenomena in radio galaxies and indicating a nuclear origin of their X-ray emission. In addition, it is found that the 3CR emission-line galaxies are similar to both Seyfert galaxies and quasars with double radio morphology in their X-ray properties, strongly reinforcing a unified picture of active nuclei.

Fabbiano, G.↗
NASA NTRS1984

Winds in collision. II - An analysis of the X-ray emission from the eruptive symbiotic HM Sge

X-ray emissions from HM Sge obtained in 1981 from the HEAO-2 satellite are analyzed and compared quantitatively with observations of HM Sge made in 1980 and of HM Sge, V 1016 Cyg, and RR Tel made in 1979. The change in the X-ray emission from HM Sge between 1979 and 1981 is found to be consistent with the X-ray luminosity and/or temperature of the emitting region declining with an e-folding timescale of the order of one to several decades. Comparison with X-ray data from V 1016 Cyg and RR Tel gives a composite X-ray light curve that is also consistent with such a decline. A comparison of the X-ray observation with spectroscopic information makes it possible to constrain the properties of the X-ray emitting region: the result is consistent with emission from an optically thin region between the two stars in the system where their winds collide head on. It is also shown that the observations are inconsistent with a stellar (blackbody) source, with emission from an accretion disk around a white dwarf or a neutron star, and with emission from a single star wind from either a white dwarf or a neutron star.

Willson, L. A.↗
NASA NTRS1984

Comparison of solar flare X-ray producing and escaping electrons from about 2 to 100 keV

Using observations from the ISEE-3 spacecraft, the X-ray producing electrons and escaping electons from a solar flare on November 8, 1978 are compared. The instantaneous 5 to 75 keV electron spectrum in the X-ray producing region is computed from the observed bremsstrahlung X-ray spectrum. Assuming that energy loss by Coulomb collisions (thick target) is the dominant electron loss process, the accelerated electron spectrum is obtained. The energy spectrum of the escaping electrons observed from 2 to 100 keV differs significantly from the spectra of the X-ray producing electrons and of the accelerated electrons, even when the energy loss which the escaping electrons experienced during their travel from the sun to the earth is taken into account. The observations are consistent with a model where the escaping electons come from an extended X-ray producing region, which ranges from the chromosphere to high in the corona. In this model, the low energy escaping electrons (2-10 keV) come from the higher part of the extended X-ray source where the overlying column density is low, while the high energy electrons (20-100 keV) come from the entire X-ray source.

Pan, L.-D.↗
NASA NTRS1980

X-ray observations of the Seyfert 1 galaxies AKN120 and MCG8-11-11

A new X-ray source, H0523-00, with the optically variable Seyfert 1 galaxy AKN 120 is identified. The source has a 2-10 keV X-ray flux of 2 x 10 to the -11th ergs/sq cm s which corresponds to a 2-10 keV X-ray luminosity of 10 to the 44th ergs/s. X-ray observations over a 1.5 year time span combined with contemporaneous optical photometry show a decrease in the optical with no corresponding decrease in the X-ray. In contrast, similar observations of MCG 8-11-11 show a contemporaneous decrease in optical and X-ray fluxes. It is noted that the infrared and X-ray spectral slopes for these two objects are similar, with the optical being steeper by roughly one unit.

Mushotzky, R.↗