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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Persistent emission from X-ray burst sources and the nature of galactic bulge X-ray sources

Intrinsic persistent emission from galactic bulge X-ray sources and the ratio of the average persistent X-ray luminosity to the time-averaged burst luminosity associated with Type I burst sources are discussed in the light of the thermonuclear flash model of X-ray burst emission. Values of the ratio between average persistent luminosity and time-averaged burst luminosity for a large collection of SAS 3 sources are presented to confirm the predictions of the burst model of thermonuclear flashes in freshly accreted matter on a neutron star. The model also predicts a critical value of the persistent accretion rate, below which bursts can occur. It is suggested that the galactic bulge X-ray sources represent neutron stars undergoing accretion, with burst sources accounting for a subset in which the accretion rate is below the critical value.

Van Paradijs, J.↗
NASA NTRS1980

Observations of Cygnus X-3 with the Einstein /HEAO 2/ X-ray Observatory The period derivative and the asymmetric X-ray light curve

Cygnus X-3 was observed by the Monitor Proportional Counter on the Einstein (HEAO 2) X-ray Observatory for 2.4 days in 1978 December. The analysis of the data from these observations is used in conjunction with a self-consistent re-examination of previous results from the Uhuru, ANS, COS B, and SAS 3 satellites to investigate earlier reports that the 4.8 hour period of Cygnus X-3 is increasing. It is found that there is indeed a period derivative, P = (1.78 plus or minus 0.40) x 10 to the -9th s/s, which confirms the principal conclusion of previous authors. The possibility that the X-ray source is in an elliptical orbit and that some, or all, of the observed period derivative may be due to apsidal motion is discussed. The elliptic orbit hypothesis explains the observed asymmetry in the average X-ray light curve and leads to the conclusion that the most likely companion to the X-ray source is a helium star, possibly with a light hydrogen envelope

Elsner, R. F.↗
NASA NTRS1981

Gamma ray lines from the Galactic Center and gamma ray transients

The observations and interpretations of cosmic (nonsolar) gamma ray lines are discussed. The most prominent of these lines is the e(+)e(-) annihilation line which was observed from the Galactic Center and from several gamma ray transients. At the Galactic Center the e(+)e(-) pairs are probably produced by an accreting massive black hole (solar mass of approximately one million) and annihilate within the central light year to produce a line at almost exactly 0.511 MeV. In gamma ray transients the annihilation line is redshifted by factors consistent with neutron star surface redshifts. Other observed transient gamma ray lines appear to be due to cyclotron absorption in the strong magnetic fields of neutron stars, and nuclear deexcitations and neutron capture, which could also occur on or around these objects.

Ramaty, R.↗
NASA NTRS1980

Actinide cosmic ray chronometers - Relative abundances and the cosmic ray lifetime

Measurements of ultraheavy cosmic rays will provide radioactive chronometers, including the actinides, which are expected to be present in the source. These primary chronometers differ from the Be-10 secondary chronometer in total inelastic cross-section and decay half-life. A propagation code, which includes nuclear fragmentation, radioactive decay, and ionization energy-loss of cosmic rays is being used to investigate the variations in the fluxes and mean ages which would be expected for various models of cosmic ray propagation. Some preliminary results in the actinide region are presented here which indicate that measurements of the relative abundances of the actinides in the cosmic rays will be very useful for understanding source abundances but less useful for studying propagation effects.

Margolis, S. H.↗
NASA NTRS1981

Images of single X-ray photons from X-ray phosphor screens

Photographs show the efficiency and resolution characteristics of single X-ray photons converted to optical photons in a variety of commercial X-ray phosphor screens. The recording system uses a cooled, two-stage image intensifier system with fiber optics coupling to the phosphor screen. High efficiencies in the energy range 20-100 keV with position resolution of the order 200 microns are readily achievable, although the sensitive area is presently limited. Potential applications include X-ray astronomy, high-speed X-ray diffractometry, and extremely low dose radiography.

Fishman, G. J.↗
NASA NTRS1981

X-ray and optical observations of the November 19, 1978 gamma-ray burst source region

The Nov. 19, 1978 gamma-ray burst (GRB) has a very well determined error box, 10 square arcmin (Cline et al., 1981). An 8000-sec IPC exposure with the Einstein Observatory detected, at a 3.4-sigma level, one low intensity (less than 3 x 10 to the -13th erg/sq cm per sec) X-ray source inside the error box. The probability of a serendipitous detection was 0.01. Inside the X-ray source error box there are two weak radio sources, one of them highly polarized (Hjellming and Ewald, 1981), and two 20-magnitude objects, not coincident with the radio sources visible in the ESO/SRC J and R plates. With the exception of N49, this is the first possible detection of X-ray emission inside a GRB box. Its low intensity justifies, in fact, the lack of detection for other events.

Pizzichini, G.↗
NASA NTRS1982

A magnitude limited stellar X-ray survey and the F star X-ray luminosity function

An X-ray survey has been conducted of stars brighter than visual magnitude 8.5 that have serendipitously fallen into the fields of view of the Imaging Proportional Counter of the Einstein Observatory. The survey includes 227 separate 1 x 1 deg fields, containing 274 stars with a visual magnitude of no more than 8.5 and covering a wide range of spectral types and luminosity classes. X-ray emission was detected from 33 stars, and upper limits have been determined for the remainder of the sample. F type stars dominate the detected sample, and most of these are shown to be dwarfs. An X-ray luminosity function for dF stars has been deduced, and reveals that the average 0.2-4.0 keV luminosity of these stars is around 10 to the 29th erg/sec. Constraints have been placed on the high luminosity tails and medians of the X-ray luminosity functions for other types of stars.

Topka, K.↗
NASA NTRS1983

A search for X-ray polarization in cosmic X-ray sources

Fifteen strong X-ray sources were observed by the X-ray polarimeters on board the OSO-8 satellite from 1975 to 1978. The final results of this search for X-ray polarization in cosmic sources are presented in the form of upper limits for the ten sources which are discussed elsewhere. These limits in all cases are consistent with a thermal origin for the X-ray emission.

Hughes, J. P.↗
NASA NTRS1984

A search for X-ray polarization in cosmic X-ray sources

Fifteen strong X-ray sources were observed by the X-ray polarimeters on board the OSO 8 satellite from 1975 to 1978. The final results of this search for X-ray polarization in cosmic sources are presented in the form of upper limits for the 10 sources which have not been discussed elsewhere. These limits in all cases are consistent with a thermal origin for the X-ray emission.

Hughes, J. P.↗
NASA NTRS1985

Three-dimensional and tomographic imaging device for X-ray and gamma-ray emitting objects

An instrument for obtaining quantitative, three-dimensional and tomographic information relating to X-ray and gamma-ray emitting objects and for the orthoscopic viewing of such objects includes a multiple-pinhole aperture plate held spaced from an X-ray or gamma-ray to visible-light converter which is coupled to a visible-light image intensifier. The spacing between the aperture plate and the converter is chosen such that the mini-images of an emitting object formed by the pinholes do not substantially overlap as they impinge on the converter. The output of the image intensifier is digitized by a digitizing camera in terms of position and intensity and fed into a digital computer. The computer may output quantitative information relating to the emitting object directly, such as that relating to tomograms, or provide information in analogue form when coupled with a suitable viewing device to give an orthoscopic, three-dimensional image of the object.

Yin, L. I.↗
NASA NTRS1985

Balloon observations of hard X-rays from NGC 4151 and an X-ray transient source

An X-ray telescope consisting of 400 sq cm phoswich detectors (NaI(Tl)/CsI(Na)) was flown from Hyderabad (India) on 31 October 1980; the field of view was 11 deg x 1 deg FWHM. During a five hour observation at 5 millibars two X-ray sources were seen: (1) the variable Seyfert Galaxy NGC 4151; and (2) a transident of approximately 8 minutes duration in the vicinity of the variable source 4U1444 43 which may be associated with the galaxy NGC 5608. X-ray fluxes and spectra in 18-120 keV X-rays are presented.

Kunte, P. K.↗
NASA NTRS1985

Radial distribution of cosmic ray intensity in the galaxy from gamma-ray data

The radial distributions of Galactic gamma-ray emissivity and cosmic ray intensity are derived by unfolding the SAS2 line flux data. The results show a marked gradient, with the cosmic ray intensity in the region 3,R,7 kpc being 3 to 4 times as much as locally. There is also an indication for a higher gradient for cosmic rays of lower energy.

Goned, A.↗
NASA NTRS1984

HEAO 1 high-energy X-ray observations of three bright transient X-ray sources H1705-250 (Nova Ophiuchi), H1743-322, and H1833-077 (Scutum X-1)

The bright X-ray transients H1705-250 (Nova Ophiuchi) and H1743-322 in the energy range 12-180 keV were observed, and the presence of high-energy spectral components was revealed. On the basis of X-ray spectra in the 1-10 keV range, transients are classified as 'soft' (kT = 4 keV) or 'hard' (kT = 17 keV); and both H1705-250 and H1743-322 should be in the 'soft' category. Data have been reexamined for the archetypal 'soft' transient A0600-00 taken by the SAS 3 satellite, but no evidence is found there for a high-energy spectral component. Thus consideration of a wider X-ray energy range makes the 'hard'/'soft' distinction between X-ray transients much less clear.

Cooke, B. A.↗
NASA NTRS1983

Detection of cosmic ray electrons above 10 to 14th eV using gamma ray observatories

A quantitative evaluation of high energy gamma ray observatories for the study of cosmic ray electrons is made. This is based on the principle that the synchrotron photons emitted by the electrons in the earth's magnetic field is collinear in the detector. It is shown that the size and the gamma ray detection efficiency of the SAS II instrument is so small, that no useful information can be derived from it. On the other hand, one may be able to set useful upper limits to the flux of electrons by making use of the high energy gamma ray detector in the GRO.

Stephens, S. A.↗
NASA NTRS1986

Preliminary designs for X-ray source modifications for the Marshall Space Flight Center's X-ray calibration facility

The objective of this investigation is to develop preliminary designs for modifications to the X-ray source of the MSFC X-Ray Calibration Facility. Recommendations are made regarding: (1) the production of an unpolarized X-ray beam, (2) modification of the source to provide characteristic X-rays with energies up to 40 keV, and (3) addition of the capability to calibrate instruments in the extreme ultraviolet wavelength region.

Croft, W. L.↗
NASA NTRS1986

Rapid X-ray and optical variability in the X-ray selected BL Lacertae object IE 1402.3 + 0416

Results from X-ray and optical observations of the X-ray-discovered BL Lac object 1E 1402.3 + 0416 are presented, where the X-ray measurements were carried out with the Channel Multiplier Array (CMA) and Medium Energy experiment (ME) detectors on board Exosat. These measurements revealed an intensity decrease by a factor of two on a time scale of a few hours. At maximum flux, the source was significantly greater than at the time of the Einstein Image Proportional Counter (IPC) discovery observation. The 2-6 keV X-ray spectrum was determined by the ME experiment, and IPC, HRI, and CMA data were subsequently compared. The source varied over the years by a factor of five; its brightest state was within the last three years. It is noted that a redshift greater than 0.2 would require that anisotropic emission mechanisms be invoked.

Giommi, P.↗
NASA NTRS1987

EX56a study of extended X-ray emission around isolated galaxies EX56b identification and spectra of bright X-ray sources at high galactic latitude

The EXOSAT observations confirmed the identification and extended nature of PKS 2345-35. It gave a good 2 to 10 keV X-ray spectrum and a detailed spatial profile indicating asymmetry of the structure. In the high galactic latitidue investigation, the BL Lac object identified with the HEAO-1 source 1430+423 was detected, and the first X-ray spectrum was obtained. Several simulataneous observations of H0323+022 were obtained over a broad range of electromagnetic spectrum. Studies of luminous active galactic nuclei have given significant information on the spectrum of the quasar PKS 0558-504. In a study of Southern sky cataclysmic variables, the EXOSAT was used to determine the X-ray spectrum and search for periodicities in two objects. Studies of complete identifications have revealed that X-ray sources in two high galactic latitude fields are stars, and therefore are to be excluded from the Piccinotti extragalactic sample. Only one Piccinotti source remains to be identified.

Schwartz, Daniel A.↗
NASA NTRS1986

Modifications of the X-ray source and monitor at the X-ray Calibration Facility

In order to test the instruments aboard the Advanced X-ray Astrophysics Facility (AXAF) some modifications will need to be made in the X-ray Calibration Facility at Marshall. Several of these modifications involve the X-ray source and the monitor. The source was redesigned to increase the spectral purity of the beam and decrease its polarization by minimizing the number of bremsstrahlung photons in the beam. This was accomplished by utilizing an annular electron gun which allowed the beam to take off antiparallel to the direction at which electrons are incident on the anode. Two other features of the source are the conical anode which decreases the effective spot size and a rotatable anode and filter wheel which allow the operator to change targets without breaking vacuum. The monitor is an important part of the facility because it is used to determine the X-ray flux at the target. A commercially available solid-state detector, Si(Li), should be used along with appropriate proportional counters for monitoring. This detector will be particularly useful when energy or wavelength dispersive instruments are tested because of its good resolution.

Newbolt, W. Barlow↗