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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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NASA NTRS1984

The unusually soft X-ray spectrum of LMC X-3

Spectral studies of LMC X-3 using the HEAO 1 A-2 experiment and the Einstein Solid State Spectrometer show that the X-ray spectrum is extremely soft relative to the vast majority of galactic accretion-driven X-ray sources, but similar to that of black hole candidates in their 'high state'. Rapid approximately 1 s flickering comparable to that seen from Cyg X-1 in its low state was not detected. In the 1977-1979 interval LMC X-3 was for most (if not all) of its time in a 'high state'. The fact that several other steady and transient X-ray sources also have similarly soft X-ray spectra and should be regarded as potential black hole candidates is noted. The spectra of these sources are not well described by any one simple model.

White, N. E.↗
NASA NTRS1975

Spectroscopic analysis of solar and cosmic X-ray spectra. 1: The nature of cosmic X-ray spectra and proposed analytical techniques

Techniques for the study of the solar corona are reviewed as an introduction to a discussion of modifications required for the study of cosmic sources. Spectroscopic analysis of individual sources and the interstellar medium is considered. The latter was studied via analysis of its effect on the spectra of selected individual sources. The effects of various characteristics of the ISM, including the presence of grains, molecules, and ionization, are first discussed, and the development of ISM models is described. The expected spectral structure of individual cosmic sources is then reviewed with emphasis on supernovae remnants and binary X-ray sources. The observational and analytical requirements imposed by the characteristics of these sources are identified, and prospects for the analysis of abundances and the study of physical parameters within them are assessed. Prospects for the spectroscopic study of other classes of X-ray sources are also discussed.

Walker, A. B. C., Jr.↗
NASA NTRS2005

X-RAY OBSERVATIONS OF THE BLACK HOLE TRANSIENT 4U 1630-47 DURING 2 YEARS OF X-RAY ACTIVITY

The black hole candidate (BHC) X-ray transient 4U 1630-47 continuously produced strong X-ray emission for more than 2 years during its 2002-2004 outburst, which is one of the brightest and longest outbursts ever seen from this source. We use more than 300 observations made with the Rossi X-Ray Timing Explorer (RXTE) to study the source throughout the outburst, along with hard X-ray images from the International Gamma-Ray Astrophysics Laboratory (INTEGRAL), which are critical for interpreting the RXTE data in this crowded field. The source exhibits extreme behaviors, which can be interpreted as an indication that the system luminosity approaches the Eddington limit. For 15 observations, fitting the spectral continuum with a disk-blackbody plus power-law model results in measured inner disk temperatures between 2.7 and 3.8 keV, and such temperatures are only rivaled by the brightest BHC systems, such as GRS 1915+105 and XTE J1550-564. If the high temperatures are caused by the dominance of electron scattering opacity in the inner regions of the accretion disk, it is theoretically required that the source luminosity be considerably higher than 20% of the Eddington limit. We detect a variety of high-amplitude variability, including hard 10-100 s flares, which peak at levels as much as 2-3 times higher than nonflare levels. The X-ray properties in 2002-2004 are significantly different from those seen during the 1998 outburst, which is the only outburst with detected radio jet emission. Our results support the "jet line" concept recently advanced by Fender and coworkers. Our study allows for a test of the quantitative McClintock & Remillard spectral state definitions, and we find that these definitions alone do not provide a complete description of the outburst. Finally, for several of the observations, the high-energy emission is dominated by the nearby sources IGR J16320-4751 and IGR J16358-4726, and we provide information on when these sources were bright and on the nature of their energy spectra.

Tomsick, John A.↗
NASA NTRS2005

X-ray Observations of the Black Hole Transient 4U 1630-47 During 2 Years of X-ray Activity

The black hole candidate (BHC) X-ray transient 4U 1630-47 continuously produced strong X-ray emission for more than 2 years during its 2002-2004 outburst, which is one of the brightest and longest outbursts ever seen from this source. We use more than 300 observations made with the Rossi X-Ray Timing Explorer (RM E) to study the source throughout the outburst, along with hard X-ray images from the International Gamma-Ray Astrophysics Laboratory (INTEGRAL), which are critical for interpreting the RXTE data in this crowded field. The source exhibits extreme behaviors, which can be interpreted as an indication that the system luminosity approaches the Eddington limit. For 15 observations, fitting the spectral continuum with a disk-blackbody plus power-law model results in measured inner disk temperatures between 2.7 and 3.8 key and such temperatures are only rivaled by the brightest BHC systems, such as GRS 1915+105 and XTE 51550-564. If the high temperatures are caused by the dominance of electron scattering opacity in the inner regions of the accretion disk, it is theoretically required that the source luminosity be considerably higher than 20% of the Eddington limit. We detect a variety of high-amplitude variability, including hard 10-100 s flares, which peak at levels as much as 2-3 times higher than nonflare levels. This flaring occurs at the highest disk luminosities in a regime in which the source deviates from the L(sub disk) infinity T(sup 4)(sub in) relationship that is seen at lower luminosities, possibly suggesting that we are seeing transitions between a Shakura & Sunyaev disk and a "slim" disk, which is predicted to occur at very high mass accretion rates. The X-ray properties in 2002-2004 are significantly different from those seen during the 1998 outburst, which is the only outburst with detected radio jet emission. Our results support the "jet line" concept recently advanced by Fender and coworkers. Our study allows for a test of the quantitative McClintock & Remillard spectral state definitions, and we find that these definitions alone do not provide a complete description of the outburst. Finally, for several of the observations, the high-energy emission is dominated by the nearby sources IGR 516320-4751 and IGR 516358-4726, and we provide information on when these sources were bright and on the nature of their energy spectra

Tomsick, John A.↗
NASA NTRS1997

Replicated Wolter-I X-ray Optics for Lightweight, High Angular Resolution, Large Collecting Area X-Ray Telescopes

The next generation of orbiting x-ray observatories will require high angular resolution telescopes that have an order of magnitude greater collecting area in the 0.1-10 keV spectral region than those currently under construction, but with a much lower weight and cost per unit area. Replicated Wolter-I x-ray optics have the potential to meet this requirement. The currently demonstrated capabilities of replicated Wolter-I optics will be described, and a development plan for creating lightweight, high angular resolution, large effective area x-ray telescopes will be presented.

Joy, M.↗
NASA NTRS1997

X-rays and gamma-rays from accretion flows onto black holes in Seyferts and X-ray binaries

Observations and theoretical models of X-ray/gamma ray spectra of radio quiet Seyfert galaxies and Galactic black hole candidates are reviewed. The spectra from these objects share the following characteristics: an underlying power law with a high energy cutoff above 200 keV; a Compton reflection component with a Fe K alpha line, and a low energy absorption by intervening cold matter. The X-ray energy spectral index, alpha, is typically in the range between 0.8 and 1 in Seyfert spectra, and that of the hard state spectra of the black hole candidates Cygnus X-1 and GX 339-4 is typically between 0.6 and 0.8. The Compton reflection component corresponds with cold matter covering a solid angle of between 0.8pi and 2pi as seen from the X-ray source. The broadband spectra of both classes of sources are well fitted by Compton upscattering of soft photons in thermal plasma. The fits yield a thermal plasma temperature of 100 keV and the Thomson optical depth of 1. All the spectra presented are cut off before the electron rest energy 511 keV, indicating that electron/positron pair production is an important process.

Zdziarski, Andrzej A.↗
NASA NTRS2021

Continuum, cyclotron line, and absorption variability in the high-mass X-ray binary Vela X-1

Because of its complex clumpy wind, prominent cyclotron resonant scattering features, intrinsic variability, and convenient physical parameters (close distance, high inclination, and small orbital separation), which facilitate the observation and analysis of the system, Vela X-1 is one of the key systems for understanding accretion processes in high-mass X-ray binaries on all scales. We revisit Vela X-1 with two new observations taken with NuSTAR at orbital phases ∼0.68–0.78 and ∼0.36–0.52, which show a plethora of variability and allow us to study the accretion geometry and stellar wind properties of the system. We follow the evolution of spectral parameters down to the pulse period timescale using a partially covered power law continuum with a Fermi-Dirac cutoff to model the continuum and local absorption. We are able to confirm anti-correlations between the photon index and the luminosity and, for low fluxes, between the folding energy and the luminosity, implying a change of properties in the Comptonising plasma. We were not able to confirm a previously seen correlation between the cyclotron line energy and the luminosity of the source in the overall observation, but we observed a drop in the cyclotron line energy following a strong flare. We see strong variability in absorption between the two observations and within one observation (for the ∼0.36–0.52 orbital phases) that can be explained by the presence of a large-scale structure, such as accretion and photoionisation wakes in the system, and our variable line of sight through this structure.

C. M. Diez↗
NASA NTRS1996

Energetics of impulsive solar flares: Correlating BATSE hard x-ray bursts and the solar atmosphere's soft x-ray response

This investigation has involved the correlation of BATSE-observed solar hard X-ray emission with the characteristics of soft X-ray emitting plasma observed by the Yohkoh Bragg Crystal Spectrometers. The goal was to test the hypothesis that localized electron beam heating is the dominant energy transport mechanism in impulsive flares, as formulated in the thick-target electron-heated model of Brown.

Newton, Elizabeth↗
NASA NTRS1978

On two new X-ray sources in the SMC and the high luminosities of the Magellanic X-ray sources

The discovery of two new X-ray sources, SMC X-2 and SMC X-3, in the Small Magellanic Cloud is reported. They have hard spectra, and their luminosities in the energy range 2-11 keV are 1.0 and 0.7 by 10 to the 38th power erg/sq cm per sec, respectively. It is shown that the luminosity distribution of the known Magellanic X-ray sources, which are now nine in number, is shifted toward higher luminosities with respect to that of similar sources in the Galaxy, and that the cause of the shift is probably an underabundance of heavy elements in the material accreted by the X-ray sources.

Clark, G.↗
NASA NTRS1975

Soft X-ray observations of Centaurus X-3 from Copernicus

We have detected soft X-ray emission from Centaurus X-3 in the 0.6-1.9 keV band, using the focusing telescope aboard OAO Copernicus. The flux is compatible with an extrapolation of the harder X-ray spectrum, attenuated by (3-4) times 10 to the 22nd atoms per sq cm of interstellar and/or circumstellar matter. The data are consistent with the distance estimate of 5-10 kpc derived from the spectroscopic modulus of the optical component, and obviate the need to postulate the primary to be an anomalously subluminous hot star. There is currently no compelling evidence that such models must be invoked to explain any of the observed compact X-ray sources.

Margon, B.↗
NASA NTRS1976

The quantitative properties of three soft X-ray flare kernels observed with the AS&E X-ray telescope on Skylab

The physical parameters for the kernels of three solar X-ray flare events have been deduced using photographic data from the S-054 X-ray telescope on Skylab as the primary data source and 1-8 and 8-20 A fluxes from Solrad 9 as the secondary data source. The kernels had diameters of about 5-7 seconds of arc and in two cases electron densities at least as high as 0.3 trillion per cu cm. The lifetimes of the kernels were 5-10 min. The presence of thermal conduction during the decay phases is used to argue: (1) that kernels are entire, not small portions of, coronal loop structures, and (2) that flare heating must continue during the decay phase. We suggest a simple geometric model to explain the role of kernels in flares in which kernels are identified with emerging flux regions.

Kahler, S. W.↗
NASA NTRS1997

Outbursts from the Transient X-Ray Pulsar Cep X-4 (GS 2138+56)

Cep X-4 was discovered with the Orbiting Solar Observatory (OSO) 7 Satellite in 1973 June-July, but no pulsations were detected. In March 1988, an additional outburst was observed with Gingaq. Pulsations at a period of 66.2490 +/- .0001 s were detected during a month long outburst which peaked at about 100 mCrab (1-20 keV) in early April 1988. The source apparently did not appear again until June 1993 when it was detected by Roentgen Satellite (ROSAT) and Burst and Transient Source Experiment (BATSE). Pulsations at a period of 66.2499 +/- .0007 s were detected by BATSE. The outburst lasted about two weeks and had a peak pulsed flux of 15-20 mCrab (20-50 keV). In July 1997, BATSE and the All-Sky Monitor (ASM) on Rossi X-ray Timing Explorer (RXTE) observed a new outburst from Cep X-4. Pulsations at a period of 66.2743 +/- 0.0005 s were detected by BATSE. This outburst lasted about 2 weeks and peaked at a pulsed flux of about 10-15 mCrab (20-50 keV). Results of a search of BATSE data for additional outbursts will be presented. Pulse frequency and flux histories will be presented and compared to the flux history from the RXTE ASM. Implications of the apparent spin-down between outbursts will be discussed.

Wilson, Colleen A.↗
NASA NTRS2004

X Persei: The X-Ray Halo and Spectrum of a High-Latitude X-Ray Binary

The observations were completed on February 25,2003. Although the source was in the FOV for 31.4 ksec, only 18.2 ksec of data were usable due to a strong flare in the first part of the observations. We have extracted the X-ray halo from the good portion of the data, and were then faced with the problem of calibrating the far-off-axis point spread function, which is needed only for X-ray halo analysis; the same problem affected Chandra halo observations. We used data from 3C273, MCG 6-30-15, LMC X-1, and Her X-1 to measure the PSF, and found that it is reasonably well fit with a power law of the form PSF(theta) = A theta^-G, where A = 0.0034 arcmin^-2, and G = 3.05 for energies between 1-4 keV. This suggests there are fewer large dust grains along the When fitting the spectrum of X Persei, we found NH = 3e21 cm^-2, as expected. However, the X-ray halo (using a Mathis, Rumpl, Nordsieck 1977 dust model) required at most a column density of 1.4+/-0.1 e21 cm^-2; other models required sightline to X Per than would have been expected. In addition, a smoothly distributed dust model fit the observations better than a single cloud model, also against our expectations. We are in the process of writing a paper to be submitted to ApJ with these results, and will also present them at the 2004 HEAD meeting in New Orleans.

Mushotzky, Richard↗
NASA NTRS2026

X-Ray Polarization of Z-Type Neutron Star Low-Mass X-Ray Binaries II. Spectropolarimetric Analysis

IXPE has provided for the first time detailed energy- and time-resolved X-ray polarimetry of Z-type neutron star low-mass X-ray binaries (NS-LMXBs) as they move along their color-color diagrams (CCDs). These sources can reach the highest polarization observed for NS-LXMBs in the 2–8 keV range when they move along the horizontal branch. In a previous paper, we characterized the spectral state of a sample of Z-sources using the CCD and estimated the polarization with model-independent analysis. Here, we present detailed spectropolarimetric analysis for each source on each branch using data from IXPE, NICER, and NuSTAR. The continuum X-ray emission of all the sources is well described with a combination of thermal accretion disk emission plus a harder Comptonized component. In addition, reflection features, in particular the relativistically broadened Fe Kα line, are observed for our sources, except GX 5–1. For most of the sources and branches, the main contribution to the X-ray emission and polarization is due to Comptonization: moving from the horizontal branch (HB) to the normal branch (NB), the polarization degree (PD) in the 2–8 keV band varies from about 6% to 3–4%, while the PD is loosely constrained in the flaring branch (FB), due to the shorter exposures. These PD values are significantly higher than theoretical expectations for typical spreading or boundary layer configurations. The polarization of the disk is generally lower (below 3%) but still higher than predictions for an electron scattering-dominated, plane-parallel atmosphere above the disk observed at the corresponding inclination. Moreover, the polarization angle (PA) of the disk seems to be significantly misaligned and not perpendicular to that of Comptonization. We find no correlation between the polarization signal and the inclination, nor with the contribution of reflected photons throughout the Z-track.

accretion↗
NASA NTRS2015

A Coordinated X-Ray and Optical Campaign of the Nearest Massive Eclipsing Binary, Delta Orionis Aa. II. X-Ray Variability

We present time-resolved and phase-resolved variability studies of an extensive X-ray high-resolution spectral data set of the delta Ori Aa binary system. The four observations, obtained with Chandra ACIS (Advanced CCD Imaging Spectrometer) HETGS (High Energy Transmission Grating), have a total exposure time approximately equal to 479 kiloseconds and provide nearly complete binary phase coverage. Variability of the total X-ray flux in the range of 5-25 angstroms is confirmed, with a maximum amplitude of about plus or minus15 percent within a single approximately equal to125 kiloseconds observation. Periods of 4.76 and 2.04 days are found in the total X-ray flux, as well as an apparent overall increase in the flux level throughout the nine-day observational campaign. Using 40 kiloseconds contiguous spectra derived from the original observations, we investigate the variability of emission line parameters and ratios. Several emission lines are shown to be variable, including S (sub XV), Si (sub XIII), and Ne (sub IX). For the first time, variations of the X-ray emission line widths as a function of the binary phase are found in a binary system, with the smallest widths at phi = 0.0 when the secondary delta Ori Aa2 is at the inferior conjunction. Using 3D hydrodynamic modeling of the interacting winds, we relate the emission line width variability to the presence of a wind cavity created by a wind-wind collision, which is effectively void of embedded wind shocks and is carved out of the X-ray-producing primary wind, thus producing phase-locked X-ray variability.

X-ray flux↗
NASA NTRS1994

10 micron detection of the hard X-ray transient GRO J0422+32: Free-free emission from an X-ray-driven accretion disk wind?

We report the detection of 10 micrometer emission from the transient low-mass X-ray binary (LMXB) and optical nova GRO J0422+32 near the maximum of its outburst. We discuss this result in terms of (1) a 'standard' model according to which low-energy radiation of LMXB is caused by reprocessing of X-rays in an accretion disk; (2) emission from a cool secondary star; (3) emission from dust grains heated by the transient X-rays, and (4) free-free emission from an X-ray-driven wind from the accretion disk. Only the fourth alternative provides a viable explanation for the observed 10 micrometer emission, with a mass-loss rate in the disk wind that may be substantially higher than the rate of accretion onto the compact star. The presence of such a wind may have a profound effect on the evolution of the binary, and contribute to the solution of the 'birthrate problem' of millisecond ratio pulsars.

Paradijs, Van J.↗