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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 451 records · Page 25
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NASA NTRS2016

The Athena X-ray Integral Field Unit (X-IFU)

The X-ray Integral Field Unit (X-IFU) on board the Advanced Telescope for High-ENergy Astrophysics (Athena) will provide spatially resolved high-resolution X-ray spectroscopy from 0.2 to 12 keV, with 5 pixels over a field of view of 5 arc minute equivalent diameter and a spectral resolution of 2.5 eV up to 7 keV. In this paper, we first review the core scientific objectives of Athena, driving the main performance parameters of the X-IFU, namely the spectral resolution, the field of view, the effective area, the count rate capabilities, the instrumental background. We also illustrate the breakthrough potential of the X-IFU for some observatory science goals. Then we brie y describe the X-IFU design as defined at the time of the mission consolidation review concluded in May 2016, and report on its predicted performance. Finally, we discuss some options to improve the instrument performance while not increasing its complexity and resource demands (e.g. count rate capability, spectral resolution). (2016) .

Space telescopes↗
NASA NTRS1975

Observations of the structure and evolution of solar flares with a soft X-ray telescope

Soft X ray flare events were observed with the S-056 X-ray telescope that was part of the ATM complement of instruments aboard SKYLAB. Analyses of these data are reported. The observations are summarized and a detailed discussion of the X-ray flare structures is presented. The data indicated that soft X-ray emitted by a flare come primarily from an intense well-defined core surrounded by a region of fainter, more diffuse emission. An analysis of flare evolution indicates evidence for preliminary heating and energy release prior to the main phase of the flare. Core features are found to be remarkably stable and retain their shape throughout a flare. Most changes in the overall configuration seem to be result of the appearance, disappearance or change in brightness of individual features, rather than the restructuring or reorientation of these features. Brief comparisons with several theories are presented.

Vorpahl, J. A.↗
NASA NTRS1972

Developable Images Produced by X-rays Using the Nickel Hypophosphite System. 1 X-ray Sensitive Salts

Twenty-eight crystalline salts were X-irradiated and treated with an ammoniacal nickel hypophosphite solution. Treatment (development) of six of the salts resulted in precipitation of nickel metal. The developable salts were four hypophosphites, sodium phosphite, and nickel formate. A mechanism is proposed for the process based on the postulate that micro amounts of hydrogen atoms are formed during the radiation step. During development, these hydrogen atoms cause the formation of nucleation sites of nickel metal. In turn, these sites catalyze further reduction of the nickel cations by the hypophosphite. The results are discussed in terms of application of the process to the formation of developable latent images.

May, C. E.↗
NASA NTRS1981

Rapid X-ray and optical flares from Scorpius X-1

A 1 second time structure in X-ray flares from Sco X-1 and simultaneous optical flares with time structures no faster than 20 s are reported. The shortest reported time scale in the X-ray emission from Sco X-1 is decreased by a factor of 10, while remaining consistent with the parameters of the standard plasma model from Sco X-1. Different mechanisms for the production of X-ray flares and optical flares are suggested, and the production of optical flares by reprocessing on the surface of the binary companion of Sco X-1 is ruled out by the X-ray/optical flare time delay.

Petro, L. D.↗
NASA NTRS1980

The 1978 X-ray and optical outburst of Aquila X-1 /4U 1908+00/

During the summer of 1978 the recurrent transient X-ray source, Aquila X-1, underwent its first major outburst in two years. This paper presents the results of extensive X-ray and optical observations of this event, which lasted for about two months. The peak X-ray luminosity was about 1.3 times that of the Crab and exhibited spectrum-dependent flickering on time scales of about 5 minutes. In addition, one very large flare was observed about one month after maximum that was also correlated with spectral changes. During this flare the previously identified optical counterpart brightened from V = 19 to a peak of V = 14.8, where it was distinctly blue (U - B = 0.4), and then reddened during the decay. These observations are interpreted in terms of a standard accretion disk model with particular emphasis on the similarities to Sco -1 and other dwarf X-ray systems.

Charles, P. A.↗
NASA NTRS1975

Relation of large-scale coronal X-ray structure and cosmic rays. I - Sources of solar wind streams as defined by X-ray emission and H-alpha absorption features

The large-scale structure of the corona and the interplanetary medium during Carrington rotations 1601-1607 is discussed relative to recurrent high-speed solar wind streams and their coronal sources. Only streams A, C, D, and F recur on more than one rotation. Streams A and D are associated with coronal holes, while C and F originate in the high corona (20-50 solar radii) over faint X-ray emissions. The association of the streams with holes is confirmed by earlier findings that there are no large equatorial holes without an associated high-speed stream and that the area of the equatorial region of coronal holes is highly correlated with the maximum velocity observed in the associated stream near 1 AU.

Krieger, A. S.↗
NASA NTRS1986

Quasar evolution and luminosity function - An X-ray perspective

X-ray properties of optically selected QSOs are reviewed, and their implications for the QSO evolution and luminosity function are summarized. Analyses of the explicit dependence of the X-ray to optical luminosity ratio parameter alpha (a,x) on redshift z and optical luminosity Lo are described, and results from a recent analysis of complete, magnitude-limited samples of optically selected QSOs are presented. It is shown that probably all optically-selected QSOs are X-ray loud and that comparisons of the optical evolution and luminosity function, combined with the alpha(o,x)(z,Lo) dependence, with X-ray-selected samples are numerically sensitive to the details of the input.

Avni, Y.↗
NASA NTRS2013

Magnetic Untwisting in Most Solar X-Ray Jets

From 54 X‐ray jets observed in the polar coronal holes by Hinode's X‐Ray Telescope (XRT) during coverage in movies from Solar Dynamic Observatory's Atmospheric Imaging Assembly (AIA) taken in its He II 304 Å band at a cadence of 12 s, we have established a basic characteristic of solar X‐ray jets: untwisting motion in the spire. In this presentation, we show the progression of few of these X‐ray jets in XRT images and track their untwisting in AIA He II images. From their structure displayed in their XRT movies, 19 jets were evidently standard jets made by interchange reconnection of the magnetic‐arcade base with ambient open field, 32 were evidently blowout jets made by blowout eruption of the base arcade, and 3 were of ambiguous form. As was anticipated from the >10,000 km span of the base arcade in most polar X‐ray jets and from the disparity of standard jets and blowout jets in their magnetic production, few of the standard X‐ray jets (3 of 19) but nearly all of the blowout X‐ray jets (29 of 32) carried enough cool (T is approximately 105 K) plasma to be seen in their He II movies. In the 32 X‐ray jets that showed a cool component, the He II movies show 10‐100 km/s untwisting motions about the axis of the spire in all 3 standard jets and in 26 of the 29 blowout jets. Evidently, the open magnetic field in nearly all blowout X‐ray jets and probably in most standard X‐ray jets carries transient twist. This twist apparently relaxes by propagating out along the open field as a torsional wave. High‐resolution spectrograms and Dopplergrams have shown that most Type‐II spicules have torsional motions of 10‐30 km/s. Our observation of similar torsional motion in X‐ray jets strengthens the case for Type‐II spicules being made in the same way as X‐ray jets, by blowout eruption of a twisted magnetic arcade in the spicule base and/or by interchange reconnection of the twisted base arcade with the ambient open field. This work was funded by NASA's Heliophysics Division through its LWS TRT Program and its Hinode Project, and by NSF through its Research Experience for Undergraduates Program.

Moore, Ronald↗
NASA NTRS1978

Extended X-ray observations of Scorpius X-1 with a Bragg crystal spectrometer

Observations covering multiple orbital periods of the X-ray source Sco X-1 were carried out in 1975 and 1976 with the graphite crystal spectrometer aboard OSO 8. Time-averaged continuum spectra are featureless and are reasonably well described in terms of a Comptonized thermal bremsstrahlung spectrum in which kT is about 1.5-2 keV and in which the number of electron scatterings that each photon is assumed to have undergone is of the order of 100. Line limits, typically with equivalent widths of a few electron volts, are established for important emission lines of Si XIII, Si XIV, S XV, S XVI, and Fe XXV as a function of binary phase.

Long, K. S.↗