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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

X-ray observations of X Persei

The HEAO 2 Einstein Observatory was used to confirm the identification of 4U 0352 + 30 with X Per. The HEAO 2 data were analyzed in order to determine an additional point in the pulse period history of the X-ray source and to search for short binary periods. In addition, a majority of the historical X-ray observations was reanalyzed and more refined values for the pulse period as a function of time were obtained. The period history possess significant scatter, but no evidence for a measurable long-term spin-up trend is found, and hence a lower limit to the spin-up time scale is set. This lower limit is consistent with the presence of a neutron star, but it does not rule out a degenerate dwarf. The period history was also searched for evidence of binary motion, and upper limits to a(x) sin i were obtained.

Weisskopf, M. C.↗
NASA NTRS1996

Design, Fabrication and Testing of Multilayer Coated X-Ray Optics for the Water Window Imaging X-Ray Microscope

Hoover et. al. built and tested two imaging Schwarzschild multilayer microscopes. These instruments were constructed as prototypes for the "Water Window Imaging X-Ray Microscope," which is a doubly reflecting, multilayer x-ray microscope configured to operate within the "water window." The "water window" is the narrow region of the x-ray spectrum between the K absorption edges of oxygen (lamda = 23.3 Angstroms) and of carbon (lamda = 43.62 Angstroms), where water is relatively highly transmissive and carbon is highly absorptive. This property of these materials, thus permits the use of high resolution multilayer x-ray microscopes for producing high contrast images of carbon-based structures within the aqueous physiological environments of living cells. We report the design, fabrication and testing of multilayer optics that operate in this regime.

Spencer, Dwight C.↗
NASA NTRS2003

X-Ray Testing Constellation-X Optics at MSFC's 100-m Facility

In addition to the 530-m-long X-Ray Calibration Facility (XRCF), NASA's Marshall Space Flight Center (MSFC) operates a 104-m-long (source-to-detector) X-ray-test facility. Originally developed and still occasionally used for stray-light testing of visible-fight optical systems, the so-called "Stray-Light Facility" now serves primarily as a convenient and inexpensive facility for performance evaluation and calibration of X-ray optics and detectors. The facility can accommodate X-ray optics up to about 1-m diameter and 12-m focal length. Currently available electron-impact sources at the facility span the approximate energy range 0.2 to 100 keV, thus supporting testing of soft- and hard-X-ray optics and detectors. Available MSFC detectors are a front-illuminated CCD (charge-coupled device) and a scanning CZT (cadmium--zinc--telluride) detector, with low-energy cut-offs of about 0.8 and 3 keV, respectively. In order to test developmental optics for the Constellation-X Project, led by NASA's Goddard Space Flight Center (GSFC), MSFC undertook several enhancements to the facility. Foremost among these was development and fabrication of a five-degree-of-freedom (5-DoF) optics mount and control system, which translates and tilts the user-provided mirror assembly suspended from its interface plate. Initial Constellation-X tests characterize the performance of the Optical Alignment Pathfinder Two (OAP2) for the large Spectroscopy X-ray Telescope (SXT) and of demonstration mirror assemblies for the Hard X-ray Telescope (HXT). With the Centroid Detector Assembly (CDA), used for precision alignment of the Chandra (nee AXAF) mirrors, the Constellation-X SXT Team optically aligned the individual mirrors of the OAPZ at GSFC. The team then developed set-up and alignment procedures, including transfer of the alignment from the optical alignment facility at GSFC to the X-ray test facility at MSFC, using a reference flat and fiducials. The OAPZ incorporates additional ancillary features --- fixed aperture mask and movable sub-aperture mask --- to facilitate X-ray characterization of the optics. Although the OAPZ was designed to- have low sensitivity to temperature offsets and gradients, analyses showed the necessity of active temperature control for the X-ray performance testing. Thus, the Smithsonian Astrophysical Observatory (SAO) implemented a thermal control and monitoring system, designed to hold the OAP2 close to its assembly.

O'Dell, Stephen↗
NASA NTRS2019

Poisson vs. Gaussian statistics for sparse X-ray data: Application to the soft X-ray spectrometer

Reliable results when fitting X-ray data require proper consideration of the statistics involved. We probe the impact of Gaussian versus Poisson statistics at low count levels using both the standard χ^(2) method and maximum likelihood based on Poisson (C) statistics. The difference is studied and quantified through simulated spectra with known properties. We then test the results through analysis of Mn Kα calibration data taken with the flight spare microcalorimeter for the Hitomi soft X-ray spectrometer. Through comparison with simulations, our results show that the χ^(2) method tends to give overly optimistic estimates of the detector energy resolution, in particular when there are few counts. Given an energy resolution of ∼5 eV and a line with about 100 photons, the line width becomes ∼10% lower in the χ^(2) method than in Poisson statistics. This is a consequence of the uncertainties being dominated by counting statistics, and therefore highlights the need to choose the appropriate fit statistic.

Shinya Yamada↗
NASA NTRS1976

Soft X-rays from Her X-1 during the off phase

Weak 0.28-keV radiation was observed from Her X-1 5 days before turn-on in the 35 day cycle. The observations were made from an Aerobee rocket. The 0.28-keV intensity is about 1/25 that observed during the on phase. Some evidence for X-rays above 1 keV is also present, and it is possible that the spectrum is different only in intensity from the spectrum in the on phase. The radiation may be X-rays from the vicinity of the neutron star, scattered by ionized material in the inner accretion disk, or may be thermal radiation from the inner accretion disk, or both.

Fritz, G.↗
NASA NTRS1992

Thermonuclear flash model for long X-ray tails from Aquila X-1

Attention is given to a thermonuclear flash model for long X-ray tails from the recurrent transient Aql X-1, in which the extended phase of nuclear burning is due to the fact that the envelope is out of thermal equilibrium. Only the first X-ray burst emitted by Aql X-1 during its transient outburst exhibits a long X-ray tail. The properties of subsequent bursts are distinguished by a lack of an X-ray tail reflecting the much smaller accumulated masses which result from the effects of thermal inertia in the neutron star envelope. The characteristics of the latter bursts are similar to those of typical X-ray bursters. For a neutron star characterized by a mass and radius of 1.4 solar mass and 9.1 km, respectively, the occurrence of the long X-ray tail requires that the mass of the accumulated layer be less than 10 exp 23 g and that the envelope temperatures of the neutron star be less than 1.5 x 10 exp 7. This interpretation is found to be consistent with the thermal relaxation of the neutron star envelope during the quiescent state of Aql X-1 and with the mass accretion rates inferred for the transient outburst itself.

Fushiki, Ikko↗
NASA NTRS2018

Multi-Parameter Nonlinear Gain Correction of X-Ray Transition Edge Sensors for the X-Ray Integral Field Unit

With its array of 3840 Transition Edge Sensors (TESs), the Athena X-ray Integral Field Unit (X-IFU) will provide spatially resolved high-resolution spectroscopy (2.5 eV up to 7 keV) from 0.2 to 12 keV, with an absolute energy scale accuracy of 0.4 eV. Slight changes in the TES operating environment can cause significant variations in its energy response function, which may result in systematic errors in the absolute energy scale. We plan to monitor such changes at pixel level via onboard X-ray calibration sources and correct the energy scale accordingly using a linear or quadratic interpolation of gain curves obtained during ground calibration. However, this may not be sufficient to meet the 0.4 eV accuracy required for the XIFU. In this contribution, we introduce a newtwo-parameter gain correction technique, based on both the pulse-height estimate of a fiducial line and the baseline value of the pixels. Using gain functions that simulate ground calibration data, we show that this technique can accurately correct deviations in detector gain due to changes in TES operating conditions such as heat sink temperature, bias voltage, thermal radiation loading and linear amplifier gain. We also address potential optimisations of the onboard calibration source and compare the performance of this new technique with those previously used.

Cucchetti, E.↗
NASA NTRS1994

Search for inverse Compton x-rays from the lobes of Fornax A x-rays from radio galaxies straddling the Fanaroff-Riley transition

Two related studies of radio galaxies are covered in this report. The first is a search for inverse Compton x-rays from the lobes of Fornax A. In this study, a ROSAT position sensitive proportional counter image of Fornax A (NGC 1316) is presented, and after image processing, it was observed that the x-ray emission closely mimicked the radio emission. A second study involved x-rays from radio galaxies straddling the Fanaroff-Riley transition which divides radio galaxies into two broad morphological groups based on whether the lobe radio power is greater or less than a critical value. ROSAT HRI observations were obtained from four bright radio galaxies around the transition to search for x-ray indications of either nuclear engine or ambient medium differences.

Feigelson, Eric D.↗
NASA NTRS1989

Soft X-ray emission lines from low-mass X-ray binaries. I - Collision-dominated models

The soft X-ray line emission from five low-mass X-ray binaries observed by the Einstein Observatory (HEAO 2) Objective Grating Spectrometer is examined. Observed spectra are fitted to model spectra consisting of emission from an optically thin plasma. Fits are performed using a variety of different assumptions for elemental abundances, heating and ionization mechanisms, and the distribution of gas temperature and ionization parameter. The results are discussed in the context of current models for the accretion flow in low-mass X-ray binaries.

Kallman, T. R.↗
NASA NTRS1976

Uhuru observations of an X-ray burst at high galactic latitude centered on the X-ray globular cluster NGC 1851

An X-ray burst from a 0.5 x 10 deg region centered near NGC 1851 (MX 0513-40) was detected in observations made with the Uhuru X-ray observatory on September 19, 1972. The source was observed for 15 seconds with a peak rate of 0.5 that of the Crab (2-6 keV) and was not detected above 0.01 of the Crab in observations 4.5 minutes before or after this event. During the observation, the spectrum developed a low-energy cutoff. NGC 1851 is the second globular cluster identified as a source of X-ray bursts, which suggests that all X-ray bursts may originate in globular clusters, some of which may be optically obscured.

Forman, W.↗
NASA NTRS1986

Simultaneous X-ray and optical observations of GX 339-4 in an X-ray high state

Optical emission, soft X-rays, and hard X-rays have been observed simultaneously from the black hole candidate GX 3339-4 in a typical high state. Each of these components is interpreted as arising from a characteristic region of the accretion disk. Considered as a black hole, GX 339-4 lacks the variable 2 keV blackbody component that would be emitted from the 'solid' surface of a neutron star in the low-mass neutron star binaries. The X-ray emission in the high state is therefore extremely soft and stable in time. The intermediate disk region is optically thick and geometrically thin. The observed soft X-ray component with a 'disk blackbody' spectrum comes from this region. The innermost disk region is dynamically unstable due to the effect of general relativity and possibly due to radiation pressure. This region is responsible for the generation of the hard X-ray tail through Comptonization.

Makishima, K.↗
NASA NTRS1983

Thermal and nonthermal phenomena in solar flare loops at 20 cm wavelength and in X-rays

X-ray images from the P78-1 satellite are presented for a long-lasting burst at 20 cm wavelength mapped with the Very Large Array on May 19, 1979. The decimeter wave observations were originally interpreted in terms of two models, one invoking thermal electrons radiating at low harmonics of the gyrofrequency, and the other invoking mildly relativistic electrons emitting gyrosynchrotron radiation. If the 20 cm source is thermal, it should also be visible in soft X-rays, while if it is nonthermal, the soft X-ray emission should be weak or spatially or temporally distinct from the 20 cm burst. It is found that only one of the three 20 cm sources was approximately co-spatial with the soft X-ray source, and that it was only partially thermal. The 20 cm burst is therefore primarily decimeter type IV emission from mildly relativistic electrons of the post-flare phase. The over 2 hr lifetime and smooth temporal variation of the burst belie its nonthermal nature and suggest continuous acceleration as well as long-term storage of energetic electrons.

Schmahl, E. J.↗
NASA NTRS2012

Swift-X-Ray Telescope Monitoring of the Candidate Supergiant Fast X-ray Transient IGR J16418-4532

We report on the Swift monitoring of the candidate supergiant fast X-ray transient (SFXT) IGR J16418−4532, for which both orbital and spin periods are known (approx. 3.7 d and approx.1250 s, respectively). Our observations, for a total of approx. 43 ks, span over three orbital periods and represent the most intense and complete sampling of the light curve of this source with a sensitive X-ray instrument. With this unique set of observations, we can address the nature of this transient. By applying the clumpy wind model for blue supergiants to the observed X-ray light curve, and assuming a circular orbit, the X-ray emission from this source can be explained in terms of the accretion from a spherically symmetric clumpy wind, composed of clumps with different masses, ranging from approx. 5 × 10(exp 16) to 10(exp 21) g. Our data suggest, based on the X-ray behaviour, that this is an intermediate SFXT.

transient↗