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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

First Peek of ASTRO-H Soft X-Ray Telescope (SXT) In-Orbit Performance

ASTRO-H (Hitomi) is a Japanese X-ray astrophysics satellite just launched in February, 2016, from Tanegashima, Japan by a JAXA's H-IIA launch vehicle. It has two Soft X-ray Telescopes (SXTs), among other instruments, that were developed by the NASA Goddard Space Flight Center in collaboration with ISAS/JAXA and Nagoya University. One is for an X-ray micro-calorimeter instrument (Soft X-ray Spectrometer, SXS) and the other for an X-ray CCD camera (Soft X-ray Imager, SXI), both covering the X-ray energy band up to 15 keV. The two SXTs were fully characterized at the 30-m X-ray beam line at ISAS/JAXA. The combined SXT+SXS system effective area is about 250 and 300 cm(exp 2) at 1 and 6 keV, respectively, although observations were performed with the gate valve at the dewar entrance closed, which blocks most of low energy X-rays and some of high energy ones. The angular resolution for SXS is 1.2 arcmin (Half Power Diameter, HPD). The combined SXT+SXI system effective area is about 370 and 350 cm (exp 2) at 1 and 6 keV, respectively. The angular resolution for SXI is 1.3 arcmin (HPD). The both SXTs have a field of view of about 16 arcmin (FWHM of their vignetting functions).The SXT+SXS field of view is limited to 3 x 3 arcmin by the SXS array size. In-flight data available to the SXT team was limited at the time of this conference and a point-like source data is not available for the SXT+SXS. Although due to lack of attitude information we were unable to reconstruct a point spread function of SXT+SXI, according to RXJ1856.5-3754 data, the SXT seems to be working as expected in terms of imaging capability. As for the overall effective area response for both SXT+SXS and SXT+SXI, consistent spectral model fitting parameters with the previous measurements were obtained for Crab and G21.5-0.9 data. On the other hand, their 2-10 keV fluxes differ by about 20% at this point. Calibration work is still under progress. The SXT is the latest version of the aluminum foil X-ray mirror, which is extremely light-weight and very low cost, yet produces large effective area over a wide energy-band. Its area-mass ratio is the largest, 16 cm(exp 2)/kg, among ASTRO-H, Chandra, and XMM-Newton mirrors. The aluminum foil mirror is a still compelling technology depending on the mission science goal.

X-rays↗
NASA NTRS2010

Ultrasonic Characterization of Interfaces in Composite Bonds

The inverse determination of imperfect interfaces from reflection spectra of normal and oblique incident ultrasonic waves in adhesive bonds of multidirectional composites is investigated. The oblique measurements are complicated by the highly dispersed nature of oblique wave spectra at frequencies above 3MHz. Different strategies for bond property reconstruction, including a modulation method, are discussed. The relation of measured interfacial spring density to the physico-chemical model of a composite interface described by polymer molecular bonds to emulate loss of molecular strength on an adhesive composite interface is discussed. This potentially relates the interfacial (adhesion) strength (number of bonds at the adhesive substrate interface) to the spring constant (stiffness) area density (flux), which is an ultrasonically measurable parameter.

Wang, N.↗
NASA NTRS1976

Fine Structure in 3C 120 and 3C 84

Seven epochs of very long baseline radio interferometric observations of the Seyfert galaxies 3C 120 and 3C 84, at 3.8-cm wave length using stations at Westford, Massachusetts, Goldstone, California, Green Bank, West Virginia, and Onsala, Sweden, have been analyzed for source structure. An algorithm for reconstructing the brightness distribution of a spatially confined source from fringe amplitude and so called closure phase data has been developed and successfully applied to artificially generated test data and to data on the above mentioned sources. Over the two year time period of observation, 3C 120 was observed to consist of a double source showing apparent super relativistic expansion and separation velocities. The total flux changes comprising one outburst can be attributed to one of these components. 3C 84 showed much slower changes, evidently involving flux density changes in individual stationary components rather than relative motion.

Hutton, L. K.↗
NASA NTRS2012

Multiscale Studies of the Three-Dimensional Dayside X-Line

We review recent experience from the Cluster, Double Star, and THEMIS missions for lessons that apply to the upcoming Magnetospheric Multiscale Mission (MMS) being developed for launch in 2014. On global scales, simulation and statistical studies lead to mean congurations of dayside reconnection, implying specific relative alignments of the inflow magnetic fields and X-line, with implications for MMS operations designed to maximize the number of close encounters with the diffusion region. At intermediate MHD-to-ion scales, reconstruction of features created by one or two X-lines have developed to the point where data from a cluster of spacecraft can determine their temporal trends and the approximate three-dimensional X-line structure. Recent petascale particle-in-cell (PIC) simulations of reconnection encompass three spatial dimensions with excellent resolution, and make striking predictions of electron scale physics that creates complex interacting flux ropes under component reconnection. High time resolution measurements from MMS will determine the detailed electron scale kinetics embedded within the global and MHDion scale contexts. These developments will lead to the refinement of our three-dimensional multiscale picture of reconnection, yielding improved understanding of the global, MHD, and local physics controlling the onset or quenching, variability, and mean rate of reconnection. This in turn will enable improved predictability of the structural features created by transient reconnection, and their space weather consequences.

Reconnection↗
NASA NTRS2002

Simulation of Energy Response of the ATIC Calorimeter

ATIC (Advanced Thin Ionization Calorimeter) is a balloon borne experiment designed to measure the cosmic ray composition for elements from hydrogen to iron and their energy spectra from approx.50 GeV to near 100 TeV. It consists of a Si-matrix detector to determine the charge of a CR particle, a scintillator hodoscope for tracking, carbon interaction targets and a fully active BGO calorimeter. ATIC had its first flight from McMurdo, Antarctica from 28/12/2000 to 13/01/2001. The ATIC flight collected approximately 25 million events. For reconstruction of primary spectra from spectra of energy deposits measured in the experiment, correlations between kinetic energy of a primary particle E(sub kin) and energy deposit in the calorimeter E(sub d) should be known. For this purpose, simulations of energy response of the calorimeter on energy spectra of different nuclei were done. The simulations were performed by GEANT-3.21 code with QGSM generator for nucleus - nucleus interactions. The incident flux was taken as isotropic in the ATIC aperture. Primary spectra power-law by momentum were used as inputs according to standard models of cosmic ray acceleration. These spectra become power-law by kinetic energy at E(sub kin) higher than approx.20Mc(sup 2), where M is primary nucleus mass. It should be noted that energy deposit spectra measured by ATIC illustrate similar behavior. Distributions of ratio E(sub kin)/E(sub d) are presented for different energy deposits and for a set of primaries. For power-law regions of energy spectra at E(sub d)> or equal to 20Mc(sup 2) the obtained mean value of E(sub kin)/E(sub d) increases from approx.2.4 for protons to approx.3.1 for iron, while rms/ decreases from 50% for protons to about 15% for iron. These values were obtained for the spectral index gamma=1.6

Batkov, K. E.↗
NASA NTRS2011

Relation Between the 3D-Geometry of the Coronal Wave and Associated CME During the 26 April 2008 Event

We study the kinematical characteristics and 3D geometry of a large-scale coronal wave that occurred in association with the 26 April 2008 flare-CME event. The wave was observed with the EUVI instruments aboard both STEREO spacecraft (STEREO-A and STEREO-B) with a mean speed of approx 240 km/s. The wave is more pronounced in the eastern propagation direction, and is thus, better observable in STEREO-B images. From STEREO-B observations we derive two separate initiation centers for the wave, and their locations fit with the coronal dimming regions. Assuming a simple geometry of the wave we reconstruct its 3D nature from combined STEREO-A and STEREO-B observations. We find that the wave structure is asymmetric with an inclination toward East. The associated CME has a deprojected speed of approx 750 +/- 50 km/s, and it shows a non-radial outward motion toward the East with respect to the underlying source region location. Applying the forward fitting model developed by Thernisien, Howard, and Vourlidas we derive the CME flux rope position on the solar surface to be close to the dimming regions. We conclude that the expanding flanks of the CME most likely drive and shape the coronal wave.

CMEs↗
NASA NTRS2013

Time Variations of Cosmic-Ray Helium Isotopes with BESS-Polar I

The Balloon-borne Experiment with a Superconducting Spectrometer (BESS) is configured with a solenoidal superconducting magnet and a suite of precision particle detectors, including time-of-flight hodoscopes based on plastic scintillators, a silica-aerogel Cherenkov detector, and a high resolution tracking system with a central jet-type drift chamber. The charges of incident particles are determined from energy losses in the scintillators. Their magnetic rigidities (momentum/charge) are measured by reconstructing each particle trajectory in the magnetic field, and their velocities are obtained by using the time-of-flight system. Together, these measurements can accurately identify helium isotopes among the incoming cosmic-ray helium nuclei up to energies in the GeV per nucleon region. The BESS-Polar I instrument flew for 8.5 days over Antarctica from December 13th to December 21st, 2004. Its long-duration flight and large geometric acceptance allow the time variations of isotopic fluxes to be studied for the first time. The time variations of helium isotope fluxes are presented here for rigidities from 1.2 to 2.5 GV and results are compared to previously reported proton data and neutron monitor data.

Cosmic-ray flux time variations↗
NASA NTRS2024

The Mega-MUSCLES Treasury Survey: X-Ray to Infrared Spectral Energy Distributions of a Representative Sample of M Dwarfs

We present 5–1 × 107 Å spectral energy distributions (SEDs) for 12 M dwarf stars covering spectral types M0–M8. Our SEDs are provided for community use as a sequel to the Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems (MUSCLES) survey. The 12 stars include eight known exoplanet hosts and four stars chosen to fill out key parameter space in spectral type and rotation period. The SEDs are constructed from Hubble Space Telescope ultraviolet spectroscopy and XMM Newton, Chandra, and/or Swift X-ray observations, and completed with various model data, including Lyα reconstructions, PHOENIX optical models, APEC coronal models, and differential emission measure models in the currently-unobservable extreme ultraviolet. We provide a complete overview of the Mega-MUSCLES program, including a description of the observations, models, and SED construction. The SEDs are available as MAST high-level science products and we describe the various data products here. We also present ensemble measurements from our sample that are of particular relevance to exoplanet science, including the high-energy fluxes in the habitable zone and the farultraviolet to near-ultraviolet ratio. Combined with MUSCLES, Mega-MUSCLES provides SEDs covering a wide range of M dwarf spectral types and ages such that suitable proxies for any M dwarf planet host of interest may be found in our sample. However, we find that ultraviolet and X-ray fluxes can vary even between stars with similar parameters, such that observations of each exoplanet host star will remain the gold standard for interpreting exoplanet atmosphere observations.

David J. Wilson↗
NASA NTRS1996

Magnetopause Transects

A novel method is described for reconstruction of two-dimensional current-layer structures from measurements taken by a single spacecraft traversing the layer. In its present form, the method is applicable only to 2D magnetohydrostatic structures that are passively convected past the observing spacecraft. It is tested on a magnetopause crossing of the tangential-discontinuity type by the spacecraft AMPTE/IRM. The magnetic structures recovered include a magnetic island located between two X-type nulls as well as a magnetic 'worm hole' through which a bundle of weak magnetic flux appears to connect the magnetosphere and the magnetosheath.

Sonnerup, B. U. O↗
NASA NTRS2003

CIZA: The First Systematic X-Ray Search for Clusters of Galaxies Behind the Milky Way

The aim of the CIZA project (Clusters In the Zone of Avoidance) was to take the first step toward a complete X-ray census of clusters of galaxies behind the plane of the Galaxy (the absolute value of b less than or equal to 20 degrees), the historical Zone of Avoidance of optical extragalactic surveys. Finding these heavily obscured clusters in ROSAT All-Sky Survey data would allow us to: 1. Construct the first truly all-sky, statistically complete, X-ray flux limited sample of galaxy clusters; 2. Use this sample to obtain an improved measurement of the cluster dipole (both amplitude and direction); 3. Chart large-scale structure across the plane of the Milky Way as traced by galaxy clusters; 4. Identify potential massive galaxy clusters contributing to the observed large-scale flow pattern in the local universe, specifically in the region around the Great Attractor; and 5. Use least-action modelling to deduce the gravitational fields created by galaxy clusters and compare this reconstruction with the one obtained from local galaxy surveys. Our project was highly successful in demonstrating the feasibility of this undertaking and allowed substantial progress toward achieving the stated science goals.

Ebeling, Harald↗
NASA NTRS1988

Late Pleistocene variations in Antarctica sea ice. I - Effect of orbital isolation changes. II - Effect of interhemispheric deep-ocean heat exchange

A dynamic-thermodynamic sea-ice model is presently used to ascertain the effects of orbitally-induced insolation changes on Antarctic sea-ice cover; the results thus obtained are compared with modified CLIMAP reconstructions of sea-ice 18,000 years ago. The minor influence exerted by insolation on Pleistocene sea-ice distributions is attributable to a number of factors. In the second part of this investigation, variations in the production of warm North Atlantic Deep Water are proposed as a mechanism constituting the linkage between climate fluctuations in the Northern and Southern hemispheres during the Pleistocene; this hypothesis is tested by examining the sensitivity of the dynamic-thermodynamic model for Antarctic sea-ice changes in vertical ocean heat flux, and comparing the simulations with modified CLIMAP sea-ice maps for 18,000 years ago.

Crowley, Thomas J.↗
NASA NTRS1998

Beta in Streamers

Streamers are generally described as regions of the corona in which the density is higher than in coronal holes because the plasma is trapped by closed loops of magnetic flux. In contrast, MHD models of the global corona show the plasma beta in streamers above siml.2R_S (heliocentric). There are three recent contributions to this topic. The first is that heating near the cusp further drives beta up and results in release of new slow solar wind plasma from the top of the streamer. The second is SOHO/UVCS observations, in combination with a potential field/source surface model of the magnetic field, that show beta above 1.2R_S in a streamer observed near solar sunspot minimum. The third is a magnetic field reconstruction technique that uses field deforming algorithms and is more versatile for local fields than potential field models . The field reconstruction algorithm was applied to an isolated active region (AR 7999) and to the Pneuman Kopp global MHD model (beta has never been published for their model). In the active region, beta becomes larger than unity at siml.2 R_S. In the Pneuman & Kopp model, beta at the base of the streamer and rises with increasing height, becoming 15-20 at 1.6R_S and 35- 50 at 1.7R_S. Global simulations go on to show that the reason streamers do not simply explode under such high beta conditions is that they are held down by pressure from the sides due to the magnetic fields (and low beta) in adjacent coronal holes. The main role of the closed magnetic loop near the cusp is to keep the steamer from continuously leaking plasma, as otherwise happens in a magnetic pinch which is similar but has no closed loops. Awareness of MHD physical conditions in streamers is causing us to focus more attention on the details of the heating. On obvious suggestion is that heating is at much lower heights in streamers than in coronal holes. Also, energy which is directly delivered as momentum in coronal holes might all be deposited as heat in streamers.

Suess, Steven T.↗
NASA NTRS2022

Measurement of Galactic 26Al with the Compton Spectrometer and Imager

The Compton Spectrometer and Imager (COSI) is a balloon-borne compact Compton telescope de-17signed to survey the 0.2–5 MeV sky. COSI’s energy resolution of ∼0.2% at 1.8 MeV, single-photon reconstruction, and wide field of view make it capable of studying astrophysical nuclear lines, particularly the 1809 keVγ-ray line from decaying Galactic 26Al. Most 26Al originates in massive stars and core-collapse supernova nucleosynthesis, but the path from stellar evolution models to Galaxy-wide emission remains unconstrained. In 2016, COSI had a successful 46-day flight on a NASA super pressure balloon. Here, we detail the first search for the 1809 keV26Al line in the COSI 2016 balloon flight using a maximum likelihood analysis. We find a Galactic 26Al flux of (8.6±2.5) ×10−4ph cm−2s−124 within the Inner Galaxy (|ℓ|≤30◦,|b|≤10◦) with 3.7σ significance above background. Within uncertainties, this flux is consistent with expectations from previous measurements by SPI and COMPTEL. This analysis demonstrates COSI’s powerful capabilities for studies of γ-ray lines and underscores the scientific potential of future compact Compton telescopes. In particular, the next iteration of COSI as a NASA Small Explorer satellite has recently been approved for launch in 2025.

Gamma-ray lines↗
NASA NTRS2012

Middle Atmosphere Response to Different Descriptions of the 11-Year Solar Cycle in Spectral Irradiance in a Chemistry-Climate Model

The 11-year solar cycle in solar spectral irradiance (SSI) inferred from measurements by the SOlar Radiation & Climate Experiment (SORCE) suggests a much larger variation in the ultraviolet than previously accepted. We present middle atmosphere ozone and temperature responses to the solar cycles in SORCE SSI and the ubiquitous Naval Research Laboratory (NRL) SSI reconstruction using the Goddard Earth Observing System chemistry-climate model (GEOS CCM). The results are largely consistent with other recent modeling studies. The modeled ozone response is positive throughout the stratosphere and lower mesosphere using the NRL SSI, while the SORCE SSI produces a response that is larger in the lower stratosphere but out of phase with respect to total solar irradiance above 45 km. The modeled responses in total ozone are similar to those derived from satellite and ground-based measurements, 3-6 Dobson Units per 100 units of 10.7-cm radio flux (F10.7) in the tropics. The peak zonal mean tropical temperature response 50 using the SORCE SSI is nearly 2 K per 100 units 3 times larger than the simulation using the NRL SSI. The GEOS CCM and the Goddard Space Flight Center (GSFC) 2-D coupled model are used to examine how the SSI solar cycle affects the atmosphere through direct solar heating and photolysis processes individually. Middle atmosphere ozone is affected almost entirely through photolysis, whereas the solar cycle in temperature is caused both through direct heating and photolysis feedbacks, processes that are mostly linearly separable. Further, the net ozone response results from the balance of ozone production at wavelengths less than 242 nm and destruction at longer wavelengths, coincidentally corresponding to the wavelength regimes of the SOLar STellar Irradiance Comparison Experiment (SOLSTICE) and Spectral Irradiance Monitor (SIM) on SORCE, respectively. A higher wavelength-resolution analysis of the spectral response could allow for a better prediction of the atmospheric response to arbitrary SSI variations.

Swartz, W. H.↗
NASA NTRS1992

Underground muons from the direction of Cygnus X-3

The flux of underground muons from the direction of the binary Cygnus X-3 was measured by the Soudan 2 proton decay detector. This time-projection calorimeter is located at a depth of 2200 m (water equivalent) in northern Minnesota at latitude 48 deg N, longitude 92 deg W. An analysis was then performed that compared both the total observed flux and the observed flux per transit with the number of events expected in the absence of a source. This expected number of events was determined by combining the detector acceptance as a function of time with detector acceptance as a function of the local spatial coordinates. These functions were evaluated by use of off-source events. The direction of Cygnus X-3 was defined as a 2 deg half-angle cone, centered on the nominal source coordinates. This definition is consistent with the expected appearance of a point source in the Soudan 2 detector after consideration of track reconstruction errors, multiple scattering in the rock, and possible systematic effects. Details of the analysis and the results are presented.

Marshak, M. L.↗
NASA NTRSDate not supplied

Modeling the Effective Elasticity of Anisotropic Porous Materials

The development and optimization of composite materials designed for thermal protection of NASA’s spacecraft require understanding their physical response to high-enthalpy environments. To predict their macro-scale properties and behavior, high-fidelity 3D simulations are performed at the microscale on realistic representations of these composites. The digital microstructures are generated either synthetically or through X-ray micro-computed tomography reconstructions. One of the main challenges in the prediction of the structural response of heatshield materials is the computation of the effective elasticity of the fibrous composite, as well as the understanding of the deformation and stresses generated at the microscale. These are driven by the fiber layout within the microstructure and the distribution of the infused matrix. In this effort, the micro-mechanical linear elastic behavior of fibrous ablators is modeled using a numerical method based on the Multi-Point Stress Approximation (MPSA) finite volume scheme, a generalization of the more commonly used Multi-Point Flux Approximation (MPFA) that was presented at the 10th Ablation Workshop. To predict the behavior of fibrous and woven architectures, algorithms that compute the local fiber orientation are used. The implementation of the MPSA was verified using analytical solutions, engineering test cases, and compared against legacy Finite Element Analysis (FEA) software. The stress analysis models were then applied to real geometries used by NASA in thermal protection systems such as fibrous preforms and woven materials and the results were compared to experimental data.

Elasticity↗
NASA NTRS2023

A Data Set of Monthly Freshwater Fluxes From the Greenland Ice Sheet’s Marine-Terminating Glaciers on A Glacier–Basin Scale 2010–2020

The loss of mass from the Greenland ice sheet causes an increasing influx of freshwater to the Greenlandic fjords and the oceans. Freshwater fluxes from marine-terminating glaciers are important to understand fjord circulation and ecosystem dynamics. Here, we present a data set constructed by reformulating existing products into a shared temporal and spatial framework. We combine three publicly available data sets of solid-ice discharge (iceberg), liquid-surface runoff (runoff) and basal melt to present a cohesive overview of the flow of freshwater from marine-terminating glaciers to the Greenlandic fjords. We also calculate glacier drainage basins and compare our findings to previous studies showing that drainage-basin sizes may vary considerably depending on how they were reconstructed. The data set will be a valuable asset to oceanographic, glaciological and marine biological research activities.

Ice mass loss↗
NASA NTRSDate not supplied

Computing the effective elasticity of anisotropic porous media from X-ray computed micro-tomography images

Development and optimization of composite materials designed for thermal protection of NASA’s spacecraft requires the understanding of their physical response to high-enthalpy environments. To predict their macro-scale properties and behavior, high-fidelity 3D simulations are performed at the micro-scale on realistic representations of these composites. The digital micro-structures are generated either synthetically or through X-ray micro-tomography reconstructions. One of the main challenges in the prediction of heatshield material structural response is the computation of the effective elasticity of the fibrous composite, as well as the understanding of the deformation and stresses generated at the micro-scale. These are driven by the fiber layout within the micro-structure and the distribution of the infused matrix. In this effort, the micro-mechanical linear elastic behavior of fibrous ablators is modeled through the use of a numerical method based on the Multi-Point Stress Approximation (MPSA) finite volume scheme. The MPSA, a generalization of the more commonly used Multi-Point Flux Approximation (MPFA), was discussed in a previous presentation at the 15th USCCN and in reference. To predict the behavior of fibrous and woven architectures, algorithms that compute the local fiber orientation are used. The implementation of the MPSA was verified using analytical solutions, engineering test cases and compared against legacy Finite Element Analysis (FEA) software. The stress analysis models were then applied to real geometries used by NASA in thermal protection systems such as fibrous preforms and woven materials and the results were compared to experimental data.

Federico Semeraro↗