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NASA NTRS2005

Chandra Observations of Comet 2P/Encke 2003: First Detection of a Collisionally Thin, Fast Solar Wind Charge Exchange System

We report the results of 15 hr of Chandra observations of comet 2P/Encke 2003 on November 24. X-ray emission from comet Encke was resolved on scales of 500-40,000 km, with unusual morphology due to the presence of a low-density, collisionally thin (to charge exchange) coma. A light curve with peak-to-peak amplitude of 20% consistent with a nucleus rotational period of 11.1 hr was found, further evidence for a collisionally thin coma. We confirm emission lines due to oxygen and neon in the 800-1000 eV range but find very unusual oxygen and carbon line ratios in the 200-700 eV range, evidence for low-density, high effective temperature solar wind composition. We compare the X-ray spectral observation results to contemporaneous measurements of the coma and solar wind made by other means and find good evidence for the dominance of a postshock bubble of expanding solar wind plasma, moving at 600 km/s with charge state composition between that of the "fast" and "slow" solar winds.

Lisse, C. M.↗

NASA NTRS1975

Pioneer 10 observations of the Jovian magnetosphere - Plasma electron results

Examination of electron spectra obtained during inbound transversal of the outer Jovian magnetosphere shows a consistent peak near 4 eV where the thermal component of magnetospheric electrons is observed, corresponding to a temperature of about 50,000 K. The existence of a high beta plasma is inferred on the basis of electron and magnetic field measurements, assuming equilibrium between ions and electrons and pressure balance across the magnetophase. Observations imply the existence of thermal plasma in the outer magnetosphere which may be responsible for large-scale inflation of the outer magnetic field. It is concluded that ambient thermal plasma and photoelectrons in the outer magnetosphere will likely prevent charge buildup in spacecraft, but that it remains a possibility in the inner magnetosphere, where thermal electron measurements are obscured by high background.

Intriligator, D. S.↗

NASA NTRS1975

Pioneer 10 observations of the solar wind and its interaction with Jupiter - Plasma electron results

Typical plasma electron spectra obtained during transversal of the Jovian magnetosheath are discussed. Data from the outer magnetosphere show an enhanced energy tail between approximately 50 eV and 200 eV, indicating heating of the solar wind electrons across the Jovian bow shock. Transversal of the inner magnetosphere produced data implying even higher electron temperatures. Results are consistent with ion observations of a high Mach number bow shock and magnetosheath flow field. They are consistent with a contraction of the Jovian magnetosphere resulting from an increase in the solar wind dynamic pressure similar to, but on a larger scale than that observed in the case of the earth's bow shock.

Intriligator, D. S.↗

NASA NTRS1983

Ring and plasma - The enigmae of Enceladus

The E ring associated with the Kronian moon Enceladus has a lifetime of only a few thousand years against sputtering by slow corotating O ions. The existence of the ring implies the necessity for a continuous supply of matter. Possible particle source mechanisms on Enceladus include meteoroidal impact ejection and geysering. Estimates of ejection rates of particulate debris following small meteoroid impact are on the order of 3 x 10 to the -18th g/(sq cm sec), more than an order of magnitude too small to sustain the ring. A geyser source would need to generate a droplet supply at a rate of approximately 10 to the -16th g/(sq cm sec) in order to account for a stable ring. Enceladus and the ring particles also directly supply both plasma and vapor to space via sputtering. The absence of a 60 eV plasma at the Voyager 2 Enceladus L-shell crossing, such as might have been expected from sputtering, cannot be explained by absorption and moderation of plasma ions by ring particles, because the ring is too diffuse. Evidently, the effective sputtering yield in the vicinity of Enceladus is on the order of, or smaller than, 0.4, about an order of magnitude less than te calculated value. Small scale surface roughness may account for some of this discrepancy.

Haff, P. K.↗

NASA NTRS2006

Precision Fe K-Alpha and Fe K-Beta Line Spectroscopy of the Seyfert 1.9 Galaxy NGC 2992 with Suzaku

We present detailed time-averaged X-ray spectroscopy in the 0.5-10 keV band of the Seyfert 1.9 galaxy NGC 2992 with the Suzaku X-ray Imaging Spectrometers (XIS). The source had a factor approximately 3 higher 2-10 keV flux (approximately 1.2 x l0(exp -11) erg per square cm per s) than the historical minimum and a factor approximately 7 less than the historical maximum. The XIS spectrum of NGC 2992 can be described by several components. There is a primary continuum, modeled as a power-law with a photon index of Gamma = 1.57(sup +0.06) (sup -0.03) that is obscured by a Compton-thin absorber with a column density of 8.01(sup +0.6) (sup -0.5)x l0 (exp 21) per square cm. . There is another, weaker, unabsorbed power-law component (modeled with the same slope as the primary), that is likely to be due to the primary continuum being electron-scattered into our line-of-sight by a region extended on a scale of hundreds of parsecs. We measure the Thomson depth of the scattering zone to be Tau = 0.072 +/- 0.021. An optically-thin thermal continuum emission component, which probably originates in the same extended region, is included in the model and yields a temperature and luminosity of KT = 0.656(sup +0.088) (sup -0.0.61) keV and approximately 1.2 +/- 0.4 x l0 (exp 40) erg per s respectively. We detect an Fe K emission complex which we model with broad and narrow lines and we show that the intensities of the two components are decoupled at a confidence level > 3 sigma. The broad Fe K alpha line has an equivalent width of 118(sup +32) (sup -61) eV and could originate in an accretion disk (with inclination angle greater than approximately 30 deg) around the putative central black hole. The narrow Fe K alpha line has an equivalent width of 1632(sup +47) (sup -26) eV and is unresolved (FWHM < 4630 km per s) and likely originates in distant matter. The absolute flux in the narrow line implies that the column density out of the line-of-sight could be much higher than measured in the line-of-sight, and that the mean (historically-averaged) continuum luminosity responsible for forming the line could be a factor of several higher than that measured from the data. We also detect the Fe K Beta line (corresponding to the narrow Fe K alpha line) with a high signal-to-noise ratio and describe a new robust method to constrain the ionization state of Fe responsible for the Fe K alpha and Fe K Beta lines that does not require any knowledge of possible gravitational and Doppler energy shifts affecting the line energies. For the distant line-emitting matter (e. g. the putative obscuring torus) we deduce that the predominant ionization state is lower than Fe VIII (at 99% confidence), conservatively taking into account residual calibration uncertainties in the XIS energy scale and theoretical and experimental uncertainties in the Fe K fluorescent line energies. From the limits on a possible Compton-reflection continuum it is likely that the narrow Fe K alpha and Fe K Beta lines originate in a Compton-thin structure.

Yaqoob, Tahir↗

NASA NTRS2008

Array-scale performance of TES X-ray Calorimeters Suitable for Constellation-X

Having developed a transition-edge-sensor (TES) calorimeter design that enables high spectral resolution in high fill-factor arrays, we now present array-scale results from 32-pixel arrays of identical closely packed TES pixels. Each pixel in such an array contains a Mo/Au bilayer with a transition temperature of 0.1 K and an electroplated Au or Au/Bi xray absorber. The pixels in an array have highly uniform physical characteristics and performance. The arrays are easy to operate due to the range of bias voltages and heatsink temperatures over which solution better than 3 eV at 6 keV can be obtained. Resolution better than 3 eV has also been obtained with 2x8 time-division SQUID multiplexing. We will present the detector characteristics and show spectra acquired through the read-out chain from the multiplexer electronics through the demultiplexer software to real-time signal processing. We are working towards demonstrating this performance over the range of count rates expected in the observing program of the Constellation-X observatory. We mill discuss the impact of increased counting rate on spectral resolution, including the effects of crosstalk and optimal-filtering dead time.

Kilbourne, C. A.↗

NASA NTRS1989

Kilometric radiation power flux dependence on area of discrete aurora

Kilometer wavelength radiation, measured from distant positions over the North Pole and over the Earth's equator, was compared to the area of discrete aurora imaged by several low-altitude spacecraft. Through correlative studies of auroral kilometric radiation (AKR) with about two thousand auroral images, a stereoscopic view of the average auroral acceleration region was obtained. A major result is that the total AKR power increases as the area of the discrete auroral oval increases. The implications are that the regions of parallel potentials or the auroral plasma cavities, in which AKR is generated, must possess the following attributes: (1) they are shallow in altitude and their radial position depends on wavelength, (2) they thread flux tubes of small cross section, (3) the generation mechanism in them reaches a saturation limit rapidly, and (4) their distribution over the discrete auroral oval is nearly uniform. The above statistical results are true for large samples collected over a long period of time (about six months). In the short term, AKR frequently exhibits temporal variations with scales as short as three minutes (the resolution of the averaged data used). These fluctuations are explainable by rapid quenchings as well as fast starts of the electron cyclotron maser mechanism. There were times when AKR was present at substantial power levels while optical emissions were below instrument thresholds. A recent theoretical result may account for this set of observations by predicting that suprathermal electrons, of energies as low as several hundred eV, can generate second harmonic AKR. The indirect observations of second harmonic AKR require that these electrons have mirror points high above the atmosphere so as to minimize auroral light emissions. The results provide evidence supporting the electron cyclotron maser mechanism.

Saflekos, N. A.↗

NASA NTRS2013

Radial Profiles of the Plasma Electron Characteristics in a 30 kW Arc Jet

The present effort aims to strengthen modeling work conducted at the NASA Ames Research Center by measuring the critical plasma electron characteristics within and slightly outside of an arc jet plasma column. These characteristics are intended to give physical insights while assisting in the formulation of boundary conditions to validate full scale simulations. Single and triple Langmuir probes have been used to achieve estimates of the electron temperature (T(sub e)), electron number density (n(sub e)) and plasma potential (outside of the plasma column) as probing location is varied radially from the flow centerline. Both the electron temperature and electron number density measurements show a large dependence on radial distance from the plasma column centerline with T(sub e) approx. = (3 - 12 eV and n(sub e) approx. = 10(exp 12) - 10(exp 14)/cu cm.

Codron, Douglas A.↗

NASA NTRS2016

Magnetic Reconnection and Modification of the Hall Physics Due to Cold Ions at the Magnetopause

Observations by the four Magnetospheric Multiscale spacecraft are used to investigate the Hall physics of a magnetopause magnetic reconnection separatrix layer. Inside this layer of currents and strong normal electric fields, cold (eV) ions of ionospheric origin can remain frozen-in together with the electrons. The cold ions reduce the Hall current. Using a generalized Ohms law, the electric field is balanced by the sum of the terms corresponding to the Hall current, the v x B drifting cold ions, and the divergence of the electron pressure tensor. A mixture of hot and cold ions is common at the subsolar magnetopause. A mixture of length scales caused by a mixture of ion temperatures has significant effects on the Hall physics of magnetic reconnection.

Andre, M.↗

NASA NTRS1978

X-ray observations of a flare in NGC 4151 from OSO 8

The 2-60-keV flux from NGC 4151 has been observed to change by a factor of 2 on a time scale of 1.5 days. No fluctuations in excess of a factor of 3 are detected on time scales less than 4 hours. During a total observation of approximately 11 days there were no statistically significant changes in spectral shape. The spectrum can be fitted by a power law with photon index of about 1.42 + or - 0.06 and a hydrogen column density of approximately 7.5 + or - 0.5 x 10 to the 22nd power atoms/sq cm. A 2-sigma residual to this fit implies fluorescent Fe line emission with an equivalent width of about 240 eV. Both synchrotron self-Compton and thermal Compton models are consistent with the X-ray data.

Mushotzky, R. F.↗

NASA NTRS1994

Stationary Plasma Thruster Plume Emissions

The emission spectrum from a xenon plasma produced by a Stationary Plasma Thruster provided by the Ballistic Missile Defense Organization (BMDO) was measured. Approximately 270 individual Xe I, Xe II, and XE III transitions were identified. A total of 250 mW of radiated optical emission was estimated from measurements taken at the thruster exit plane. There was no evidence of erosion products in the emission signature. Ingestion and ionization of background gas at elevated background pressure was detected. The distribution of excited states could be described by temperatures ranging from fractions of 1 eV to 4 eV with a high degree of uncertainty due to the nonequilibrium nature of this plasma. The plasma was over 95 percent ionized at the thruster exit plane. Between 10 and 20 percent of the ions were doubly charged. Two modes of operation were identified. The intensity of plasma emission increased by a factor of two during operation in an oscillatory mode. The transfer between the two modes of operation was likely related to unidentified phenomena occurring on a time scale of minutes.

Manzella, David H.↗

NASA NTRS1987

Core plasma in the magnetosphere

The paper presents a review of new findings related to core plasma (which includes ions and electrons with energies less than 50 eV) identified in studies of magnetosphere during 1983-1986. These findings include the cleft ion fountain; the plasmaspheric heavy ion torus; core molecular ions; high core-plasma densities in the plasma-sheet boundary layer; intense transverse heating of core plasmas in the equatorial regions; the supersonic polar wind (H/+/ and He/+/); toroidal or ring heavy-ion distribution functions in the auroral region; conic-to-field-aligned ion signatures of inverted-V auroral events; and the large-scale electron density structure of the magnetosphere. The progress made on modeling core plasma includes simulation of thermal helium heating at the equator; kinetic models of the plasma transport from localized ionospheric regions; time-dependent hydrodynamic models of the polar wind and plasmasphere-ionosphere coupling; and kinetic models of plasmasphere refilling.

Horwitz, J. L.↗

NASA NTRS1992

Can neutrino decay-driven mock gravity save hot dark matter?

The radiative decay of a 30 eV neutrino with a lifetime of order 10 exp 23-24 s has recently been shown to yield a satisfactory explanation of a wide range of problems in astrophysics. In this paper, it is investigated whether the photon flux generated by the radiative decay of a massive neutrino is capable of generating sufficient radiation pressure to cause a 'mock gravitational' collapse of primordial hydrogen clouds. It is shown that when using neutral hydrogen as a source of opacity for mock gravity the time scale for mock gravitational collapse is significantly larger than the expansion time scale. Thus, the model fails as a source of galactic seed perturbations. Furthermore, it is argued that nonlinear feedback mechanisms will be unable to increase the collapse rate of the cloud under mock gravity.

Splinter, Randall J.↗

NASA NTRS2015

Airborne Measurements in Support of the NASA Atmospheric Carbon and Transport - America (ACT-America) Mission

NASA announced the research opportunity Earth Venture Suborbital -2 (EVS-2) mission in support of the NASA's science strategic goals and objectives in 2013. Penn State University, NASA Langley Research Center (LaRC), and other academic institutions, government agencies, and industrial companies together formulated and proposed the Atmospheric Carbon and Transport -America (ACT -America) suborbital mission, which was subsequently selected for implementation. The airborne measurements that are part of ACT-America will provide a unique set of remote and in-situ measurements of CO2 over North America at spatial and temporal scales not previously available to the science community and this will greatly enhance our understanding of the carbon cycle. ACT -America will consist of five airborne campaigns, covering all four seasons, to measure regional atmospheric carbon distributions and to evaluate the accuracy of atmospheric transport models used to assess carbon sinks and sources under fair and stormy weather conditions. This coordinated mission will measure atmospheric carbon in the three most important regions of the continental US carbon balance: Northeast, Midwest, and South. Data will be collected using 2 airborne platforms (NASA Wallops' C-130 and NASA Langley's B-200) with both in-situ and lidar instruments, along with instrumented ground towers and under flights of the Orbiting Carbon Observatory (OCO-2) satellite. This presentation provides an overview of the ACT-America instruments, with particular emphasis on the airborne CO2and backscatter lidars, and the, rationale, approach, and anticipated results from this mission.

Meadows, Byron↗

NASA NTRS1984

Detection of bump-on-tail reduced electron velocity distributions at the electron foreshock boundary

Reduced velocity distributions are derived from three-dimensional measurements of the velocity distribution of electrons in the 7 to 500 eV range in the electron foreshock. Bump-on-tail reduced distributions are presented for the first time at the foreshock boundary consistent with Filbert and Kellogg's proposed time-of-flight mechanism for generating the electron beams. In a significant number of boundary crossings, bump-on-tail reduced distributions were found in consecutive 3 sec measurements made 9 sec apart. It is concluded that, although the beams are linearly unstable to plasma waves according to the Penrose criterion, they persist on a time scale of 3 to 15 sec.

Fitzenreiter, R. J.↗

NASA NTRS1984

Detection of bump-on-tail reduced electron velocity distributions at the electron foreshock boundary

Fitzenreiter, R. J.↗

NASA NTRS2004

Global Geospace Science (GGS)/POLAR Thermal Ion Dynamics Experiments (TIDE) Co-Investigator Program: Mission Operations and Data Analysis (MO/DA)

We have pursued several investigations using the Polar/TIDE data set. The first was a comparison of TIDE high-altitude observations with similar ion flux signatures in the Los Alamos National Laboratory (LANL) magnetospheric plasma analyzer (MPA) data. There are several geosynchronously orbiting satellites with LANL MPA instruments onboard. When the satellite is immersed in fresh plasma sheet electrons, the spacecraft voltage drops to several hundred volts negative, and cold ions are accelerated in to the detector. In the LANL MPA spectrograms, the accelerated cold ions appear as a bright, narrow line, following the voltage of the spacecraft. This "ion line" is seen regularly on the nightside, but has not received much attention. The Polar TIDE observations indicated a ubiquitous "lobal wind" in the near-- magnetotail, a field-aligned stream of approx. 100 eV ions flowing out of both polar ionospheres. The interesting result of this research is that the MPA ion line is also peaked in the field-aligned direction, even though the potential well should be uniform in all directions. It is believed that this is evidence that the lobal winds not only populate the high-latitude lobes, but fill the lobes all the way in to the near-Earth plasma sheet (the location of geosynchronous orbit). This activity developed into a full-scale survey of the lobal wind observations in the TIDE database. The universality of these observations with respect to local time and solar wind conditions implies that the ionospheric outflow is supplying the near-Earth plasma sheet at all times, regardless of magnetic activity. We have conducted a statistical study of the characteristics of the lobal wind in these two data sets FIDE and LANL MPA), finding much similarity between them. Using these characteristics as input conditions to our inner magnetosphere ion transport model, we have conducted simulations of the flow of these particles inside of geosynchronous orbit to show the impact these particles will have on the near-Earth space environment. As the study has progressed, these results have been presented several times to the TIDE team during teleconferences. It is planned to present this survey at the GEM 2004 Summer Workshop, and hopefully at additional conferences in the near future. We are presently writing a paper on the lobal wind occurrence statistics, which should be submitted in April or May to the Journal of Geophysical Research for publication. An undergraduate student at the University of Alabama in Huntsville, Will Maddox, working at NASA MSFC with Dr. Paul Craven, is presently creating a database of the values TIDE moments for the lobal wind (under Dr. Liemohn's guidance), and this will be the focus of a follow-on paper.

Nagy, Andrew↗

NASA NTRS2016

Ground Calibration of the Astro-H (Hitomi) Soft X-Ray Spectrometer

The Astro-H (Hitomi) Soft X-ray Spectrometer (SXS) was a pioneering imaging x-ray spectrometer with 5 eV energy resolution at 6 keV. The instrument used a microcalorimeter array at the focus of a high-throughput soft x-ray telescope to enable high-resolution non-dispersive spectroscopy in the soft x-ray waveband (0.3-12 keV). We present the suite of ground calibration measurements acquired from 2012-2015, including characterization of the detector system, anti-coincidence detector, optical blocking filters, and filter-wheel filters. The calibration of the 36-pixel silicon thermistor microcalorimeter array includes parameterizations of the energy gain scale and line spread function for each event grade over a range of instrument operating conditions, as well as quantum efficiency measurements. The x-ray transmission of the set of five Al/polyimide thin-film optical blocking filters mounted inside the SXS dewar has been modeled based on measurements at synchrotron beamlines, including with high spectral resolution at the C, N, O, and Al K-edges. In addition, we present the x-ray transmission of the dewar gate valve and of the filters mounted on the SXS filter wheel (external to the dewar), including beryllium, polyimide, and neutral density filters.

detectors↗