SCIENTIFIC AND TECHNICAL AEROSPACE REPORTS
A Biweekly Publication of the National Aeronautics and Space Administration
VOLUME 44, ISSUE 11 - MAY 30, 2006
90 ASTROPHYSICS
Includes cosmology; celestial mechanics; space plasmas; and interstellar and interplanetary gases and dust.
20060013183 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Heliosheath Space Environment Interactions with Icy Bodies in the Outermost Solar System
Cooper, John F.; Hill, Matthew E.; Richardson, John D.; Sturner, Steven J.; [2006]; 2 pp.; In English; Institute of Geophysics and Planetary Physics, Univ. of California, San Diego, 5th Annual Internation Astrophysics Conference, 3-9 Mar. 2006, Oahu, HI, USA; Copyright; Avail.: CASI: A01, Hardcopy
The Voyager 1 and 2 spacecraft are exploring the space environment of the outermost solar system at the same time that earth-based astronomy continues to discover new icy bodies, one larger than Pluto, in the transitional region outward from the Classical Kuiper Belt to the Inner Oort Cloud. Some of the Scattered Disk Objects in this region periodically pass through the heliosheath, entered by Voyager 1 in Dec. 2004 and later expected to be reached by Voyager 2, and out even beyond the heliopause into the Very Local Interstellar Medium. The less energetic heliosheath ions, important for implantation and sputtering processes, are abundant near and beyond the termination shock inner boundary, but the source region of the more penetrating anomalous cosmic ray component has not yet been found. Advantageous for modeling of icy body interactions, the measured heliosheath flux spectra are relatively more stable within this new regime of isotropic compressional magnetic turbulence than in the upstream heliospheric environment. The deepest interactions and resultant radiation-induced chemistry arise from the inwardly diffusing component of the galactic cosmic ray ions with significant intensity modulation also arising in the heliosheath beyond Voyager 1. Surface gardening by high-velocity impacts of smaller bodies (e.g., fragments of previous KBO collisions) and dust is a further space weathering process setting the time scales for long term exposure of different regolith layers to the ion irradiation. Sputtering and ionization of impact ejecta grains may provide a substantial feedback of pickup ions for multiple cycles of heliosheath acceleration and icy body interaction. Thus the space weathering interactions are potentially of interest not only for effects on sensible surface composition of the icy bodies but also for evolution of the heliosheath plasma energetic ion, and neutral emission environment. Derived from text
Heliosphere; Voyager 1 Spacecraft; Voyager 2 Spacecraft; Aerospace Environments; Oort Cloud; Isotropic Turbulence; Radiation Chemistry; Kuiper Belt; Galactic Cosmic Rays; Ice; Cosmic Rays; Collisions
20060013206 NASA Goddard Space Flight Center, Greenbelt, MD, USA
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Getting a Kick Out of Numerical Relativity
Baker, John G.; Centrella, Joan; Dale, Choi; Koppitz, Michael; vanMeter, James R.; Miller, M. Coleman; [2005]; 14 pp.; In English; Original contains black and white illustrations Contract(s)/Grant(s): ATP02-0043-0056; Copyright; Avail.: CASI: A03, Hardcopy
Recent developments in numerical relativity have made it possible to follow reliably the coalescence of two black holes from near the innermost stable circular orbit to final ringdown. This opens up a wide variety of exciting astrophysical applications of these simulations. Chief among these is the net kick received when two unequal mass or spinning black holes merge. The magnitude of this kick has bearing on the production and growth of supermassive black holes during the epoch of structure formation; and on the retention of black holes in stellar clusters. Here we report the first accurate numerical calculation of this kick, for two nonspinning black holes in a 1.5:1 mass ratio, which is expected based on analytic considerations to give a significant fraction of the maximum possible recoil. Our estimated kick is 10(exp 5) km/s with an error of less than 10%. This is intermediate between the estimates from two recent post-Newtonian analyses and suggests that at redshifts z greater than or approx. equal to 10, halos with masses less than or approx. equal to 10(exp 9) Solar Mass will have difficulty retaining coalesced black holes after major mergers. Author
Black Holes (Astronomy); Coalescing; Circular Orbits; Astrophysics; Star Clusters
20060013207 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Excising das All: Evolving Maxwell waves beyond Scri
vanMeter, James R.; Fiske, David R.; Misner, Charles W.; [2006]; 11 pp.; In English; Original contains black and white illustrations Contract(s)/Grant(s): NNG06LA42C; ATP02-0043-0056; Copyright; Avail.: CASI: A03, Hardcopy
We study the numerical propagation of waves through future null infinity in a conformally compactified spacetime. We introduce an artificial cosmological constant, which allows us some control over the causal structure near null infinity. We exploit this freedom to ensure that all light cones are tilted outward in a region near null infinity, which allows us to impose excision-style boundary conditions in our finite difference code. In this preliminary study we consider electromagnetic waves propagating in a static, conformally compactified spacetime. Author
Space-Time Functions; Finite Difference Theory; Electromagnetic Radiation; Cosmology; Boundary Conditions
20060013213 NASA Goddard Space Flight Center, Greenbelt, MD, USA
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Sensitivity Analysis Applied to Atomic Data Used for X-ray Spectrum Synthesis
Kallman, Tim; [2006]; 2 pp.; In English; NASA Laboratory Astrophysics Workshop, 13-17 Feb. 2006, Las Vegas, NV, USA; No Copyright; Avail.: Other Sources; Abstract Only
A great deal of work has been devoted to the accumulation of accurate quantities describing atomic processes for use in analysis of astrophysical spectra. But in many situations of interest the interpretation of a quantity which is observed, such as a line flux, depends on the results of a modeling- or spectrum synthesis code. The results of such a code depends in turn on many atomic rates or cross sections, and the sensitivity of the observable quantity on the various rates and cross sections may be non-linear and if so cannot easily be derived analytically. In such cases the most practical approach to understanding the sensitivity of observables to atomic cross sections is to perform numerical experiments, by calculating models with various rates perturbed by random (but known) factors. In addition, it is useful to compare the results of such experiments with some sample observations, in order to focus attention on the rates which are of the greatest relevance to real observations. In this paper I will present some attempts to carry out this program, focussing on two sample datasets taken with the Chandra HETG. I will discuss the sensitivity of synthetic spectra to atomic data affecting ionization balance, temperature, and line opacity or emissivity, and discuss the implications for the ultimate goal of inferring astrophysical parameters. Author
Spectrum Analysis; X Rays; Astrophysics; Atomic Physics; Ionization
20060013220 NASA Goddard Space Flight Center, Greenbelt, MD, USA
SPECS: The Submillimeter Probe of the Evolution of Cosmic Structures
Rinehart, Stephen; January 2006; 1 pp.; In English; Society of Photo-Optical Instrumentation Engineers, 24-31 May 2006, Orlando, FL, USA; No Copyright; Avail.: Other Sources; Abstract Only
The idea for the Submillimeter Probe of the Evolution of Cosmic Structure (SPECS) was investigated through NASA Vision Missions Program. In the course of this study, a compelling need for high spatial-resolution far-infrared/submillimeter observations with high angular resolution (50 milliarcseconds) was identified. In order to achieve these scientific goals, a kilometer-baseline FIR/SMM Michelson stellar interferometer is required, operating in the 40-640 micron range with fully cryogenically cooled optics and photon-limited detectors. There are significant technological challenges to developing this mission, including controllable tethered flight, detector equipment, and large cryogenic mechanisms. We present here a concept for SPECS and discuss some of the relevant technical aspects of the mission. Author
Submillimeter Waves; Michelson Interferometers; NASA Programs; Angular Resolution; Far Infrared Radiation; Infrared Astronomy; Tethering
20060013222 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Fourier resolved spectroscopy of 4U 1543-47 during the 2002 outburst
Reig, P.; Papadakis, I. E.; Shrader, C. R.; Kazanas, D.; [2006]; 19 pp.; In English; Original contains black and white illustrations; Copyright; Avail.: CASI: A03, Hardcopy
We have obtained Fourier-resolved spectra of the black-hole binary 4U 1543-47 in the canonical states (high/soft, very high, intermediate and low/hard) observed in this source during the decay of an outburst that took place in 2002. Our objective is to investigate the variability of the spectral components generally used to describe the energy spectra of black-hole systems, namely a disk component, a power-law component attributed to Comptonization by a hot corona and the contribution of the iron line due to reprocessing of the high energy (E greater than or approx, equal to 7 keV) radiation. We find that i) the disk component is not variable on time scales shorter than approx. 100 seconds, ii) the reprocessing emission as manifest by the variability of the Fe K(alpha) line responds to the primary radiation variations down to time scales of approx. 70 ms in the high and very-high states, but longer than 2 s in the low state, iii) the low-frequency QPOs are associated with variations of the X-ray power law spectral component and not to the disk component and iv) the spectra corresponding to the highest Fourier frequency are the hardest (show the flatter spectra) at a given spectral state. These results questions the models that explain the observed power spectra as due to modulations of the accretion rate only. Author
Black Holes (Astronomy); Variability; Energy Spectra; Compton Effect; Power Spectra; Fourier Analysis; Coronas
20060013223 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Future Gamma-Ray Observations of Pulsars and their Environments
Thompson, David J.; [2006]; 1 pp.; In English; 363rd Heraeus Seminar, 'Neutron Stars and Pulsars about 40 Years after their Discovery, 15-19 May 2006, Bad Honnef, Germany; No Copyright; Avail.: Other Sources; Abstract Only
Pulsars and pulsar wind nebulae seen at gamma-ray energies offer insight into particle acceleration to very high energies. Pulsed emission provides information about the geometry and interaction processes in the magnetospheres of these rotating neutron stars, while the pulsar wind nebulae yield information high-energy particles interacting with their surroundings. During the next decade, a number of new and expanded gamma-ray facilities will become available for pulsar studies, including AGILE and GLAST in space and a number of higher-energy ground-based systems. This review describes the capabilities of such observatories to answer some of the open questions about the highest-energy processes involving neutron stars. Author
Gamma Rays; Pulsars; Nebulae; Energetic Particles; Particle Acceleration
20060013228 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Fast X-ray Oscillations During Magnetar Flares
Strohmayer, T.; [2006]; 1 pp.; In English; APS DAP business meetings, 22-25 Apr. 2006, Dallas, TX, USA; No Copyright; Avail.: Other Sources; Abstract Only
'We report on recent studies of high frequency variability during magnetar giant flares. These oscillations may represent the first observations of global shear oscillations in neutron star crusts, and can provide a new tools to study neutron star structure. Author
X Rays; Oscillations; Magnetars; High Frequencies; Variability
20060013324 Naval Research Lab., Washington, DC, USA
Highlights of NRL's (Naval Research Laboratory's) First 75 Years
Calderwood, T. D.; Oct. 1998; 32 pp.; In English Report No.(s): PB2006-109335; NRL/PU/5250-98-368; No Copyright; Avail.: National Technical Information Service (NTIS)
This document presents brief descriptions of projects and a listing of awards received by NRL employees for their work on these projects. NTIS
Navy; Histories; Awards; Personnel
20060013336 NASA Goddard Space Flight Center, Greenbelt, MD, USA
Comprehensive Analysis of RXTE Data from Cyg X-1. Spectral Index-Quasi-Periodic Oscillation Frequency- Luminosity Correlations
Shaposhnikov, Nickolai; Titarchuk, Lev; [2006]; 43 pp.; In English; Original contains black and white illustrations Contract(s)/Grant(s): NCC5-637; No Copyright; Avail.: CASI: A03, Hardcopy
We present timing and spectral analysis of approx. 2.2 Ms of Rossi X-ray Time Explorer (RXTE) archival data from Cyg X-1. Using the generic Comptonization model we reveal that the spectrum of Cyg X-1 consists of three components: a thermal seed photon spectrum, a Comptonized part of the seed photon spectrum and the iron line.We find a strong correlation between 0.1-20 Hz frequencies of quasiperiodic oscillations (QPOs) and the spectral power-law index. Presence of two spectral phases (states) are clearly seen in the data when the spectral indices saturate at low and high values of QPO frequencies. This saturation effect was discovered earlier in a number of black hole candidate (BHC) sources and now we strongly confirm this phenomenon in Cyg X-1. In the soft state this index- QPO frequency correlation shows a saturation of the photon index Gamma approx. 2.1 at high values of the low frequency upsilon(sub L). The saturation level of Gamma approx. 2.1 is the lowest value found yet in BHCs. The bolometric luminosity does not show clear correlation with the index.We also show that Fe K(sub alpha) emission line strength (equivalent width, EW) correlates with the QPO frequency. EW increases from 200 eV in the low/hard state to 1.5 keV in the high/soft state. The revealed observational correlations allow us to propose a scenario for the spectral transition and iron line formation which occur in BHC sources. We also present the spectral state (the power-law index) evolution for eight years of Cyg X-1 observations by RXTE. Author
X Ray Timing Explorer; Spectrum Analysis; Time Measurement; Cygnus Constellation; Black Holes (Astronomy); High Frequencies; Compton Effect
20060013401 NASA Goddard Space Flight Center, Greenbelt, MD, USA
The Supercritical Pile Model for GRBs
Kazanas, D.; Dec. 19, 2005; 39 pp.; In English; Original contains black and white illustrations Report No.(s): astro-ph/0512447-v1; Copyright; Avail.: CASI: A03, Hardcopy
We present the spectral and temporal radiative signatures expected within the 'Supercritical Pile' model of Gamma Ray Bursts (GRB). This model is motivated by the need for a process that provides the dissipation necessary in GRB and presents a well defined scheme for converting the energy stored in the relativistic protons of the Relativistic Blast Waves (RBW) associated with GRB into radiation; at the same time it leads to spectra which exhibit a peak in the burst nuF(sub nu) distribution at an energy E(sub p) approx. equal to 1 MeV in the observer s frame, in agreement with observation and largely independent of the Lorentz factor r of the associated relativistic outflow. Futhermore, this scheme does not require (but does not preclude) acceleration of particles at the shock other than that provided by the isotropization of the flow bulk kinetic energy on the RBW frame. In the present paper we model in detail the evolution of protons, electrons and photons from a RBW to produce detailed spectra of the prompt GRB phase as a function of time from across a very broad range spanning roughly 4 log10Gamma decades in frequency. The model spectra are in general agreement with observations and provide a means for the delineating of the model parameters through direct comparison with trends observed in GRB properties. Author
Gamma Ray Bursts; Time Dependence; Frequencies; Signatures; Photons; Protons; Electrons
Source: NASA
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