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All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

High-Energy Emission From Millisecond Pulsars

The X-ray and gamma-ray spectrum of rotation-powered millisecond pulsars is investigated in a model for acceleration and pair cascades on open field lines above the polar caps. Although these pulsars have low surface magnetic fields, their short periods allow them to have large magnetospheric potential drops, but the majority do not produce sufficient pairs to completely screen the accelerating electric field. In these sources, the primary and secondary electrons continue to accelerate to high altitude and their Lorentz factors are limited by curvature and synchrotron radiation reaction. The accelerating particles maintain high Lorentz factors and undergo cyclotron resonant absorption of radio emission, that produces and maintains a large pitch angle, resulting in a strong synchrotron component. The resulting spectra consist of several distinct components: curvature radiation from primary electrons dominating from 1 - 100 GeV, synchrotron radiation from primary and secondary electrons dominating up to about 100 MeV, and much weaker inverse-Compton radiation from primary electrons a t 0.1 - 1 TeV. We find that the relative size of these components depends on pulsar period, period derivative, and neutron star mass and radius with the level of the synchrotron component also depending sensitively on the radio emission properties. This model is successful in describing the observed X-ray and gamma-ray spectrum of PSR J0218+4232 as synchrotron radiation, peaking around 100 MeV and extending up to a turnover around several GeV. The predicted curvature radiation components from a number of millisecond pulsars, as well as the collective emission from the millisecond pulsars in globular clusters, should be detectable with AGILE and GLAST. We also discuss a hidden population of X-ray-quiet and radio-quiet millisecond pulsars which have evolved below the pair death line, some of which may be detectable by telescopes sensitive above 1 GeV. Subject headings: pulsars: general - radiation mechanisms: nonthermal - stars: neutron - gamma rays: theory

Harding, Alice K.↗
NASA NTRS1993

Helium destruction and gamma-ray line emission in accreting neutron stars

The prevalent gamma-ray production channel of a neutron star - emission of 2.2-MeV photons from neutron-proton recombination - is reconsidered. The 2.2-MeV gamma-ray line flux and Compton-scattered continuum are calculated. The flux of gravitationally redshifted 2.2-MeV photons from the brightest accreting X-ray source Scorpius X-1 is about 10 exp -6 gamma/sq cm s, a factor of 20 below the sensitivities on the Compton Gamma-Ray Observatory. The destruction of accreted He-4 leads to significant abundances of lighter elements (D, H-3, He-3) in the upper atmosphere, which are determined. The destroyed He-4 is reformed through fusion reactions a few scale heights beneath the photosphere, and thus does not hamper H-ray bursts.

Bildsten, Lars↗
NASA NTRS2004

Analysis of CRRES PHA Data for Low-Energy-Deposition Events

This effort analyzed the low-energy deposition Pulse Height Analyzer (PHA) data from the Combined Release and Radiation Effects Satellite (CRRES). The high-energy deposition data had been previously analyzed and shown to be in agreement with spallation reactions predicted by the Clemson University Proton Interactions in Devices (CUPID) simulation model and existing environmental and orbit positioning models (AP-8 with USAF B-L coordinates). The scope of this project was to develop and improve the CUPID model by increasing its range to lower incident particle energies, and to expand the modeling to include contributions from elastic interactions. Before making changes, it was necessary to identify experimental data suitable for benchmarking the codes; then, the models to the CRRES PHA data could be applied. It was also planned to test the model against available low-energy proton or neutron SEU data obtained with mono-energetic beams.

McNulty, P. J.↗
NASA NTRS1983

Solar gamma-ray lines

The gamma-ray spectrometer on the Solar Maximum Mission satellite has observed emissions produced by nuclear reactions in over 20 separate solar flares. The observed intensity from different flares ranges over a factor of 100, and the time scale for their production ranges from 10-s pulses to complete events lasting over 1000 s. The emissions include narrow and broadened prompt gamma-ray lines from numerous isotopes from Li-7 to Fe-56 and cover the energy range from 0.431 MeV (Be-7) to 7.12 MeV (O-16). The instrument has also observed emissions at energies greater than 10 MeV from the decay of pi0 mesons, from electron bremsstrahlung, and from the direct observation of greater-than-100-MeV solar neutrons. The intensity, temporal and spectral properties of these emissions are reviewed from the point of view that solar flares represent an astrophysical particle-acceleration site.

Forrest, D. J.↗
NASA NTRS1992

The conductive propagation of nuclear flames. I - Degenerate C + O and O + Ne + Mg white dwarfs

The paper determines the physical properties - speed, width, and density structure - of conductive burning fronts in degenerate carbon-oxygen (C + O) and oxygen-neon-magnesium (O + Ne + Mg) compositions for a grid of initial densities and compositions. The dependence of the physical properties of the flame on the assumed values of nuclear reaction rates, the nuclear reaction network employed, the thermal conductivity, and the choice of coordinate system are investigated. The occurrence of accretion-induced collapse of a white dwarf is found to be critically dependent on the velocity of the nuclear conductive burning front and the growth rate of hydrodynamic instabilities. Treating the expanding area of the turbulent burning region as a fractal whose tile size is identical to the minimum unstable Rayleigh-Taylor wavelength, it is found, for all reasonable values of the fractal dimension, that for initial C + O or O + Ne + Mg densities above about 9 x 10 exp 9 g/cu cm the white dwarf should collapse to a neutron star.

Timmes, F. X.↗
NASA NTRS1993

Transport methods and interactions for space radiations

This report presents a brief history leading to the involvement of the Langley Research Center of the National Aeronautics and Space Administration (NASA) in space-radiation physics and protection. Indeed, a relatively complete summary of technical capability as of the summer of 1990 is given. The Boltzmann equations for coupled ionic and neutronic fields are presented and inversion techniques for the Boltzmann operator are discussed. Errors generated by the straight ahead approximation are derived and are shown to be negligible for most problems of space-radiation protection. A decoupling of projectile propagation from the target fields greatly simplifies the Boltzmann equations and allows an analytic solution of the target fragment transport. Analytic and numerical methods of solving the projectile transport equations are discussed. The nuclear physics underlying the coefficients in the Boltzmann equation is discussed. A coupled-channel optical model is found as a consequence of the loose binding of nuclear matter and closure of the nuclear states in high-energy reactions. Transport solutions with the developed data base are used with laboratory experiments to validate both the transport code and the data base. Numerical benchmarks and comparison with Monte Carlo calculations are also used for code validation.

Wilson, John W.↗
NASA NTRS1997

Radiation Transport and Shielding for Space Exploration and High Speed Flight Transportation

Transportation of ions and neutrons in matter is of direct interest in several technologically important and scientific areas, including space radiation, cosmic ray propagation studies in galactic medium, nuclear power plants and radiological effects that impact industrial and public health. For the proper assessment of radiation exposure, both reliable transport codes and accurate data are needed. Nuclear cross section data is one of the essential inputs into the transport codes. In order to obtain an accurate parametrization of cross section data, theoretical input is indispensable especially for processes where there is little or no experimental data available. In this grant period work has been done on the studies of the use of relativistic equations and their one-body limits. The results will be useful in choosing appropriate effective one-body equation for reaction calculations. Work has also been done to improve upon the data base needed for the transport codes used in the studies of radiation transport and shielding for space exploration and high speed flight transportation. A phenomenological model was developed for the total absorption cross sections valid for any system of charged and/or uncharged collision pairs for the entire energy range. The success of the model is gratifying. It is being used by other federal agencies, national labs and universities. A list of publications based on the work during the grant period is given below and copies are enclosed with this report.

Maung, Khin Maung↗
NASA NTRS2023

The Gamma-Ray Pulsar Phenomenology in View of 3D Kinetic Global Magnetosphere Models

We develop kinetic plasma models of pulsar magnetospheres with magnetic-field-line-dependent plasma injection that reveal the importance of various magnetosphere regions in regulating the gamma-ray emission. We set different particle injection rates for the so-called open, closed, and separatrix zones. Moderate particle injection rates in open and closed zones ensure a global field structure close to the force-free one, while the dissipation occurs mainly in and around the equatorial current sheet. The particles injected in the separatrix zone affect the particle populations that enter the equatorial current sheet region and, therefore, the corresponding accelerating electric fields, particle energies, the spectral cutoff energy, and gamma-ray efficiency. The separatrix zone models reproduce the recently discovered fundamental plane of gamma-ray pulsars consistent with curvature radiation emission, the gamma-ray light-curve shapes, and the radio-lag vs. peak-separation correlation reported in the Fermi second pulsar catalog. The model beaming factors indicate that the pulsar total gamma-ray luminosities listed in the Fermi catalogs are overestimations of the actual ones. We find that the radiation reaction limited regime starts ceasing to govern the high-energy emission for spin-down powers less than 1034 erg/s. Our results also indicate that toward high magnetic inclination angles, the "Y point" around the rotational equator migrates well inside the light cylinder sparking additional peaks in the gamma-ray pulse profiles. We find that an equivalent enhanced particle injection beyond the Y point strengthens these features making the model gamma-ray light curves inconsistent with those observed.

Neutron stars↗
NASA NTRS1997

Csa-19, a radiation-responsive human gene, identified by an unbiased two-gel cDNA library screening method in human cancer cells

A novel polymerase chain reaction (PCR)-based method was used to identify candidate genes whose expression is altered in cancer cells by ionizing radiation. Transcriptional induction of randomly selected genes in control versus irradiated human HL60 cells was compared. Among several complementary DNA (cDNA) clones recovered by this approach, one cDNA clone (CL68-5) was downregulated in X-irradiated HL60 cells but unaffected by 12-O-tetradecanoyl phorbol-13-acetate, forskolin, or cyclosporin-A. DNA sequencing of the CL68-5 cDNA revealed 100% nucleotide sequence homology to the reported human Csa-19 gene. Northern blot analysis of RNA from control and irradiated cells revealed the expression of a single 0.7-kilobase (kb) messenger RNA (mRNA) transcript. This 0.7-kb Csa-19 mRNA transcript was also expressed in a variety of human adult and corresponding fetal normal tissues. Moreover, when the effect of X- or fission neutron-irradiation on Csa-19 mRNA was compared in cultured human cells differing in p53 gene status (p53-/- versus p53+/+), downregulation of Csa-19 by X-rays or fission neutrons was similar in p53-wild type and p53-null cell lines. Our results provide the first known example of a radiation-responsive gene in human cancer cells whose expression is not associated with p53, adenylate cyclase or protein kinase C.

NASA Discipline Radiation Health↗
NASA NTRS2009

Photon Luminescence of the Moon

Luminescence is typically described as light emitted by objects at low temperatures, induced by chemical reactions, electrical energy, atomic interactions, or acoustical and mechanical stress. An example is photoluminescence created when photons (electromagnetic radiation) strike a substance and are absorbed, resulting in the emission of a resonant fluorescent or phosphorescent albedo. In planetary science, there exists X-ray fluorescence induced by sunlight absorbed by a regolith a property used to measure some of the chemical composition of the Moon s surface during the Apollo program. However, there exists an equally important phenomenon in planetary science which will be designated here as photon luminescence. It is not conventional photoluminescence because the incoming radiation that strikes the planetary surface is not photons but rather cosmic rays (CRs). Nevertheless, the result is the same: the generation of a photon albedo. In particular, Galactic CRs (GCRs) and solar energetic particles (SEPs) both induce a photon albedo that radiates from the surface of the Moon. Other particle albedos are generated as well, most of which are hazardous (e.g. neutrons). The photon luminescence or albedo of the lunar surface induced by GCRs and SEPs will be derived here, demonstrating that the Moon literally glows in the dark (when there is no sunlight or Earthshine). This extends earlier work on the same subject [1-4]. A side-by-side comparison of these two albedos and related mitigation measures will also be discussed.

Wilson, T.L.↗
NASA NTRS1997

Gamma-Ray Bursts and Relativistic MHD around Coalescing Neutron Stars

In this proposal we performed the first relativistic hydrodynamic simulations of the binary neutron stars near coalescence. Calculations were performed in three spatial dimensions and were supplemented with magnetohydrodynamic simulations of the magnetic reconnection as the neutron star fluid responds to the relativistic forces of the binary. The ultimate goal of the proposed work was to develop a theoretical model for the temporal and spectral evolution of cosmological gamma-ray bursts produced during the magnetic reconnection. This is the first time such hydrodynamic calculations were performed and some surprising results were obtained. The neutrons stars were observed to compress and heat in the simulations. They could even collapse to black holes many orbits before coalescence. The question then arose as to whether this strange phenomenon could power a gamma-ray burst. The bulk of computing effort in this proposal was therefore devoted to an analysis of the implications of this possible new gamma-ray burst paradigm. The initial focus of the work performed under this proposal was therefore to utilize (3+1) dimensional and spherical numerical general relativistic hydrodynamics to study the origin, evolution, and parametric sensitivity of the collapse instability. We derived modified conditions of hydrostatic equilibrium for stars in the curved space of quasi-static orbits. We followed the magnetic field evolution for approximately one orbit (10 msec). The magnetic field energy was observed to exponentiate with an e-folding time of about 1 msec. Thus, the field should build up very quickly to a magnitude such that reconnection and back reaction of the fluid inhibits further growth.

Mathews, Grant J.↗
NASA NTRS2017

Thermonuclear Bursts with Short Recurrence Times from Neutron Stars Explained by Opacity-Driven Convection

Thermonuclear flashes of hydrogen and helium accreted onto neutron stars produce the frequently observed Type I X-ray bursts. It is the current paradigm that almost all material burns in a burst, after which it takes hours to accumulate fresh fuel for the next burst. In rare cases, however, bursts are observed with recurrence times as short as minutes. We present the first one-dimensional multi-zone simulations that reproduce this phenomenon. Bursts that ignite in a relatively hot neutron star envelope leave a substantial fraction of the fuel unburned at shallow depths. In the wake of the burst, convective mixing events driven by opacity bring this fuel down to the ignition depth on the observed timescale of minutes. There, unburned hydrogen mixes with the metal-rich ashes, igniting to produce a subsequent burst. We find burst pairs and triplets, similar to the observed instances. Our simulations reproduce the observed fraction of bursts with short waiting times of approximately 30%, and demonstrate that short recurrence time bursts are typically less bright and of shorter duration.

nucleosynthesis↗
NASA NTRS2015

A Chandrasekhar Mass Progenitor for the Type Ia Supernova Remnant 3C 397 from the Enhanced Abundances of Nickel and Manganese

Despite decades of intense efforts, many fundamental aspects of Type Ia supernovae (SNe Ia) remain elusive. One of the major open questions is whether the mass of an exploding white dwarf (WD) is close to the Chandrasekhar limit. Here, we report the detection of strong K-shell emission from stable Fe-peak elements in the Suzaku X-ray spectrum of the Type Ia supernova remnant (SNR) 3C 397. The high Ni/Fe and Mn/Fe mass ratios - (0.11-0.24 and 0.018-0.033, respectively) in the hot plasma component that dominates the K-shell emission lines indicate a degree of neutronization in the supernova ejecta that can only be achieved by electron capture in the dense cores of exploding WDs with a near-Chandrasekhar mass. This suggests a single-degenerate origin for 3C 397, since Chandrasekhar mass progenitors are expected naturally if the WD accretes mass slowly from a companion. Together with other results supporting the double-degenerate scenario, our work adds to the mounting evidence that both progenitor channels make a significant contribution to the SN Ia rate in star-forming galaxies.

G41.1-0.3); supernova remnants; nuclear reactions;↗
NASA NTRS2001

Integration of the QMSFRG Database into the HZETRN Code

Accurate nuclear interaction data bases are needed for describing the transport of space radiation in matter including space craft structures, atmospheres, and tissues. Transport models support the identification and development of new material concepts for human and electronic part protection. Quantum effects are manifested in nuclear reactions in several ways including interference effects between terms in the multiple scattering series, the many-body nuclear wave functions (for e.g. the roles of shell structure and Fermi momentum) and nuclear clustering. The quantum multiple scattering fragmentation model (QMSFRG) is a comprehensive model for generating nuclear interaction databases for galactic cosmic ray (GCR) transport. Other nuclear databases including the NUCFRG model and Monte-Carlo simulation codes such as FLUKA, LAHET, HETC, and GEANT ignore quantum effects. These codes fail to describe many important features of nuclear reactions and are thus inaccurate for the evaluation of materials for radiation protection. Previously we have shown that quantum effects are manifested through constructive interference in forward production spectra, the effects of Fermi momentum on production spectra, cluster nuclei knockout, and the nuclear response function. Quantum effects are especially important for heavy ions with mass numbers less than 20 that dominate radiation transport in human tissues and for the materials that are expected to be superior in space radiation protection. We describe the integration of the QMSFRG model into the HZETRN transport code. Integration milestones include proper treatment of odd-even charge-mass effects in nuclear fragmentation and the momentum distribution of nucleon production from GCR primary heavy ions. We have also modified the two-body amplitudes in the model to include nuclear medium effects. In order to include a comprehensive description of the GCR isotopic composition in materials, we have described the isotopic composition of the GCR by extending the 59-isotope version of HZETRN to an 120-isotope version. The isotopic composition of most primary GCR elements (including H, He, C, N, O, Ne, Mg, Si, Ar, Ca, Cr, and Fe) are included in the extended model. We discuss results for the high-energy neutron composition inside materials, and the charge and mass distribution for benchmark GCR problems.

Cucinotta, F. A.↗
NASA NTRS2012

Earth's Most Powerful Natural Particle Accelerator

Thunderstorms launch antimatter, gamma rays, and highly energetic electrons and neutrons to the edge of space. This witches' brew of radiation is generated at the edge of the stratopause, by the strong electric fields associated with lightning discharges. In less than a quarter millisecond, an explosive feedback process takes an initial seed population of electrons, perhaps produced by cosmic rays from dying stars, and amplifies them a billion billion-fold in the rarefied air over high altitude thunderheads. The electrons generate gamma radiation as they travel through the stratosphere and lower mesosphere, momentarily brighter and of harder spectrum than cosmic gamma ray bursts. These electrons ultimately are absorbed by the atmosphere, but the gamma rays continue on, into the upper reaches of the atmosphere, where they in turn generate a new population of electrons, positrons, and energetic neutrons. These secondary electrons and positrons move along the magnetic field, and can reach near-earth space, streaming through the inner radiation belts, and possibly contributing to the trapped populations there. First postulated by Wilson in 1925, and serendipitously discovered by the Compton Gamma Ray Observatory in 1994 [Fishman et al.], these events, known as "Terrestrial Gamma ray Flashes" (TGFs), represent the most intense episodes of particle acceleration on or near the Earth, resulting in electrons with energies up to 100 MeV. Recent observations by the RHESSI [Smith et al., 2004], Fermi [Briggs et al., 2010], and AGILE [Tavani et al., 2011] satellites, and theoretical and computational modeling, have suggested that the relativistic runaway electron avalanche (RREA) mechanism [Gurevich, 1992], and important modifications, such as the relativistic feedback discharge (RFD) model [Dwyer 2012] can best explain the observations at present. In these models, strong thunderstorm electric fields drive seed electrons, generated from cosmic ray interactions, into a runaway discharge, in which the seed electrons continually gain energy from the electric field, creating a host of secondaries as they interact with the background atmospheric gas. The feedback mechanisms include backwards-propagating positrons and gamma rays, which then can generate new "seed" electrons at the base of the acceleration region, and themselves generate further avalanche chain reactions, greatly amplifying the initial seed population. All these processes happen in the stratosphere, in the altitude range near 15-20 km, where the electric fields and mean free paths are appropriate to allow the discharge to develop.

Rowland, Doug↗
NASA NTRS2014

Gamma-Ray Emission in Dissipative Pulsar Magnetospheres: from Theory to Fermi Observations

We compute the patterns of gamma-ray emission due to curvature radiation in dissipative pulsar magnetospheres. Our ultimate goal is to construct macrophysical models that are able to reproduce the observed gamma-ray light curve phenomenology recently published in the Second Fermi Pulsar Catalog. We apply specific forms of Ohm's law on the open field lines using a broad range for the macroscopic conductivity values that result in solutions ranging, from near-vacuum to near-force-free. Using these solutions, we generate model gamma-ray light curves by calculating realistic trajectories and Lorentz factors of radiating particles under the influence of both the accelerating electric fields and curvature radiation reaction. We further constrain our models using the observed dependence of the phase lags between the radio and gamma-ray emission on the gamma-ray peak separation. We perform a statistical comparison of our model radio-lag versus peak-separation diagram and the one obtained for the Fermi standard pulsars. We find that for models of uniform conductivity over the entire open magnetic field line region, agreement with observations favors higher values of this parameter. We find, however, significant improvement in fitting the data with models that employ a hybrid form of conductivity, specifically, infinite conductivity interior to the light cylinder and high but finite conductivity on the outside. In these models the gamma-ray emission is produced in regions near the equatorial current sheet but modulated by the local physical properties. These models have radio lags near the observed values and statistically best reproduce the observed light curve phenomenology. Additionally, they also produce GeV photon cut-off energies.

stars↗
NASA NTRS1999

High-Energy Space Propulsion Based on Magnetized Target Fusion

A conceptual study is made to explore the feasibility of applying magnetized target fusion (MTF) to space propulsion for omniplanetary travel. Plasma-jet driven MTF not only is highly amenable to space propulsion, but also has a number of very attractive features for this application: 1) The pulsed fusion scheme provides in situ a very dense hydrogenous liner capable of moderating the neutrons, converting more than 97% of the neutron energy into charged particle energy of the fusion plasma available for propulsion. 2) The fusion yield per pulse can be maintained at an attractively low level (< 1 GJ) despite a respectable gain in excess of 70. A compact, low-weight engine is the result. An engine with a jet power of 25 GW, a thrust of 66 kN, and a specific impulse of 77,000 s, can be achieved with an overall engine mass of about 41 metric tons, with a specific power density of 605 kW/kg, and a specific thrust density of 1.6 N/kg. The engine is rep-rated at 40 Hz to provide this power and thrust level. At a practical rep-rate limit of 200 Hz, the engine can deliver 128 GW jet power and 340 kN of thrust, at specific power and thrust density of 1,141 kW/kg and 3 N/kg respectively. 3) It is possible to operate the magnetic nozzle as a magnetic flux compression generator in this scheme, while attaining a high nozzle efficiency of 80% in converting the spherically radial momentum of the fusion plasma to an axial impulse. 4) A small fraction of the electrical energy generated from the flux compression is used directly to recharge the capacitor bank and other energy storage equipment, without the use of a highvoltage DC power supply. A separate electrical generator is not necessary. 5) Due to the simplicity of the electrical circuit and the components, involving mainly inductors, capacitors, and plasma guns, which are connected directly to each other without any intermediate equipment, a high rep-rate (with a maximum of 200 Hz) appears practicable. 6) All fusion related components are within the current state of the art for pulsed power technology. Experimental facilities with the required pulsed power capabilities already exist. 7) The scheme does not require prefabricated fuel target and liner hardware in any esoteric form or state. All necessary fuel and liner material are introduced into the engine in the form of ordinary matter in gaseous state at room temperature, greatly simplifying their handling on board. They are delivered into the fusion reaction chamber in a completely standoff manner.

Thio, Y. C. F.↗