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NASA NTRS2004

Future Probes of the Neutron Star Equation of State Using X-ray Bursts

Observations with NASA s Rossi X-ray Timing Explorer (RXTE) have resulted in the discovery of fast (200 - 600 Hz), coherent X-ray intensity oscillations (hereafter, %urstoscillations ) during thermonuclear X-ray bursts from 12 low mass X-ray binaries (LMXBs). Although many of their detailed properties remain to be fully understood, it is now beyond doubt that these oscillations result from spin modulation of the thermonuclear burst flux from the neutron star surface. Among the new timing phenomena revealed by RXTE the burst oscillations are perhaps the best understood, in the sense that many of their properties can be explained in the framework of this relatively simple model. Because of this, detailed modelling of burst oscillations can be an extremely powerful probe of neutron star structure, and thus the equation of state (EOS) of supra-nuclear density matter. Both the compactness parameter beta = GM/c(sup 2)R, and the surface velocity, nu(sub rot) = Omega(sub spin)R, are encoded in the energy-dependent amplitude and shape of the modulation pulses. The new discoveries have spurred much new theoretical work on thermonuclear burning and propagation on neutron stars, so that in the near future it is not unreasonable to think that detailed physical models of the time dependent flux from burning neutron stars will be available for comparison with the observed pulse profiles from a future, large collecting area X-ray timing observatory. In addition, recent high resolution burst spectroscopy with XMM/Newton suggests the presence of redshifted absorption lines from the neutron star surface during bursts. This leads to the possibility of using large area, high spectral resolution measurements of X-ray bursts as a precise probe of neutron star structure. In this work I will explore the precision with which constraints on neutron star structure, and hence the dense matter EOS, can be made with the implementation of such programs.

Strohmayer, Tod E.↗

NASA NTRS1973

Approximations for neutron emission spectra from proton collisions between 20 and 500 MeV on nuclei of A greater than or equal to 12

When high energy protons from solar proton events or trapped radiation belts impinge on spacecraft structures, secondary particles are emitted. The most pernicious secondaries, from either a biological or physical standpoint, are the cascade and evaporation neutrons because of their reaction with matter leading to radioactive materials in the spacecraft structures. Empirically determined cascade and evaporation neutron emission spectra for protons of energy between 20 and 500 MeV incident on all materials at or above carbon in mass number are presented.

Burrell, M. O.↗

NASA NTRS2001

Simultaneous Spectral and Timing Observations of Accreting Neuron Stars

The goal of this proposal was to perform simultaneous x-ray spectral and millisecond timing observations of accreting neutron stars to further our understanding of their accretion dynamics and in the hope of using these systems as probes of the physics of strong gravitational fields. Observations of the neutron star binaries 4U0614+091, 4U1728-34, 4U1820-30, and Cyg X-2 were carried out with RXTE and BeppoSAX, ASCA, and Chandra (not all simultaneously). In addition, archival data were analyzed for 4U0614+091 and 4U1820-30. This investigation led to publication of three papers in peer-reviewed journals. These are listed below. In addition, the results were presented at several meetings including the two poster presentations listed below. Dr. Santina Piraino visited SAO for 4 months during 2000 to collaborate on analysis of the data from NAG5-8408 and NAG5-9104.

Kaaret, P.↗

NASA NTRS1989

The Nuclear Astrophysics Explorer

The Nuclear Astrophysics Explorer was proposed in 1986 for NASA's Explorer Concept Study Program by an international collaboration of 25 scientists from nine institutions. The one-year feasibility study began in June 1988. The Nuclear Astrophysics Explorer would obtain high resolution observations of gamma-ray lines, E/Delta E about 1000, at a sensitivity of about 0.000003 ph/sq cm s, in order to study fundamental problems in astrophysics such as nucleosynthesis, supernovae, neutron star and black-hole physics, and particle acceleration and interactions. The instrument would operate from 15 keV to 10 Mev and use a heavily shielded array of nine cooled Ge spectrometers in a very low background configuration. Its 10 deg FWHM field of view would contain a versatile coded mask system which would provide two-dimensional imaging with 4 deg resolution, one-dimensional imaging with 2 deg resolution, and efficiendt measurements of diffuse emission. An unshielded Ge spectrometer would obtain wide-field measurements of transient gamma-ray sources. The earliest possible mission would begin in 1995.

Matteson, J. L.↗

NASA NTRS1995

Radiation safety aspects of commercial high-speed flight transportation

High-speed commercial flight transportation is being studied for intercontinental operations in the 21st century, the projected operational characteristics for these aircraft are examined, the radiation environment as it is now known is presented, and the relevant health issues are discussed. Based on a critical examination of the data, a number of specific issues need to be addressed to ensure an adequate knowledge of the ionizing radiation health risks of these aircraft operations. Large uncertainties in our knowledge of the physical fields for high-energy neutrons and multiply-charged ion components need to be reduced. Improved methods for estimating risks in prenatal exposure need to be developed. A firm basis for solar flare monitoring and forecasting needs to be developed with means of exposure abatement.

Wilson, John W.↗

NASA NTRS2003

Monte Carlo Methods in Materials Science Based on FLUKA and ROOT

A comprehensive understanding of mitigation measures for space radiation protection necessarily involves the relevant fields of nuclear physics and particle transport modeling. One method of modeling the interaction of radiation traversing matter is Monte Carlo analysis, a subject that has been evolving since the very advent of nuclear reactors and particle accelerators in experimental physics. Countermeasures for radiation protection from neutrons near nuclear reactors, for example, were an early application and Monte Carlo methods were quickly adapted to this general field of investigation. The project discussed here is concerned with taking the latest tools and technology in Monte Carlo analysis and adapting them to space applications such as radiation shielding design for spacecraft, as well as investigating how next-generation Monte Carlos can complement the existing analytical methods currently used by NASA. We have chosen to employ the Monte Carlo program known as FLUKA (A legacy acronym based on the German for FLUctuating KAscade) used to simulate all of the particle transport, and the CERN developed graphical-interface object-oriented analysis software called ROOT. One aspect of space radiation analysis for which the Monte Carlo s are particularly suited is the study of secondary radiation produced as albedoes in the vicinity of the structural geometry involved. This broad goal of simulating space radiation transport through the relevant materials employing the FLUKA code necessarily requires the addition of the capability to simulate all heavy-ion interactions from 10 MeV/A up to the highest conceivable energies. For all energies above 3 GeV/A the Dual Parton Model (DPM) is currently used, although the possible improvement of the DPMJET event generator for energies 3-30 GeV/A is being considered. One of the major tasks still facing us is the provision for heavy ion interactions below 3 GeV/A. The ROOT interface is being developed in conjunction with the CERN ALICE (A Large Ion Collisions Experiment) software team through an adaptation of their existing AliROOT (ALICE Using ROOT) architecture. In order to check our progress against actual data, we have chosen to simulate the ATIC14 (Advanced Thin Ionization Calorimeter) cosmic-ray astrophysics balloon payload as well as neutron fluences in the Mir spacecraft. This paper contains a summary of status of this project, and a roadmap to its successful completion.

Pinsky, Lawrence↗

NASA NTRS2007

Fast X-ray Oscillations during Magnetar Flares

The giant flares produced by highly magnetized neutron stars, "magnetars," are the brightest sources of high energy radiation outside our solar system. Serendipitous observations with NASA's Rossi X-ray Timing Explorer (RXTE) of the two most recent flares resulted in the discovery of high frequency oscillations in their X-ray fluxes. The frequencies of these oscillations range from approx. 20 Hz to as high as 1800 Hz, and may represent the first detection of global oscillation modes of neutron stars. Here I will present an observational and theoretical overview of these oscillations and discuss how they might allow us to probe neutron star interiors and dense matter physics.

Strohmayer, Tod E.↗

NASA NTRS2008

"Magnetar Hyper-Flares: Whole Lotta Shakin' Goin' on"

The giant flares produced by highly magnetized neutron stars, "magnetars," are the brightest sources of high energy radiation outside our solar system. High frequency oscillations have been discovered during portions of the two most recently observed giant flares which may represent the first detection of global oscillation modes of neutron stars. I will give an observational and theoretical overview of these oscillations and describe how they might allow us to probe neutron star interiors and dense matter physics.

Strohmayer, Tod↗

NASA NTRS2009

Fast X-Ray Oscillations during Magnetar Flares

Strohmayer Tod E.↗

NASA NTRS1977

X-ray bursts and neutron-star thermonuclear flashes

A description is presented of a model concerning the production of X-ray bursts by thermonuclear flashes in the freshly accreted matter near the surface of an accreting neutron star. An investigation is conducted regarding the physical processes relevant to such thermonuclear flashes. It is concluded that thermonuclear flashes may account for some, but not all, of the observed X-ray burst sources. Attention is given to a neutron star undergoing accretion of mass from a binary stellar companion, aspects of energetics, nuclear reactions, and heat transport mechanisms.

Joss, P. C.↗

NASA NTRS1977

On the emission of neutrinos and gravitational waves in the formation of neutron stars

The various modes in which the energy generated by the formation of a neutron star or black hole due to collapse of a stellar core can appear are investigated, and physical constraints are placed on this energy distribution by noting that neutron stars appear to have been found in at least six X-ray binaries and one binary pulsar. The energy generated by a supernova during the collapse of a stellar core to a neutron star is considered along with the manner in which this energy is distributed in the different modes. It is shown that the gravitational binding energy of a neutron star is converted mostly into kinetic energy of rotation or is emitted as neutrinos, gravitational waves, or both. The energy release through mass ejection and cosmic rays is suggested to be no more than a few percent of the total energy involved. A possible scenario is outlined for the case where the initial rotation velocity of the collapsing core exceeds some critical limit. It is concluded that gravitational radiation will be the ultimate outlet for most of the binding energy in this case.

Kondo, Y.↗

NASA NTRS1989

X ray timing observations and gravitational physics

Photon-rich x ray observations on bright compact galactic sources will make it possible to detect many fast processes that may occur in these systems on millisecond and submillisecond timescales. Many of these processes are of direct relevance to gravitational physics because they arise in regions of strong gravity near neutron stars and black holes where the dynamical timescales for compact objects of stellar mass are milliseconds. To date, such observations have been limited by the detector area and telemetry rates available. However, instruments such as the proposed X ray Large Array (XLA) would achieve collecting areas of about 100 sq m. This instrument has been described elsewhere (Wood and Michelson 1988) and was the subject of a recent prephase A feasibility study at Marshall Space Flight Center. Observations with an XLA class instrument will directly impact five primary areas of astrophysics research: the attempt to detect gravitational radiation, the study of black holes, the physics of mass accretion onto compact objects, the structure of neutron stars and nuclear matter, and the characterization of dark matter in the universe. Those observations are discussed that are most directly relevant to gravitational physics: the search for millisecond x ray pulsars that are potential sources of continuous gravitational radiation; and the use of x ray timing observations to probe the physical conditions in extreme relativistic regions of space near black holes, both stellar-sized and supermassive.

Michelson, Peter F.↗

NASA NTRS1965

<interdisciplinary space-oriented research program in the physical, life, and engineering sciences< progress report

Physics research - plasmas, gas dynamics, magnetic effects, neutron absorption, shell theory, elasticity, and radial heat

PLASMA↗

NASA NTRS1972

A liquid radiation detector with high spatial resolution

Detector, using point anode, minimizes problem of oblique tracks by permitting construction of very thin counter. Detector is useful in cosmic ray and high energy physics research and X-ray and neutron diffraction technology.

Alvarez, L.↗

NASA NTRS1975

Computers vs. wind tunnels for aerodynamic flow simulations

It is pointed out that in other fields of computational physics, such as ballistics, celestial mechanics, and neutronics, computations have already displaced experiments as the principal means of obtaining dynamic simulations. In the case of aerodynamic investigations, the complexity of the computational work involved in solving the Navier-Stokes equations is the reason that such investigations rely currently mainly on wind-tunnel testing. However, because of inherent limitations of the wind-tunnel approach and economic considerations, it appears that at some time in the future aerodynamic studies will chiefly rely on computational flow data provided by the computer. Taking into account projected development trends, it is estimated that computers with the required capabilities for a solution of the complete viscous, time-dependent Navier-Stokes equations will be available in the mid-1980s.

Chapman, D. R.↗

NASA NTRS2002

Kronos: A Multiwavelength Observatory for Mapping Accretion-Driven Sources

Kronos is a multiwavelength observatory proposed as a NASA Medium Explorer. Kronos is designed to make use of the natural variability of accreting sources to create microarcsecond-resolution maps of the environments of supermassive black holes in active galaxies and stella-size black holes in binary systems and to characterize accretion processes in Galactic compact binaries. Kronos will obtain broad energy range spectroscopic data with co-aligned X-ray, ultraviolet, and optical spectrometers. The high-Earth orbit of Kronos enables well-sampled, high time-resolution observations, critical for the innovative and sophisticated methods that are used to understand the accretion flows, mass outflows, jets, and other phenomena found in accreting sources. By utilizing reverberation mapping analysis techniques, Kronos produces advanced high-resolution maps of unprecedented resolution of the extreme environment in the inner cores of active galaxies. Similarly, Doppler tomography and eclipse mapping techniques characterize and map Galactic binary systems, revealing the details of the physics of accretion processes in black hole, neutron star, and white dwarf binary systems. The Kronos instrument complement, sensitivity, and orbital environment make it suitable to aggressively address time variable phenomena in a wide range of astronomical objects from nearby flare stars to distant galaxies.

Peterson, Bradley M.↗

NASA NTRS2004

Kronos: A Satellite for Astrotomography

Kronos, a Medium Explorer concept, is designed to initiate a new era in astrophysics, fully opening the domain of time by enabling extended simultaneous multiwavelength (X-ray, UV, and optical) spectroscopic monitoring of variable accretion-driven sources. The primary design goal of the mission is to obtain high-fidelity velocity-delay maps of the broad-line region in active galactic nuclei (AGNs) and thus determine the geometry and structure of AGNs on microarcsecond scales. Doppler tomography and eclipse mapping techniques will be used to characterize and map Galactic binary systems, revealing the details of the physics of accretion processes in black hole, neutron star, and white dwarf binary systems. The high-Earth orbit of Kronos enables well-sampled, high time-resolution observations, critical for the innovative and sophisticated methods that are used to understand the accretion flows, mass outflows, jets, and other phenomena found in accreting sources.

Peterson, B. M.↗

NASA NTRS1992

Can accretion onto isolated neutron stars produce gamma-ray bursts?

It is shown here that, if slow accretion onto high-velocity neutron stars from the interstellar medium is to be the origin of gamma-ray bursts, the accretion physics is very different from what applies for local low-velocity neutron stars. For halo neutron stars with high magnetic fields and velocities, electromagnetic dipole radiation pressure prevents accretion unless the period is longer than tens of seconds; the centrifugal barrier will then prevent accretion until the period reaches several thousand seconds. For periods as long as this, accretion may proceed through Kelvin-Helmholtz instability at the magnetopause boundary. At interstellar densities and neutron-star magnetic fields of about 10 exp 12 G, the accretion rate by this process can be much larger than the Bondi-Hoyle accretion rate, but is still well below what is needed for slow-accretion burst models. It is concluded that slow accretion onto high-velocity neutron stars in the halo cannot be the origin of gamma-ray bursts.

Harding, Alice K.↗