Bulletin of the American Physical Society
2008 APS April Meeting and HEDP/HEDLA Meeting
Volume 53, Number 5
Friday–Tuesday, April 11–15, 2008; St. Louis, Missouri
Session L8: Neutron Stars, Pulsars, and Black Holes |
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Sponsoring Units: DAP Chair: Jonathan Arons, University of California, Berkeley Room: Hyatt Regency St. Louis Riverfront (formerly Adam's Mark Hotel), Promenade A |
Sunday, April 13, 2008 1:30PM - 1:42PM |
L8.00001: Nuclear Equation of State of High Density Matter. Jirina Stone The density and temperature dependence of energy per particle of a system (the Equation of State - EOS) is a fundamental ingredient of all models of nuclear matter and stars. As baryons and leptons form the main components of all stars, knowledge of nuclear physics and weak interactions is essential for correct understanding of birth, life and death of stars. We compare results obtained with EOS's based on a selection of well established nucleon-nucleon effective interactions in comparison with new results from the quark-meson coupling model and the ORNL-Oxford effective potential. Properties of of cold non-rotating and rapidly rotating neutron stars, calculated on the basis of the models, are presented and discussed. [Preview Abstract] |
Sunday, April 13, 2008 1:42PM - 1:54PM |
L8.00002: A parametrized equation of state for neutron-star matter John L. Friedman, Jocelyn S. Read, Benjamin D. Lackey, Benjamin Owen Astrophysical constraints on the nuclear equation of state above nuclear density have been studied simply by looking at which members of the set of candidate equations of state are ruled out by observations of neutron stars. A systematic study of observational constraints requires a parameterized equation of state with a set of parameters smaller than the number of neutron star properties that have been measured or will have been measured in the next several years. And the set must be large enough to accurately approximate the large set of candidate EOS's. We find that a parametrized EOS based on piecewise polytropes with 3 free parameters matches to about 5\% rms error the universe of candidate EOSs at densities below the central density of $1.4\, M_\odot$ stars. Adding observations of more massive stars constrains the higher density part of the EOS and requires an additional parameter. [Preview Abstract] |
Sunday, April 13, 2008 1:54PM - 2:06PM |
L8.00003: Astrophysical constraints on the parameter space of the neutron-star equation of state Benjamin Lackey, Jocelyn Read, Benjamin Owen, John Friedman The neutron-star equation of state is largely unknown above nuclear density but can be accurately parameterized by only 4 free parameters. The parameter space may be constrained with observations of neutron stars, and we find the constraint surfaces associated with causality and with observed limits on masses, radii, redshift, moment of inertia, and spin frequency. There are only a few hard (model-independent) constraints; of these, the most stringent is associated with the largest observed neutron-star masses, and this constraint only restricts the parameter space to one side of a constraint surface. Anticipated future observations of moments of inertia of stars with known masses can more sharply constrain the parameter space, confining the parameter space to a surface. [Preview Abstract] |
Sunday, April 13, 2008 2:06PM - 2:18PM |
L8.00004: Spin Frequencies and Magnetic Fields of Neutron Stars: Implications of the kHz QPOs Recently Discovered in Circinus X-1 Stratos Boutloukos, Frederick Lamb The paired kilohertz quasi-periodic oscillations (kHz QPOs) recently discovered in the X-ray emission of Cir X-1 are generally similar to those seen in disk-accreting neutron stars with relatively weak magnetic fields, establishing that the compact object in the Cir X-1 system is such a star. Periodic oscillations have not yet been detected from Cir X-1, so its spin rate has not yet been measured directly. In many stars that produce kHz QPOs, the frequency separation $\Delta\nu$ of the QPO pair is equal or roughly equal to the stellar spin rate $\nu_s$ or to $\nu_s$/2. The involvement of the stellar spin in producing $\Delta\nu$ indicates that the magnetic fields of these stars are dynamically important. If the mechanism that produces the kilohertz QPOs is similar in all stars, the value of $\Delta\nu$ provides a rough estimate of the star's spin rate. In Cir X-1, $\Delta\nu$ varies by 167 Hz, from $\sim$230 Hz to $\sim$500 Hz, the largest variation seen so far in any neutron star. The frequency $\nu_u$ of the upper kHz QPO in Cir X-1 is up to a factor of three smaller than is typical. The low observed values of $\nu_u$ and the large variation of $\Delta\nu$ challenge current models for the generation of kHz QPOs. We discuss the implications of the observed properties of the Cir X-1 kHz QPOs for mechanisms for generating the kHz QPOs in Cir X-1 and other accreting neutron stars. This research was supported in part by NASA grant NAG 5-12030, NSF grant AST 0709015, and funds of the Fortner Endowed Chair at Illinois. [Preview Abstract] |
Sunday, April 13, 2008 2:18PM - 2:30PM |
L8.00005: A Model of Waveform Variations and Intermittency in Accretion-Powered Millisecond Pulsars Frederick K. Lamb, Stratos Boutloukos, Alexander Clare, Daniel Dorris, Sandor Van Wassenhove, Wenfei Yu, Coleman Miller We suggest that the accretion-powered X-ray oscillations of most accreting millisecond pulsars (MSPs) are weak and nearly sinusoidal because they are aligned or nearly aligned rotators. The properties of the emitting region on the neutron star surface are determined by the geometry and strength of the star's magnetic field and where accreting plasma enters the magnetosphere. They are therefore expected to change with time as the character of the flow in the inner disk changes. X-ray emission and general relativistic ray-tracing computations show that if accretion-powered MSPs are nearly aligned, modest changes in the size and shape of the emitting region can explain the pulse waveform variations and large changes in apparent spin-frequency observed in many of them and the sudden appearance and disappearance of pulsations (intermittency) observed in some. This model can also explain why accretion-powered periodic oscillations have not been detected from many neutron stars in low-mass X-ray binary systems. [Preview Abstract] |
Sunday, April 13, 2008 2:30PM - 2:42PM |
L8.00006: Pulsar kicks with electrons in Landau levels and active, sterile neutrinos Leonard Kisslinger Very large velocities of pulsars have been observed: called pulsar kicks. The electrons produced with the anti-neutrinos during the first about 50 seconds of the supernova event are in Landau levels due to the strong magnetic field. This leads to asymmetry in the neutrino momentum. We derive the momentum given the proto-neutron star during the time when the neutrino sphere is near the surface of the proto-neutron star and find that highly luminescent neutron stars could receive a velocity of more than 1000 km/s, as has been observed[1]. During the first 10 seconds, when most of the energy emitted by neutrinos occurs, only neutrinos at the edge of the neutrino sphere are emitted, and little asymmetric momentum is produced unless the neutrinos oscillate to sterile neutrinos. We use a model with two sterile neutrinos obtained by fits to the MiniBoone and LSND experiments, and show that large pulsar kicks can be obtained [2] \newline [1] E.M. Henley, M.B. Johnson, L.S. Kisslinger, astro-ph/0706.1511 \newline [2] L.S Kisslinger, E.M. Henley, M.B Johnson, astro-ph/0712.0197 [Preview Abstract] |
Sunday, April 13, 2008 2:42PM - 2:54PM |
L8.00007: Particle energization and radiation in magnetized black hole accretion Edison Liang, Guy Hilburn, Siming Liu, Hui Li, Charles Gammie We study nonthermal electron heating by MHD turbulence generated by the magneto-rotational instability in magnetized accretion flows onto black holes. Using a combination of relativistic MHD, Fokker-Planck and Monte Carlo simulations, we study the spectral and temporal properties of the radiation output, and their dependence on the disk input parameters. Of particular interest are the roles of the magnetic field and density of the initial plasma. [Preview Abstract] |
Sunday, April 13, 2008 2:54PM - 3:06PM |
L8.00008: Testing the general relativistic ``no-hair'' theorems using the galactic center black hole SgrA* Clifford M. Will If a class of stars orbits the central black hole in our galaxy in short period ($\sim 0.1$ year), high eccentricity ($\sim 0.9$) orbits, they will experience precessions of their orbital planes induced by both relativistic frame-dragging and the quadrupolar gravity of the hole, at levels that could be as large as 10 $\mu$arcseconds per year, if the black hole is rotating faster than 1/2 of its maximum rotation rate. Astrometric observations of the orbits of at least two such stars can in principle lead to a determination of the angular momentum vector ${\bf J}$ of the black hole and its quadrupole moment $Q_2$. This could lead to a test of the general relativistic no-hair theorems, which demand that $Q_2 = - J^2/M$. Future high-precision adaptive infrared optics instruments may make such a fundamental test of the black-hole paradigm possible. [Preview Abstract] |
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