1 / 54

Double feature:

Dive into theories of fast oscillations during magnetar giant flares and measuring gravitational waves using Pulsar Timing Arrays. Understand neutron star dynamics, Alfven waves, and QPOs in this fascinating exploration of astrophysical phenomena.

teresajennings
Télécharger la présentation

Double feature:

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Double feature: Yuri Levin, Leiden 1. The theory of fast oscillations during magnetar giant flares 2. Measuring gravitational waves using Pulsar Timing Arrays

  2. Part 1. NEUTRON STARS: B crust core: n (superfluid) p (supercond.) e 20 km • spin=0.01-716 Hz km

  3. Physics preliminaries: magnetic fields in non-resistive media Field lines: 1. Are frozen into the medium 2. Possess tension and pressure ~B B 2 Alfven waves!

  4. 15 Magnetars: ultra-magnetic neutron stars. B~10 Gauss Duncan & Thompson 92 Usov 94 Thompson et al 94-06 crust • Slowly rotating, with • X-ray emission powered by • magnetic energy • Some magnetars also release flares 3 Giant flares: 1979, 1998, 2004 Mazetz, Hurley, etc.

  5. Discovery of Quasi-Periodic Oscillations (Israel et al 2005)

  6. Strohmayer & Watts 06

  7. Israel et al 05 Barat et al 83 Watts & Strohmayer 06 Strohmayer & Watts 06 Oscilations at several frequencies: 18, 30, 40, 90, 625, etc., Hz. Interpretation 0:torsional vibration of the neutron star crust (starquake!) Duncan, et al 98-06 • 18 Hz does not work • QPOs highly intermittent • Physics does not work Three caveats: Key issue: high B-field

  8. Torsional vibration of the whole star L. 06, L. 07, MNRAS also Glampedakis et 06 • Magnetically coupling to the core on 0.01-0.1 second timescale. • Pure crustal modes don’t exist. • Alfven continuum in the core. Initial crustal modes decay in <second What happens then? crust • Normal-mode analysis: • global torsional mode most likely • doesn’t exist

  9. Crust-core dynamics: • Magnetically coupling to the core on 0.01-0.1 second timescale. • Pure crustal modes don’t exist. • Alfven continuum in the core. Initial crustal displacements decay in <second What happens then? crust • Normal-mode analysis: • global torsional mode likely don’t • exist • Resonant absorption, cf. solar • corona (Ionson 78, Hollweg 87, • Steinolfson 85, etc…..) Resonant Layer

  10. Initial-value problem: toy model, zero friction 1 kg 10000 small oscillators, 0.01g

  11. Zoom in on the residual:

  12. Zoom in on the residual: Power spectrum: 2 Oscillations !!! But: edges of the continuum Energies of small oscillators

  13. Phases of small oscillators: Special Point!

  14. Initial-value problem: inflected spectrum 1 kg 10000 small oscillators, 0.01g

  15. The real magnetar (simulated)!

  16. The real magnetar (simulated)!

  17. Dynamical spectrum (simulations)

  18. Dynamical spectrum (simulations)

  19. Dynamical spectrum theory

  20. Asteroseismology? • Low-frequency QPOs (18Hz) probe Alfven speed in the core. • For B=10 G, need to decouple 90% of the core material from the wave. Neutron superfluidity! 15

  21. Conclusions: main features of Quasi-Periodic Oscillations • Steady QPOs---special points of the Alfven continuum, • Intermittent QPOs everywhere, but enhanced near • crustal frequencies. • Qualitative agreement between theory and observations • Powerful probe of the Alfven speed in the interior of • magnetars • 5. Open issue: magnetosphere

  22. Part 2 Measuring gravitational waves using Pulsar Timing Arrays.

  23. Galaxy formation: White & Rees 78 Universe becomes matter-dominated at z=10000. Gravitational instability becomes effective. Small halos collapse first, small galaxies form first Smaler galaxies merge to form large spirals and ellipticals.

  24. Merging GalaxiesMerging SBHs? Komossa et al 02 (Chandra) Snijders & van der Werf 06

  25. Evidence for mergers? But: simulations Mass deficit at the center do not agree with observations: Milosavljevic & Merritt 01 Graham 04 McDermitt et al. 06 (Sauron)

  26. Q: What to do? A: Measure gravitational waves!

  27. LISA:the ESA/NASA space mission to detect gravitational waves. Binary black hole mergers Out to z=3 is one of the main targets Launch date 1915+..

  28. Detection Amplitude for SBH mergers at z=1. Unprecedented test of GR as dynamical theory of spacetime!

  29. Measuring gravitational-wave background with aPulsar Timing Array. Earth millisecond pulsar gravitational wave frequency shift arrival on Earth departure from pulsar

  30. Millisecond pulsars: • Excellent clocks. Current precision 1 microsecond, • projected precision ~100-200 ns. • Intrinsic noise unknown and uncorrelated. • GW noise uknown but correlated. Thus need to • look for correlations between different pulsars. • Many systematic effects with correlations: local • noisy clocks, ephemeris errors, etc. However, • GW signature is unique! 2 Pulsar Timing Arrays: Australia (20 pulsars) Manchester Europe (~20) Kramer+ Stappers

  31. John Rowe animation/ATNF, CSIRO

  32. Contributions to timing residuals: • Gravitational waves!! • Pulsar timing noises • Quadratic spindowns • Variations in the ISM • Clock noises • Earth ephemeris errors • Changes of equipment • Human errors Our work so far Optimistic esimate: ~5000 timing residuals from all pulsars.

  33. Gravitational waves (theory): Phinney 01 Jaffe & Backer 03 Wyithe & Loeb 03 -p S(f)=A f

  34. Current algorithm Jenet et al. 05 • <δt δt > = const·[6x log(x)-x+2], x=cos(ab) a b GW pulsar b pulsar a Look for correlation of this form! But: statistical significance? Parameter extraction?

  35. Leiden+CITA effort: van Haasteren, L., McDonald (CITA), Lu (CITA), soon tbs Gravitational-Wave signal extraction • Bayesian approach: • Parametrize simultaneously GW background and pulsar • noises (42 parameters) • Parametrize quadratic spindowns (60 parameters) • derive P(parameters|data), where data=5000 timing • residuals • marginalize numerically over pulsar noises and • analytically over the spindowns

  36. Advantages • No loss of information-optimal detection • Measures the amplitude AND the slope of GWB • Natural treatment of known systematic errors • Allows unevenly sampled data

  37. Markov Chain simulation: Pulsar noises 100 ns.

  38. Conclusions part 2: • SBH binaries predicted but not yet observed • Gravitational-wave detection by LISA and • Pulsar-Timing Arrays is likely within 1-1.5 decade.

  39. Type-I x-ray bursts. Spitkovsky, L., Ushomirsky 02 Spitkovsky & L., in prep Amsterdam, SRON, NASA, MIT,.. accretion X-ray flux H+He He THERMONUCLEAR BOMB ! ashes time ashes 1 sec

  40. Analogy to hurricanes

  41. FLAMES deflagration fuel front heat heat propagation speed of the flame rise time of the burst reaction speed Heat propagation: 1. microscopic conduction: too slow, 10 m/sec Niemayer 2000 2. turbulence from buoyant convection (Fryxell, Woosley): • highly uncertain; only upper limit works • probably irrelevant!

  42. HEAT PROPAGATION • Kelvin-Helmholtz stable!! • Baroclinic: unstable but weak. • Heat conduction a la Niemeier, • but across a huge interface! 30m hot cold 3m 3 km Rossby radius

  43. ROSSBY RADIUS Scale where potential = kinetic energy Rossby radius aRis a typical size of synoptic motions on Earth: ~1000 km, on NS ~ 1km

  44. TWO-LAYERSHALLOW-WATER MODEL 2 h2(x) Q(T) h1(x) 1 Heat Q(T): Temperature -- height: Two sets of coupled shallow-water equations in 1 1/2 D. Include mass and momentum transport across layers and interlayer friction

  45. Burst QPOs from ocean Rossby waves? Heyl 2004, Lee 2005, Piro & Bildsten 2005, Narayan & Cooper 2007 + QPO coherence, + QPOs in the tail - Typically, waves go too fast. - Not clear how to excite them. - What happens during the burst rise (i.e., spreading hot spot)?

  46. Conclusions: • Good prospects to understand magnetar QPOs and • to learn about neutron-star interior • 2. Good prospects to understand type-I burst deflagration, • but QPO behaviour, etc., very difficult to understand

  47. Precession of radio pulsars. Theory: radio pulsars cannot precess slowly Shaham 1977 Fast precession: 1/100 of NS spin pinned superfluid vortices Observations: Pulsar PSR B1828 Stairs et al 2000 Spin period 0.5 seconds Precession period 500 days Shaham’s nightmare!! No strong pinning in the crust? Link & Cutler 03 Jones 98

More Related