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Observation of Neutron Stars

Observation of Neutron Stars. Kazuo Makishima Department of Physics, University of Tokyo maxima@phys.s.u-tokyo.ac.jp. Let’s enjoy physics…. Topics with NSs. Superfluid states, vorrtex strings Nuclear Pastas -- Dr. Sonoda Pion condensations in the central regions

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Observation of Neutron Stars

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  1. Observation of Neutron Stars Kazuo Makishima Department of Physics, University of Tokyo maxima@phys.s.u-tokyo.ac.jp Let’s enjoy physics…. Strongly-Correlated Many-Body Systems

  2. Topics with NSs • Superfluid states, vorrtex strings • Nuclear Pastas -- Dr. Sonoda • Pion condensations in the central regions • QGP, quark matter -- Prof.G. Baym • The origin of strong magnetic fields • … Strongly-Correlated Many-Body Systems

  3. H-fusion 1 0-４ 10 1 0-3 0.01 0.1 1 Supernova 10-４ 0.1 10-3 0.01 1 10 Nucleon degeneracy Birth and Death of Stars Initial Mas (M◎) ブラックホール Time Protostars Brown Dwarft Main Seq.Stars Planets classical gas pressure Coulomb repulsion Black Holes Red Giants N.S. White Dwarfs e-degeneracy Final Mas (M◎) Strongly-Correlated Many-Body Systems

  4. Grav.contraction evolution Chandrasekhar limit (M◎) 1 0-４ 1 0-3 0.01 0.1 1 Mass-Radius Relations of Stars Nucleons/Electrons=1.2 (H+He) 1 Main Seq.Stars Radius R (R◎) Planets Brown dwarfs 0.1 Uranus Jupiter Saturn Neptune R ∝ M1/3 0.01 White dwarfs Nucleons/Electrons=2.0 (He, C, O, ,,) 0.001 Mass M (M◎) Strongly-Correlated Many-Body Systems

  5. O7+ Ne8+ O6+ C5+ 0.3 0.5 1.0 1.5 Energy (keV) 13.6 eV×0.75×62 = 0.37 keV A dying star with a white dwarf forming at its core Suzaku soft X-ray spectrum (Murashima et al. 2006, ApJL) Synthesis of Carbon 106R◎ Optical (Hubble Sp.Telescope.) wind He burning (3α→12C) He H C/O ratio is ~90 times enhanced than the average cosmic matter Direct evidence of He→ C fusion C+O Strongly-Correlated Many-Body Systems

  6. “Gravitational fine structure constant” (by Prof. Y. Suto) A star of which the gravity is counter-balanced by the electron degenerate pressure M=WD mass, R=WD radius, n=particle density White Dwarfs (1) Fermi momentum Fermi energy (e-) Grav. Energy (p+) Virial theorem Strongly-Correlated Many-Body Systems

  7. Cancel out M◎ =2.0×1030 kg = solar mass If relativistic … White Dwarfs (2) Fermi momentum Fermi energy (e-) Grav. Energy (p+) Virial theorem Chandrasekhar mass = 1.47 M◎ Strongly-Correlated Many-Body Systems

  8. WDs Neutron Stars Change WDs to NSs, by changing electrons to nucleons RNS ~ (M/M◎)-1/3×10 km (corrected for gen. relativity & nuclear force) Strongly-Correlated Many-Body Systems

  9. The NS Interior “Outer Crust” Nuclei + electrons “Inner Crust” Nuclei, free neutrons, and electrons, possibly with “pasta” phases “Core” Uniform nuclear matter, possibly an exotic phase at the very center Magnetism provides one of the few diagnostic tools with which we can probe into the NS interior Strongly-Correlated Many-Body Systems

  10. Neutron Star Population 11 10 Magnetars? 10 10 Crab-like Pulsars 9 10 Binary X-ray Pulsars 8 10 7 Radio Pulsars 10 6 10 5 10 Surface Magnetic Field (T) Msec Pulsars Rotation Period (sec) 0.001 0.01 0.1 1 10 100 1000 Strongly-Correlated Many-Body Systems

  11. The remnant of the 1054 supernva. Emitting 30 Hz pulses from radio to gamma-ray energies, and accelerating particles to 1015 eV The King of NSs -- the Crab pulsar An X-ray view from Chandra Strongly-Correlated Many-Body Systems

  12. How To Measure the NS Mass Use radio pulsars in binary systems. Measure orbital Doppler effects of their radio pulses. Measure optical Doppler effects of their primary stars. Use Kepler’s law. Thorsett & Chakrabarty1999 Strongly-Correlated Many-Body Systems

  13. Luminosity 6 4 2 0 2.0 1.5 1.0 0.5 Temperature (keV) 15 10 5 0 Radius (km) 10 sec • Sometimes, a burst-like nuclear fusion (H → He or He→ C) occurs on a certain class of NSs. • The heated NS surface emits blackbody X-rays, and gradually cools down. • The blackbody temp. T and luminosity L can be measured. • Use Stefan-Boltzmann’s law to estimate the radius R How To Measure the NS Radius Measuring a NS radius is equiv. to measuring the size of a H-atom on Mt. Fuji from Tokyo Kuulkers & van der Klis (2000) Strongly-Correlated Many-Body Systems

  14. Ozone absorp. Blanket effect Free e- incoherent (Compton) Molecular(rot. vib.) Bound e-’s (photoelectric) Free e- coherent (plasma cutoff) Atmospheric Transparency for EM Waves Strongly-Correlated Many-Body Systems

  15. Hard X-ray Detector Hakucho (1979) Suzaku (Astro-E2) (2005 July 10) Tenma (1983) Japanese X-ray Satellites Ginga (1987) ASCA (1993) Strongly-Correlated Many-Body Systems

  16. Suzaku Launch Strongly-Correlated Many-Body Systems

  17. How To Measure the NS Mag. Field (1) A simple-minded estimate; flux conservation from the progenitor star R〜109m, B〜10-2 T →R〜104m, B〜108 T (2) Assuming –d(Iω2/2)/dt = mag. dipole radiation;→B∝ sqrt(P dP/dt) 〜 107-9 T (3) Detection of X-ray spectral features due to (electron) cyclotron resonance, or equivalently, transitions between Landau levels; Ea = hΩe = h(eB/me )=11.6 (B/108 T) keV Landau levels Electron cyclotorn frequency Strongly-Correlated Many-Body Systems

  18. An Accretion-Powered X-ray Pulsar (XRP) A supersonic accretion flow from companion A standing shock An X-ray emitting hot (kT~20 keV) accretion column A strongly magnetized NS with a rotation period of 0.1〜1000 sec, in a close binary with a mass-donating companion star. Electrons in the accretion column resonantly scatter X-ray photons, when they make transitions between adjacent Landau levels. → The X-ray spectrum will bear a strong spectral feature, called a Cyclotron Resonance Feature. A strongly magnetized NS Strongly-Correlated Many-Body Systems

  19. Cyclotron Resonances in XRPs (1) Counts/s/cm2/keV 2 5 10 20 50 100 Energy (keV) Before 1990, only two examples were known (Truemper et al. 1978) • A series of discoveries with the Ginga Satellite (Makishima et al. 1999) • A transient X-ray pulsar X0331+53 Makishima et al. (1990) • New measurements currently carried out with the Suzaku Hard X-ray Detector (e.g., Terada et al. 2006). Ea = 28 keV →B = 2.4×108 T Strongly-Correlated Many-Body Systems

  20. Cyclotron Resonances in XRPs (2) Her X-1 X0331+53 Cep X-4 Ea=33 keV Ea=28 keV Ea=29 keV 4U 0115+63 SMC X-1 4U 1538-52 12 & 23 keV Ea=21keV No feature Makishima et al. Astrophys. J. 525, 978 (1999) Strongly-Correlated Many-Body Systems

  21. Higher Harmonic Resonances Why is the 2nd harmonic deeper than the fundamental? • An absorbed 1Ω photons is soon re-emitted --> scattering • If a 2Ω photon is absorbed, the excited electron returns to g.s. by emitting two 1Ω photons in cascade--> pure absorption • The cascade photons will fill up the fundamental absorption. 4 harmonics in 4U 0115+63 Santangelo et al. (1998) 10 20 30 50 100 Energy (keV) Strongly-Correlated Many-Body Systems

  22. Distribution of Magnetic Fields log[ /(1+ z B )] (T) 10 8 6 4 2 0 2 20 10 100 5 50 9 8 BeppoSAX Ginga RXTE Suzaku HXD ASCA Number Surface magnetic fields of ~15 binary XRPs are tightly concentrated over (1-4)×108 T. (Makishima et al. 1999) Cyclotron Resonance Energy (keV) Strongly-Correlated Many-Body Systems

  23. The Origin of NS Magnetic Field +- ~A scenario before the 1990s ~ • All neutron stars are born with strong magnetic fields (〜108 T). • The magnetic field is sustained by permanent superconducting ring current in the crust. • The magnetic field decays exponentially with time, due to Ohmic loss of the ring current. • Radio pulsar statistics suggest a field decay timescale of τ〜107 yr. • The older NSs (e.g., millisecond pulsars) have the weaker magnetic fields. Strongly-Correlated Many-Body Systems

  24. The Origin of NS Magnetic Field +- N S ~A new scenario (Makishima et al. 1999) ~ If m.f. were decaying, the measured surface field would exhibit a continuous distribution toward lower fields --> contradict with the X-ray results. Strong-field and weak-field NSs are likely to be genetically different. Strong-field and weak-field objects are connected to each other by some phase transitions. → Magnetic field may be a manifestation of nuclear ferrro-magnetism. Strongly-Correlated Many-Body Systems

  25. Ferro-magnetic and para-magnetic NSs? N S Magnetic moments of neutrons may align due to exchange interaction, which must be repulsive on the shortest range. If all the neutrons align, we expect B〜 4×1012 T. • A small volume fraction (~10-4) is ferro-magnetic → strong-field NSs (108 T) • Entirely para-magnetic → weak-filed NSs (＜104~5 T) • Phase transitions may occur depending on, e.g., age, temperature, accretion history, etc. • A large fraction of the volume is ferro-magnetic → magnetars (1010~11 T) ? • The release of latent heat at the transition may explain some soft gamma-ray repeaters? Strongly-Correlated Many-Body Systems

  26. Magnetars Proton cyclotron rsonance E = 6.3 (B/1015G) [keV] SGR 1806-20 Ibrahim et al.(2002) • About two dozen X-ray pulsars, with periods of 6-12 sec, are known as Anomalous X-ray Pulsars (AXP). • Their spin-down rate, with plausible assumption, yields B~1011 T, but their X-ray luminosity >> kinetic energy output due to spin down. • They are rotating too slow to be rotation-powered, but they do not have companions (no accretion), either. • The only energy source is strong m.f. • Some of them are identified with “Soft Gamma-Ray Repeaters”, emitting enormous gamma-ray flasehs. Strongly-Correlated Many-Body Systems

  27. Enigmatic Hard X-rays from AXPs Den Hartog et al. (2006) Strongly-Correlated Many-Body Systems

  28. Diagnosing Accretion Column Strongly-Correlated Many-Body Systems

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