Observation of neutron stars
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Observation of Neutron Stars. Kazuo Makishima Department of Physics, University of Tokyo [email protected] 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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Observation of neutron stars

Observation of Neutron Stars

Kazuo Makishima

Department of Physics,

University of Tokyo

[email protected]

Let’s enjoy physics….

Strongly-Correlated Many-Body Systems


Topics with nss

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


Birth and death of stars

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


Mass radius relations of stars

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


Synthesis of carbon

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


White dwarfs 1

“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


White dwarfs 2

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


Neutron stars

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


The ns interior

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


Neutron star population

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


The king of nss the crab pulsar

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


How to measure the ns mass

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


How to measure the ns radius

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


Atmospheric transparency for em waves

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


Japanese x ray satellites

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


Suzaku launch

Suzaku Launch

Strongly-Correlated Many-Body Systems


How to measure the ns mag field

How To Measure the NS Mag. Field

(1) A simple-minded estimate; flux conservation from the progenitor starR〜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


An accretion powered x ray pulsar xrp

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


Cyclotron resonances in xrps 1

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


Cyclotron resonances in xrps 2

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


Higher harmonic resonances

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


Distribution of magnetic fields

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


The origin of ns magnetic field

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


The origin of ns magnetic field1

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


Ferro magnetic and para magnetic nss

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


Magnetars

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


Enigmatic hard x rays from axps

Enigmatic Hard X-rays from AXPs

Den Hartog et al. (2006)

Strongly-Correlated Many-Body Systems


Diagnosing accretion column

Diagnosing Accretion Column

Strongly-Correlated Many-Body Systems


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