Neutron Star Magnetic Mountains: An Improved Model

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Neutron Star Magnetic Mountains An Improved
Model
Orange 2009 Pulsar Meeting
Maxim Priymak Supervisor Dr. A. Melatos
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Overview

• Accreting Neutron Stars (NS) as Gravitational
  Wave (GW) sources
• Magnetic mountain mechanism
• Improved magnetic mountain model
• Implemented more realistic EoS
• GW detectability decreases

• Motivation
• Quantify GW detectability of accreting NS by
  LIGO/ALIGO
• Construct GW search templates
• Infer NS properties (Maccreted, conductivity etc)

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Accreting Neutron Stars

• Accreting Neutron Stars (NS)
• X-ray sources (LMXB/HMXB)
• NS spin up
• NS spin measurements
• X-ray pulsations/Burst oscillations/QPO
• Spin distribution cut off gt 700 Hz
• None at Obreak up (1500-3000 Hz)

• NOT a selection effect
• 2 mechanisms explain this
• Gravitational Wave (GW) emission
• Propeller effect
• Dominant mechanism Inconclusive
• both contribute

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Magnetic Mountain

• Current model deficiencies
• Rigid crust no sinking
• Irrotational no FCORIOLIS
• Constant BCs no crustal freezing
• Isothermal no variable resistivity
• No inclination unrealistic
• Ideal isothermal EoS (P cs2?)
  unrealistic

• Accretion driven (LMXB/HMXB)
• B confines matter
• 1) PHYDROSTATIC gt PMAGNETIC Matter
  Spreads
• 2) B distorted Equilibrium NS
  asphericity
• 4) Spin/Dipole axes misaligned Q ? 0
  GW
• Advantages (as GW emitter)
• Known position and/or signal f (X-ray / Optical /
  Radio) Persistent
• Current Models
• 2D (Payne Melatos 2004)
• Axisymmetric MHS equilibrium
• Stable
• 3D (Vigelius Melatos 2008)
• Non-ideal MHD
• Stable

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Solving the MHS equilibrium
Lorentz force (pressure tension)

• Supplemented with
• EoS
• Mass-flux Constraint dM/d?final dM/d?initial
  dM/d?accreted

Pressure gradient
Gravitational force
Net Force
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MHS Equilibrium Dipole Moment (µ) and
Ellipticity (e) versus Maccreted

• 2 Feasible EoS (P K?G)
• Degenerate Neutron EoS K 5.4e4 (SI), G 5/3
• Relativistic Degenerate Electron EoS K 4.9e9
  (SI), G 4/3
• (cf. Ideal Isothermal EoS P cs2? )

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MHS Equilibrium Bmax and ?max versus Maccreted

• Attained ?max realistic (cf. Ideal Isothermal
  EoS)
• Above Bcracking plastic flow ?

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Magnetic Mountain Ideal Isothermal EoS
Maccreted 3.3x10-5 M?
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Magnetic Mountain Adiabatic EoS
Degenerate n EoS
Maccreted 3.3x10-7 M?
Degenerate Relativistic e- EoS
Maccreted 3.3x10-8 M?
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LIGO/ALIGO Estimates

• GW strain h is

Ma 10-4 M?
Ohmic diffusion arrests mountain growth
Ma 10-5 M?
Ma 10-6 M?
Ma 10-7 M?
Ma 10-8 M?
Ma 10-9 M?
No observed NS that spin fast enough
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Current Work

• Extend to realistic Maccreted
• Implement Realistic Nuclear EoS

Future Work

• Crustal freezing / sinking
• Compute feedback b/w mountain and magnetosphere
  Cornell Collaboration
• Application to X-ray bursts
• Light curves cyclones / Episodic decay of the
  mountain
• WHY?
• Quantify the effects on GW detectability by
  LIGO/ALIGO
• Construct GW search templates
• Infer NS properties (Maccreted, conductivity etc)

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The End
Thank you for your attention.
Any Questions?