Gravitational Radiation from an Accreting Millisecond Pulsar with a Magnetically Confined Mountain

By Matthias Vigelius, D. Payne, Andrew Melatos. 2005

137 citations recorded by the source corpus.

The amplitude of the gravitational radiation from an accreting neutron star undergoing polar magnetic burial is calculated. During accretion, the magnetic field of a neutron star is compressed into a narrow belt at the magnetic equator by material spreading equatorward from the polar cap. In turn, the compressed field confines the accreted material in a polar mountain, which is generally misaligned with the rotation axis, producing gravitational waves. The equilibrium hydromagnetic structure of the polar mountain, and its associated mass quadrupole moment, are computed as functions of the accreted mass Ma by solving a Grad-Shafranov boundary value problem. The orientation- and polarization-averaged gravitational wave strain at Earth is found to be hc = 6 × 10-24(Ma/Mc)(1 + Mab2/8Mc)-1(f/0.6 kHz)2(d/1 kpc)-1, where f is the wave frequency, d is the distance to the source, b is the ratio of the hemispheric to polar magnetic flux, and the cutoff mass Mc ~ 10-5 M☉ is a function of the natal magnetic field, temperature, and electrical conductivity of the crust. This value of hc exceeds previous estimates that failed to treat equatorward spreading and flux freezing self-consistently. It is concluded that an accreting millisecond pulsar emits a persistent, sinusoidal gravitational wave signal at levels detectable, in principle, by long-baseline interferometers after phase-coherent integration, provided that the polar mountain is hydromagnetically stable. Magnetic burial also reduces the magnetic dipole moment μ monotonically as μ ∝ (1 + 3Ma/4Mc)-1, implying a novel, observationally testable scaling hc(μ). The implications for the rotational evolution of (accreting) X-ray and (isolated) radio millisecond pulsars are explored.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/042f0febf8a1e2808f2b16e5bec16720a02337f9

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Citations in the corpus

Detecting gravitational wave emission from the known accreting neutron stars (2008, background): “…a quadrupolar asymmetry that leads to gravitational wave (GW) emission: crustal mountains (Bildsten 1998; Ushomirsky, Cutler & Bildsten 2000; Melatos & Payne 2005; Payne & Melatos 2006; Haskell, Jones & Andersson 2006), magnetic deformation (Cutler 2002; Haskell et al. 2008) or internal…”
Modelling magnetically deformed neutron stars (2007, background): “Finally, Melatos & Payne (2005) have studied the closely related problem of magnetically confined accretion, which may lead to large deformations.”
Thermonuclear Burst Oscillations (2012, background): “…the nature of possible gravitational wave generation mechanisms, such as crustal mountains (Bildsten 1998a; Ushomirsky, Cutler & Bildsten 2000; Melatos & Payne 2005; Haskell, Jones & Andersson 2006), or internal r-mode oscillations (Bildsten 1998a; Andersson, Kokkotas & Stergioulas 1999;…”
Gravitational Waves from Neutron Stars: A Review (2015, background): “…stellar deformations considerably larger than those due to the background magnetic field inferred from the external, dipole (Payne & Melatos 2004; Melatos & Payne 2005; Vigelius & Melatos 2009), which may even generate gravitational waves detectable by aLIGO or the Einstein Telescope (Priymak,…”