Gravitational waves from pulsars: Emission by the magnetic field induced distortion

Nov, 1995
17 pages
Published in:
  • Astron.Astrophys. 312 (1996) 675
e-Print:

Citations per year

1995200320112019202505101520
Abstract: (arXiv)
The gravitational wave emission by a distorted rotating fluid star is computed. The distortion is supposed to be symmetric around some axis inclined with respect to the rotation axis. In the general case, the gravitational radiation is emitted at two frequencies: Ω\Omega and 2Ω2\Omega, where Ω\Omega is the rotation frequency. The obtained formul\ae\ are applied to the specific case of a neutron star distorted by its own magnetic field. Assuming that the period derivative P˙\dot P of pulsars is a measure of their magnetic dipole moment, the gravitational wave amplitude can be related to the observable parameters PP and P˙\dot P and to a factor β\beta which measures the efficiency of a given magnetic dipole moment in distorting the star. β\beta depends on the nuclear matter equation of state and on the magnetic field distribution. The amplitude at the frequency 2Ω2\Omega, expressed in terms of PP, P˙\dot P and β\beta, is independent of the angle α\alpha between the magnetic axis and the rotation axis, whereas at the frequency Ω\Omega, the amplitude increases as α\alpha decreases. The value of β\beta for specific models of magnetic field distributions has been computed by means of a numerical code giving self-consistent models of magnetized neutron stars within general relativity. It is found that the distortion at fixed magnetic dipole moment is very dependent of the magnetic field distribution; a stochastic magnetic field or a superconductor stellar interior greatly increases β\beta with respect to the uniformly magnetized perfect conductor case and might lead to gravitational waves detectable by the VIRGO or LIGO interferometers. The amplitude modulation of the signal induced by the daily rotation of the Earth has been computed and specified to the case of the Crab pulsar and VIRGO
Note:
  • 17 pages, 12 PostScript figures, accepted for publication in Astronomy & Astrophysics
  • gravitational radiation
  • pulsar
  • magnetic field
  • n: matter
  • matter: fluid
  • counters and detectors: interference
  • numerical calculations