Gravitational radiation from accreting neutron stars
Andrew Melatos
University of Melbourne
The spin frequency distribution of neutron stars in low-mass X-ray binaries
(LMXBs) exhibits a sharp cut-off well below the centrifugal breakup
limit. If the cut-off is interpreted in terms of gravitational-wave
stalling, LMXBs should emit a relatively strong, periodic gravitational
wave signal detectable by the Laser Interferometer Gravitational Wave
Observatory (LIGO). LMXBs enjoy several advantages over binary inspirals:
they are persistent, their spin frequency and sky position are often
known in advance from X-ray observations, and they emit an approximately
"pure tone". One way to create the necessary nonaxisymmetry is to build
up a magnetically confined mountain by accretion onto the poles of
the star. In this talk, I present the latest results from theoretical
modelling of magnetic mountains. These include: equilibrium states in 2D
and 3D and their hydromagnetic stability, the role of resistive relaxation
and sinking, global oscillations of the mountain (and a new analytic
method for computing the continuous part of the oscillation spectrum),
the role of precession, and an updated detectability estimate for LIGO. I
report on the status of a radiometer search for magnetic mountains with
LIGO, and a search for precession in LMXBs in X-ray timing data from
the RXTE satellite. Current LIGO upper limits already place interesting
limits on the electrical resistivity of neutron star matter. The magnetic
mountain idea can be applied to understand several puzzling astrophysical
observations, e.g. the spin down of the accreting millisecond pulsar
J1808-3658, the very sinusoidal shape of oscillations in thermonuclear
X-ray bursts, and the polarisation swing in millisecond pulsars. I point
out several gaps in magnetic mountain modelling which need to be filled
in the future.
Date: | Lundi, le 15 septembre 2008 |
Heure: | 15:30 |
Lieu: | Université McGill |
| Ernest Rutherford Physics Building, R.E. Bell Conference Room (room 103) |
|