Poster abstract details
Lense-Thirring Precession Around Neutron Stars with Known Spin
Abstract
Quasi periodic oscillations (QPOs) between 300 and 1200 Hz in the X-ray emission from
low mass X-ray binaries have been linked to Keplerian orbital motion at the inner edge
of accretion disks. Lense-Thirring precession is precession of the line of nodes of inclined
orbits with respect to the equatorial plane of a rotating object due to the general rela-
tivistic effect of frame dragging. The Lense-Thirring model of Stella and Vietri (1998)
explains QPOs observed in neutron star low mass X-ray binaries at frequencies of a few
tens of Hz by the nodal precession of the orbits at the inner disk edge at a precession
frequency, νLT , identical to the Lense-Thirring precession of a test particle orbit. A
quadratic relation between νLT and the Keplerian orbital frequency, and a linear depen-
dence on spin frequency are predicted.
In early work (van Straaten et al., 2003) this quadratic relation was confirmed to remark-
able precision in three objects of uncertain spin. Since the initial work, many neutron
star spin frequencies have been measured in X-ray sources that show QPOs at both low
and high frequency.
Using archival data from the Rossi X-ray Timing Explorer, we compare the Lense-
Thirring prediction to the properties of quasi periodic oscillations measured in a sample
of 19 low mass X-ray binaries with known neutron star spin frequencies that are known
to show QPOs in their X-ray emission.
We find that in the range predicted for the precession frequency, we can distinguish two
different oscillations. In previous works, these two oscillations have often been confused.
The Lense-Thirring precession model is inconsistent with the observed frequencies, as
the required specific moment of inertia of the neutron star exceeds values predicted for
realistic equations of state. Also, we find correlations characterized by power laws with
indices that differ significantly from the prediction of 2.0. We find no evidence that the
neutron star spin frequency affects the QPO frequencies.
low mass X-ray binaries have been linked to Keplerian orbital motion at the inner edge
of accretion disks. Lense-Thirring precession is precession of the line of nodes of inclined
orbits with respect to the equatorial plane of a rotating object due to the general rela-
tivistic effect of frame dragging. The Lense-Thirring model of Stella and Vietri (1998)
explains QPOs observed in neutron star low mass X-ray binaries at frequencies of a few
tens of Hz by the nodal precession of the orbits at the inner disk edge at a precession
frequency, νLT , identical to the Lense-Thirring precession of a test particle orbit. A
quadratic relation between νLT and the Keplerian orbital frequency, and a linear depen-
dence on spin frequency are predicted.
In early work (van Straaten et al., 2003) this quadratic relation was confirmed to remark-
able precision in three objects of uncertain spin. Since the initial work, many neutron
star spin frequencies have been measured in X-ray sources that show QPOs at both low
and high frequency.
Using archival data from the Rossi X-ray Timing Explorer, we compare the Lense-
Thirring prediction to the properties of quasi periodic oscillations measured in a sample
of 19 low mass X-ray binaries with known neutron star spin frequencies that are known
to show QPOs in their X-ray emission.
We find that in the range predicted for the precession frequency, we can distinguish two
different oscillations. In previous works, these two oscillations have often been confused.
The Lense-Thirring precession model is inconsistent with the observed frequencies, as
the required specific moment of inertia of the neutron star exceeds values predicted for
realistic equations of state. Also, we find correlations characterized by power laws with
indices that differ significantly from the prediction of 2.0. We find no evidence that the
neutron star spin frequency affects the QPO frequencies.