Testing the relativistic precession model using low-frequency and kHz quasi-periodic oscillations in neutron star low-mass X-ray binaries with known spin

Abstract

We analyze all available RXTE data on a sample of 13 low mass X-ray binaries with known neutron star spin that are not persistent pulsars. We carefully measure the correlations between the centroid frequencies of the quasi-periodic oscillations (QPOs). We compare these correlations to the prediction of the relativistic precession model (RPM) that, due to frame dragging, a QPO will occur at the Lense-Thirring precession frequency ν LT of a test particle orbit whose orbital frequency is the upper kHz QPO frequency ν u . Contrary to the most prominent previous studies, we find two different oscillations in the range predicted for ν LT that are simultaneously present over a wide range of ν u . Additionally, one of the low frequency noise components evolves into a (third) QPO in the ν LT range when ν u exceeds 600 Hz. The frequencies of these QPOs all correlate to ν u following power laws with indices between 0.4-3.3, significantly exceeding the predicted value of 2.0 in 80% of the cases (at 3 to >20σ ). Also, there is no evidence that the neutron star spin frequency affects any of these three QPO frequencies as would be expected for frame dragging. Finally, the observed QPO frequencies tend to be higher than the ν LT predicted for reasonable neutron star specific moment of inertia. In the light of recent successes of precession models in black holes, we briefly discuss ways in which such precession can occur in neutron stars at frequencies different from test particle values and consistent with those observed. A precessing torus geometry and other torques than frame dragging may allow precession to produce the observed frequency correlations, but can only explain one of the three QPOs in the ν LT range.

A review of quasi-periodic oscillations from black hole X-ray binaries: Observation and theory

“…Ingram and Done [86] later considered the precessing inner flow model, and found that the solid body precession frequency matched the LF QPO frequency if the surface density profile becomes more centrally peaked as the source gets brighter, as may result from material piling up on the MNS surface. More recently, van Doesburgh and van der Klis [240] considered a sample of 13 sources and again found that the surface density profile is required to become more centrally peaked as the source flux increases in order to explain the QPO frequencies. They additionally find that the LF QPO frequencies are higher than the precession frequencies produced by assuming reasonable moment of inertial values, and suggest (again) that the LF QPO fundamental could actually be twice the precession frequency, or that the precession is modified by mechanisms other than the frame dragging effect, such as radiation pressure and magnetic precession.…”

The highest frequency kHz QPOs in neutron star low-mass X-ray binaries

“…We plot hard colour vs. intensity, per observation, for 4U 1728-34 and 4U 0614+09 in Figures 2 and 3. We indicate the observations for which twin kHz QPOs and single kHz QPOs were reported with ν u >1000 Hz in van Doesburgh & van der Klis (2017). The observations with ν u >1200 Hz (pink) all have single kHz QPOs and low hard color.…”

“…8-2900, 4U 1636-53, 4U 1702-43 and 4U 1728-34; the NS spin frequency is known for these sources. SAX J1750-2900 and 4U 1636-53 were included in the study by van Doesburgh & van der Klis (2017), but no higher frequencies than reported in the literature were found. In Jonker et al (2001) it was suggested that the fractional rms of the kHz QPO is anti-correlated with source luminosity.…”

“…In that work, a large data set was uniformly processed for a different purpose than identifying the highest QPO frequencies. In view of the relevance of the issue of the highest frequency reliably detected for a kHz QPO, in this paper we present a detailed study of the QPO frequencies reported in van Doesburgh & van der Klis (2017), compare these to the literature (reanalyzing the data when necessary) and discuss implications for the supranuclear density equation of state and kHz QPO models.…”

Upper-twin-peak quasiperiodic oscillation in x-ray binaries and the energy from tidal circularization of relativistic orbits

“…Recent works have put forward strong evidence that the low frequency QPO seen in the BH LMXB H1743-322 is produced by frame dragging [14,15]. In the case of NS LMXBs, recent data analysis shows that the predic- * claudio.germana@gmail.com; claudio.germana@ufma.br tions of the modeling differ from the data because other factors may affect the modulation mechanism [16].…”