Analysis of Quasi-periodic Oscillations and Time Lag in Ultraluminous X-Ray Sources with XMM-Newton

Li, Zijian; Xiao, G. C.; Chen, Li; Zhang, Shu; Bu, Q. C.; Zhang, Liang; Ma, Xiang; Yan, Linyin; Qu, J. L.

doi:10.3847/1538-4357/aa6892

Cited by 2 publications

(2 citation statements)

References 49 publications

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“…To date, the strongest claim of a soft-lag from a ULX is that for NGC 5408 X-1 (see Heil & Vaughan 2010, De Marco et al 2013, Hernandez-Garcia et al 2015 with QPOs observed between 10 and 38 mHz (De Marco et al 2013) with the soft band (0.3-1 keV) lagging the hard band (1-7 keV) by ≈ 1.5-5s at the QPO frequency (we note that soft lags have been reported in other ULXs at candidate QPO frequencies - Li et al 2017). Spectral fitting using a multi-colour disc blackbody component (in XSPEC this is through use of the DISKBB set of models which do not include a colour temperature correction: Mitsuda et al 1984) implies the temperature of the soft X-ray component in NGC 5408 X-1 lies between ≈ 0.12 -0.23 keV (see Soria et al 2004;Strohmayer & Mushotzky 2007;Middleton et al 2014;2015a).…”

Section: Ngc 5408 X-1supporting

confidence: 52%

The Lense–Thirring timing-accretion plane for ULXs

Middleton

Fragile

Ingram

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Identifying the compact object in ultraluminous X-ray sources (ULXs) has to-date required detection of pulsations or a cyclotron resonance scattering feature (CRSF), indicating a magnetised neutron star. However, pulsations are observed to be transient and it is plausible that accretion onto the neutron star may have suppressed the surface magnetic field such that pulsations and CRSFs will be entirely absent. We may therefore lack direct means to identify neutron star systems whilst we presently lack an effective means by which to identify black hole ULXs. Here we present a possible method for separating the ULX population by assuming the X-ray, mHz quasi-periodic oscillations (QPOs) and day timescale periods/QPOs are associated with Lense-Thirring precession of the inflow and outflowing wind respectively. The precession timescales combined with the temperature of the soft X-ray component produce planes where the accretor mass enters as a free parameter. Depending on the properties of the wind, use of these planes may be robust to a range in the angular momentum (spin) and, for high accretion rates, essentially independent of the neutron star's surface dipole field strength. Our model also predicts the mHz QPO frequency and magnitude of the phase-lag imprinted due to propagation through the optically thick wind; in the case of NGC 5408 X-1 we subsequently infer a black hole mass and high spin. Finally, we note that observing secular QPO evolution over sufficient baselines may indicate a neutron star, as the precession responds to spin-up which is not readily observable for black hole primaries.

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Section: Ngc 5408 X-1supporting

confidence: 52%

The Lense–Thirring timing-accretion plane for ULXs

Middleton

Fragile

Ingram

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…NGC 5408 X-1 shows the highest frequency soft lag that occurs at the same frequency as a broad quasi-periodic oscillation (QPO; Heil & Vaughan 2010;De Marco et al 2013;Li et al 2017). No such QPOs are found at the timescales of the soft lags in NGC 55 X-1 or here in NGC 1313 X-1, although in NGC 1313 X-1 the lag occurs over a broad frequency range, and so we cannot rule out that there is a broad Lorentzian in the power spectrum over this frequency range.…”

Section: Comparison To Other Ulxsmentioning

confidence: 99%

Discovery of a soft X-ray lag in the ultraluminous X-ray source NGC 1313 X-1

Kara

Pinto

Walton

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Ultraluminous X-ray Sources (ULXs) provide a unique opportunities to probe the geometry and energetics of super-Eddington accretion. The radiative processes involved in super-Eddington accretion are not well understood, and so studying correlated variability between different energy bands can provide insights into the causal connection between different emitting regions. We present a spectral-timing analysis of NGC 1313 X-1 from a recent XMM-Newton campaign. The spectra can be decomposed into two thermal-like components, the hotter of which may originate from the inner accretion disc, and the cooler from an optically thick outflow. We find correlated variability between hard (2-10 keV) and soft (0.3-2 keV) bands on kilosecond timescales, and find a soft lag of ∼ 150 seconds. The covariance spectrum suggests that emission contributing to the lags is largely associated with the hotter of the two thermal-like components, likely originating from the inner accretion flow. This is only the third ULX to exhibit soft lags. The lags range over three orders of magnitude in amplitude, but all three are ∼ 5 to ∼ 20 percent of the corresponding characteristic variability timescales. If these soft lags can be understood in the context of a unified picture of ULXs, then lag timescales may provide constraints on the density and extent of radiatively-driven outflows.

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Analysis of Quasi-periodic Oscillations and Time Lag in Ultraluminous X-Ray Sources with XMM-Newton

Cited by 2 publications

References 49 publications

The Lense–Thirring timing-accretion plane for ULXs

The Lense–Thirring timing-accretion plane for ULXs

Discovery of a soft X-ray lag in the ultraluminous X-ray source NGC 1313 X-1

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