X-ray observations of ultraluminous X-ray sources

Roberts, T. P.

doi:10.1007/s10509-007-9547-z

Cited by 177 publications

(198 citation statements)

References 84 publications

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“…In the last decade it has been proposed that a substantial fraction of the population of ultraluminous X-ray sources (ULXs) and ultraluminous supersoft sources (ULSs) are powered by super-Eddington accretion onto compact objects such as neutron stars and black holes (see, e.g., King et al 2001, Roberts 2007, Urquhart and Soria 2016, Feng et al 2016, and references therein). In particular, ULSs could be a category of ULXs observed at high inclination angles, possibly edge on, where a thick layer of material is obscuring the innermost hard X-ray emitting regions (e.g., Kylafis &Xilouris 1993 andPoutanen et al 2007).…”

Section: Discussionmentioning

confidence: 99%

From ultraluminous X-ray sources to ultraluminous supersoft sources: NGC 55 ULX, the missing link

Pinto

Alston

Soria

et al. 2017

Monthly Notices of the Royal Astronomical Society

123

188

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In recent work with high-resolution grating spectrometers (RGS) aboard XMM-Newton Pinto et al. (2016) have discovered that two bright and archetypal ultraluminous X-ray sources (ULXs) have strong relativistic winds in agreement with theoretical predictions of high accretion rates. It has been proposed that such winds can become optically thick enough to block and reprocess the disk X-ray photons almost entirely, making the source appear as a soft thermal emitter or ultraluminous supersoft Xray source (ULS). To test this hypothesis we have studied a ULX where the wind is strong enough to cause significant absorption of the hard X-ray continuum: NGC 55 ULX. The RGS spectrum of NGC 55 ULX shows a wealth of emission and absorption lines blueshifted by significant fractions of the light speed (0.01 − 0.20)c indicating the presence of a powerful wind. The wind has a complex dynamical structure with the ionization state increasing with the outflow velocity, which may indicate launching from different regions of the accretion disk. The comparison with other ULXs such as NGC 1313 X-1 and NGC 5408 X-1 suggests that NGC 55 ULX is being observed at higher inclination. The wind partly absorbs the source flux above 1 keV, generating a spectral drop similar to that observed in ULSs. The softening of the spectrum at lower (∼ Eddington) luminosities and the detection of a soft lag agree with the scenario of wind clumps crossing the line of sight, partly absorbing and reprocessing the hard X-rays from the innermost region.

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Section: Discussionmentioning

confidence: 99%

From ultraluminous X-ray sources to ultraluminous supersoft sources: NGC 55 ULX, the missing link

Pinto

Alston

Soria

et al. 2017

Monthly Notices of the Royal Astronomical Society

123

188

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“…Indeed, a number of other ULXs showed similar degeneracies between spectral shape, luminosity and short-term variability when comparing low and highquality data, and it has been proposed that these ULXs may be sMBHs or massive stellar BHs accreting at super-Eddington rates (e.g. Stobbart et al 2006;Roberts 2007;Gladstone et al 2009;Heil et al 2009;Middleton et al 2011;Sutton et al 2013b;Pintore et al 2014;Middleton et al 2015). If the power-law-dominated spectra of NGC 5643 ULX1 are indeed simply due to the poor data quality and the intrinsic spectra are actually similar to the highest quality observation, then the marginally different levels of short-term variability could be explained by the effects of an outflow ejected by the accretion disc at radii where it is locally super-Eddington (Poutanen et al 2007;Ohsuga & Mineshige 2011;Takeuchi et al 2014).…”

Section: Discussionmentioning

confidence: 99%

“…As these features are not commonly observed in Galactic XRBs, they imply a new spectral regime, which is usually referred to as the 'ultraluminous state' (Roberts 2007;Gladstone et al 2009), and may be associated with super-Eddington accretion. A few luminous ULXs have very recently been observed with NuSTAR, resulting in spectra which demonstrate that the highenergy curvature persists above 10 keV (Bachetti et al 2013;Walton et al 2013a;Rana et al 2015), confirming this result.…”

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confidence: 99%

The ultraluminous X-ray source NGC 5643 ULX1: a large stellar mass black hole accreting at super-Eddington rates?

Pintore

Zampieri

Sutton

et al. 2016

Mon. Not. R. Astron. Soc.

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A sub-set of the brightest ultraluminous X-ray sources (ULXs), with X-ray luminosities well above 10 40 erg s −1 , typically have energy spectra which can be well described as hard power-laws, and short-term variability in excess of ∼ 10%. This combination of properties suggests that these ULXs may be some of the best candidates to host intermediate mass black holes (IMBHs), which would be accreting at sub-Eddington rates in the hard state seen in Galactic X-ray binaries. In this work, we present a temporal and spectral analysis of all of the available XMM-Newton data from one such ULX, the previously poorly studied 2XMM J143242.1−440939, located in NGC 5643. We report that its high quality EPIC spectra can be better described by a broad, thermal component, such as an advection dominated disc or an optically thick Comptonising corona. In addition, we find a hint of a marginal change in the short-term variability which does not appear to be clearly related to the source unabsorbed luminosity. We discuss the implications of these results, excluding the possibility that the source may be host an IMBH in a low state, and favouring an interpretation in terms of super-Eddington accretion on to a black hole of stellar origin. The properties of NGC 5643 ULX1 allow us to associate this source to the population of the hard/ultraluminous ULX class.

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“…ULXs were universally considered to be accreting black holes, most likely ∼ 10 M⊙ ones in a binary with a high-mass companion, with some sources possibly harbouring "intermediate mass" ∼ 10 2−3 M⊙ black holes (King et al 2001;Roberts 2007). Their high luminosity was thought to imply that if the X-ray source is of typical stellar mass, the emission should be beamed, perhaps in an accretion funnel.…”

Section: Introductionmentioning

confidence: 99%

An ultraluminous nascent millisecond pulsar

Kluźniak

Lasota

2015

Monthly Notices of the Royal Astronomical Society: Letters

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If the ultraluminous source (ULX) M82 X-2 sustains its measured spin-up value oḟ ν = 10 −10 s −2 , it will become a millisecond pulsar in less than 10 5 yr. The observed (isotropic) luminosity of 10 40 erg/s also supports the notion that the neutron star will spin up to a millisecond period upon accreting about 0.1 M ⊙ -the reported hard X-ray luminosity of this ULX, together with the spin-up value, implies torques consistent with the accretion disc extending down to the vicinity of the stellar surface, as expected for low values of the stellar dipole magnetic field (B 10 9 G). This suggests a new channel of millisecond pulsar formation-in high-mass X-ray binaries (HMXBs)-and may have implications for studies of gravitational waves, and possibly for the formation of low-mass black holes through accretion-induced collapse.

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X-ray observations of ultraluminous X-ray sources

Cited by 177 publications

References 84 publications

From ultraluminous X-ray sources to ultraluminous supersoft sources: NGC 55 ULX, the missing link

From ultraluminous X-ray sources to ultraluminous supersoft sources: NGC 55 ULX, the missing link

The ultraluminous X-ray source NGC 5643 ULX1: a large stellar mass black hole accreting at super-Eddington rates?

An ultraluminous nascent millisecond pulsar

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