The Ultraluminous State

By T. Roberts, J. Gladstone, L. M. Hetf, C. Done, S. Vaughan. 2009

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Although a great deal of progress has been made towards understanding the nature of ultraluminous X‐ray sources (ULXs) over the past decade, many basic issues remain to be settled. Chief amongst these is the mass of the accretor in these systems: what proportion of ULXs are powered by accretion onto an intermediate‐mass black hole (IMBH), and how big are these objects? Or can we explain their extraordinary X‐ray luminosities by exotic, extreme accretion rate processes onto more prosaic stellar‐mass black holes? Here we report the results of two new studies using the best available XMM‐Newton observations to probe the astrophysics of ULXs. A systematic study of ULX power spectra shows a significant proportion of luminous objects with unusually suppressed variability compared to standard black hole binaries and AGN. Furthermore, detailed spectral studies confirm that ULX spectra appear unlike any standard accretion state in the XMM‐Newton band pass. Hence we infer that many ULXs contain small black holes op...

Subfields: Astronomy and Astrophysics, Biomedical Engineering

View Paper: https://www.semanticscholar.org/paper/18f84611387191616318b20b3534eda203a883dc

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A COMPLETE SAMPLE OF ULTRALUMINOUS X-RAY SOURCE HOST GALAXIES (2011, background): “…appropriate and have to be replaced by geometrically thicker disks (e.g., slim disks; Abramowicz et al. 1988; Kawaguchi 2003; Poutanen et al. 2007; Gladstone et al. 2009) with massive outflows.5 This introduces the possibility of mild geometrical beaming inside a conical outflow (King 2009, and…”
SUPER-CRITICAL GROWTH OF MASSIVE BLACK HOLES FROM STELLAR-MASS SEEDS (2014, background): “Super-critical accretion onto stellarmass black holes has been invoked to explain the nature of the ultraluminous X-ray sources (ULXs) (e.g. Gladstone et al. 2009; Middleton et al. 2013).”
Observational evidence for intermediate-mass black holes (2017, positive): “…et al. 2015) weakened the interpretation of a standard BH with an intermediate mass and supported the scenario in which most ULXs (those with X-ray luminosities < 5 × 1040 erg s−1) are stellar-mass BHs in superEddington accretion regimes (known as the ultraluminous state; Gladstone et al. 2009).”
A GLOBAL THREE-DIMENSIONAL RADIATION MAGNETO-HYDRODYNAMIC SIMULATION OF SUPER-EDDINGTON ACCRETION DISKS (2014, background): “Also, many of these sources have distinctive spectral features that differentiate them from normal X-ray binaries (Gladstone et al. 2009; Sutton et al. 2013; Walton et al. 2014; Rana et al. 2014), which are known to be accreting below the Eddington rate.”
THE NUCLEAR SPECTROSCOPIC TELESCOPE ARRAY (NuSTAR) HIGH-ENERGY X-RAY MISSION (2013, background): “Hypotheses are that ULXs contain stellar mass BHs in an extreme version of the very high state of Galactic BHs – the ‘ultra-luminous’ or wind-dominated state (Gladstone et al. 2009).”
The ultraluminous state revisited: fractional variability and spectral shape as diagnostics of super-Eddington accretion (2013, methodology): “This is motivated by the work of Gladstone et al. (2009): in their work the disc-like spectra had relatively warm discs in this model (kTin > 0.5 keV), whereas the hard and soft ultraluminous spectra had cool discs and were themselves differentiated by their value of photon index .”
Stellar black holes at the dawn of the universe (2011, background): “It is believed that the majority of ultraluminous X-ray sources (ULXs) found in external galaxies are HMXBs that contain black holes accreting at super-Eddington rates (Gladstone et al. 2009).”
What drives the growth of black holes (2011, background): “ULXs likely comprise a heterogenous population (see King et al. 2001; Begelman 2002; Roberts 2007 and Gladstone et al. 2009 for a broader discussion of the nature of ULXs), of which a sizeable fraction are stellar-mass BHs accreting at super-Eddington rates.”
Ultraluminous X-ray sources in the Chandra and XMM-Newton era (2011, methodology): “Other authors (Roberts 2007; Soria 2007; Gladstone et al. 2009; Weng & Zhang 2011) have suggested that the soft excess does come from the disk surface, but much further away than the innermost stable orbit, where the disk may be obscured or replaced by an outflow or a scattering corona (Section…”
GLOBAL STRUCTURE OF THREE DISTINCT ACCRETION FLOWS AND OUTFLOWS AROUND BLACK HOLES FROM TWO-DIMENSIONAL RADIATION-MAGNETOHYDRODYNAMIC SIMULATIONS (2011, background): “Comparison with Observations: Spectra Our model A might resolve the outstanding issue regarding the central engine of ULXs.”
Discovery of pulsations from NGC 300 ULX1 and its fast period evolution (2018, background): “Similar models have been successfully used to model the spectra of ULXs hosting neutron stars (Israel et al. 2017b; Pintore et al. 2017).”