Ultraluminous X-ray sources (ULXs) are accreting black holes that may contain the missing population of intermediate mass black holes or reflect super-Eddington accretion physics. Ten years of
...Chandra and
XMM-Newton observations of ULXs, integrated by multiband studies of their counterparts, have produced a wealth of observational data and phenomenological classifications. We review the properties of their host galaxies, list popular spectral models and implications for standard and supercritical accretion physics, demonstrate how X-ray timing of these objects places constraints on their masses. We also review multiwavelength studies of ULXs, including the optical emission of the binary system and nebulosity around them. We summarize that three classes of black holes could power ULXs: normal stellar mass black holes (∼10
M
⊙), massive stellar black holes (≲100
M
⊙), and intermediate mass black holes (10
2–10
4
M
⊙). We collect evidence for the presence of these three types of compact objects, including caveat of each interpretation, and briefly review their formation processes.
Abstract
We present general relativistic radiation magnetohydrodynamics simulations of super-Eddington accretion on a 10 M⊙ black hole. We consider a range of mass accretion rates, black hole spins ...and magnetic field configurations. We compute the spectra and images of the models as a function of viewing angle and compare them with the observed properties of ultraluminous X-ray sources (ULXs). The models easily produce apparent luminosities in excess of 1040 erg s−1 for pole-on observers. However, the angle-integrated radiative luminosities rarely exceed 2.5 × 1039 erg s−1 even for mass accretion rates of tens of Eddington. The systems are thus radiatively inefficient, though they are energetically efficient when the energy output in winds and jets is also counted. The simulated models reproduce the main empirical types of spectra – disc-like, supersoft, soft, hard – observed in ultraluminous X-ray sources (ULXs). The magnetic field configuration, whether ‘standard and normal evolution’ (SANE) or ’magnetically arrested disc’ (MAD), has a strong effect on the results. In SANE models, the X-ray spectral hardness is almost independent of accretion rate, but decreases steeply with increasing inclination. MAD models with non-spinning black holes produce significantly softer spectra at higher values of
$\dot{M}$
, even at low inclinations. MAD models with rapidly spinning black holes are unique. They are radiatively efficient (efficiency factor ∼10–20 per cent), superefficient when the mechanical energy output is also included (70 per cent) and produce hard blazar-like spectra. In all models, the emission shows strong geometrical beaming, which disagrees with the more isotropic illumination favoured by observations of ULX bubbles.
The M 101 galaxy contains the best-known example of an ultraluminous supersoft source (ULS), dominated by a thermal component at kT ≈ 0.1 keV. The origin of the thermal component and the relation ...between ULSs and standard (broad-band spectrum) ultraluminous X-ray sources are still controversial. We re-examined the X-ray spectral and timing properties of the M 101 ULS using archival Chandra and XMM–Newton observations. We show that the X-ray time-variability and spectral properties are inconsistent with standard-disc emission. The characteristic radius R
bb of the thermal emitter varies from epoch to epoch between ≈10 000 and ≈100 000 km; the colour temperature kT
bb varies between ≈50 and ≈140 eV and the two quantities scale approximately as
$R_{\rm bb} \propto T_{\rm bb}^{-2}$
. In addition to the smooth continuum, we also find (at some epochs) spectral residuals well fitted with thermal-plasma models and absorption edges: we interpret this as evidence that we are looking at a clumpy, multitemperature outflow. We suggest that at sufficiently high accretion rates and inclination angles, the supercritical, radiatively driven outflow becomes effectively optically thick and completely thermalizes the harder X-ray photons from the inner part of the inflow, removing the hard spectral tail. We develop a simple, spherically symmetric outflow model and show that it is consistent with the observed temperatures, radii and luminosities. A larger, cooler photosphere shifts the emission peak into the far-UV and makes the source dimmer in X-rays but possibly ultraluminous in the UV. We compare our results and interpretation with those of Liu et al.
Abstract
We present the results of our study of the luminous (
L
X
≈ 10
39
erg s
−1
) X-ray binary CXOU J121538.2+361921 in NGC 4214, the high-mass X-ray binary with the shortest known orbital ...period. Using Chandra data, we confirm the ≈13,000 s (3.6 hr) eclipse period, and an eclipse duration of ≈2000 s. From this, we estimate a mass ratio
M
2
/
M
1
≳ 3 and a stellar density
ρ
≈ 6 g cm
−3
, which implies that the donor must be a Wolf–Rayet or a stripped helium star. The eclipse egress is consistently much slower than the ingress. This can be explained by denser gas located either in front of the compact object (as expected for a bow shock) or trailing the donor star (as expected for a shadow wind, launched from the shaded side of the donor). There is no change in X-ray spectral shape with changing flux during the egress, which suggests either variable partial covering of the X-ray source by opaque clumps or, more likely, a gray opacity dominated by electron scattering in a highly ionized medium. We identify the optical counterpart from Hubble images. Photometry blueward of ∼5500 Å indicates a bright (
M
B
≈ −3.6 ± 0.3 mag, for a range of plausible extinctions), hot (
T
≈ 90,000 ± 30,000 K) emitter, consistent with the Wolf–Rayet scenario. There is also a bright (
M
I
≈ −5.2 mag), cool (
T
≈ 2700 ± 300 K) component consistent with an irradiated circumbinary disk or with a chance projection of an unrelated asymptotic giant branch star along the same line of sight.
ABSTRACT The mass scaling relation between supermassive black holes and their host spheroids has previously been described by a quadratic or steeper relation at low masses (105 < Mbh/M 107). How this ...extends into the realm of intermediate-mass black holes (102 < Mbh/M < 105) is not yet clear, although for the barred Sm galaxy LEDA 87300, Baldassare et al. recently reported a nominal virial mass of Mbh = 5 × 104 M residing in a "spheroid" of stellar mass equal to 6.3 × 108 M . We point out, for the first time, that LEDA 87300 therefore appears to reside on the near-quadratic Mbh-Msph,* relation. However, Baldassare et al. modeled the bulge and bar as the single spheroidal component of this galaxy. Here we perform a 3-component bulge+bar+disk decomposition and find a bulge luminosity which is 7.7 times fainter than the published "bulge" luminosity. After correcting for dust, we find that Mbulge = 0.9 × 108 M and Mbulge/Mdisk = 0.04-which is now in accord with ratios typically found in Scd-Sm galaxies. We go on to discuss slight revisions to the stellar velocity dispersion (40 11 km s−1) and black hole mass ( ) and show that LEDA 87300 remains consistent with the Mbh- relation, and also the near-quadratic Mbh-Msph,* relation when using the reduced bulge mass. LEDA 87300 therefore offers the first support for the rapid but regulated (near-quadratic) growth of black holes, relative to their host bulge/spheroid, extending into the domain of intermediate-mass black holes.
Black-hole accretion states near or above the Eddington luminosity (the point at which radiation force outwards overcomes gravity) are still poorly known because of the rarity of such sources. ...Ultraluminous X-ray sources are the most luminous class of black hole (LX 1040 erg s−1) located outside the nuclei of active galaxies. They are likely to be accreting at super-Eddington rates, if they are powered by black holes with masses less than 100 solar masses. They are often associated with shock-ionized nebulae, though with no evidence of collimated jets. Microquasars with steady jets are much less luminous. Here we report that the large nebula S26 (ref. 4) in the nearby galaxy NGC 7793 is powered by a black hole with a pair of collimated jets. It is similar to the famous Galactic source SS433 (ref. 5), but twice as large and a few times more powerful. We determine a mechanical power of around a few 1040 erg s−1. The jets therefore seem 104 times more energetic than the X-ray emission from the core. S26 has the structure of a Fanaroff-Riley type II (FRII-type) active galaxy: X-ray and optical core, X-ray hot spots, radio lobes and an optical and X-ray cocoon. It is a microquasar where most of the jet power is dissipated in thermal particles in the lobes rather than relativistic electrons.
Powerful relativistic jets are one of the main ways in which accreting black holes provide kinetic feedback to their surroundings. Jets launched from or redirected by the accretion flow that powers ...them are expected to be affected by the dynamics of the flow, which for accreting stellar-mass black holes has shown evidence for precession
due to frame-dragging effects that occur when the black-hole spin axis is misaligned with the orbital plane of its companion star
. Recently, theoretical simulations have suggested that the jets can exert an additional torque on the accretion flow
, although the interplay between the dynamics of the accretion flow and the launching of the jets is not yet understood. Here we report a rapidly changing jet orientation-on a time scale of minutes to hours-in the black-hole X-ray binary V404 Cygni, detected with very-long-baseline interferometry during the peak of its 2015 outburst. We show that this changing jet orientation can be modelled as the Lense-Thirring precession of a vertically extended slim disk that arises from the super-Eddington accretion rate
. Our findings suggest that the dynamics of the precessing inner accretion disk could play a role in either directly launching or redirecting the jets within the inner few hundred gravitational radii. Similar dynamics should be expected in any strongly accreting black hole whose spin is misaligned with the inflowing gas, both affecting the observational characteristics of the jets and distributing the black-hole feedback more uniformly over the surrounding environment
.
We investigated the time-variability and spectral properties of the eclipsing X-ray source Circinus Galaxy X-1 (GG X-1), using Chandra, XMM-Newton and ROSAT. We phase-connected the light curves ...observed over 20 yr, and we obtained a best-fitting period P = (25,970.0 0.1) s 7.2 hr, and a period derivative P ˙ P = ( 10.2 4.6 ) × 10 − 7 yr−1. The X-ray light curve shows asymmetric eclipses, with sharp ingresses and slow, irregular egresses. The eclipse profile and duration vary substantially from cycle to cycle. We show that the X-ray spectra are consistent with a power-law-like component, which is absorbed by neutral and ionized Compton-thin material, and by a Compton-thick, partial-covering medium, which is responsible for the irregular dips. The high X-ray/optical flux ratio rules out the possibility that CG X-1 is a foreground Cataclysmic Variable. In agreement with previous studies, we conclude that it is the first example of a compact ultraluminous X-ray source fed by a Wolf-Rayet star or stripped Helium star. Its unocculted luminosity varies between 4 × 1039 erg s−1 and 3 × 1040 erg s−1. Both the donor star and the super-Eddington compact object drive powerful outflows. We suggest that the occulting clouds are produced in the wind-wind collision region and in the bow shock in front of the compact object. Among the rare sample of Wolf-Rayet X-ray binaries, CG X-1 is an exceptional target for studies of supercritical accretion and close binary evolution; it is also a likely progenitor of gravitational wave events.
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