Related papers: Spectroscopic comparison between ultraluminous X-r…
Ultraluminous X-ray sources (ULXs) are interesting systems as they can host intermediate mass black holes. Alternatively, ULXs can represent stellar-mass black holes accreting at super-Eddington rates. Recently spectral curvature or breaks…
Gravitational waves from the binary black hole (BH) merger GW150914 may enlighten our understanding of ultra-luminous X-ray sources (ULXs), as BHs>30Msun can reach luminosities>4x10^39 erg s^-1 without exceeding their Eddington limit. It is…
Discovery of coherent pulsations from several ultraluminous X-ray pulsars (ULXPs) has provided direct evidence of super-critical accretion flow. However, geometrical structure of such accretion flow onto the central neutron star remains…
We report X-ray spectral variability in an ultraluminous X-ray source NGC 1042 ULX1, using archival XMM-Newton and recent NuSTAR observations. In long-term evolution, the source has shown a trend of variation in spectral hardness. The…
Despite two decades of studies, it is still not clear whether ULX spectral transitions are due to stochastic variability in the wind or variations in the accretion rate or in the source geometry. The compact object is also unknown for most…
Two {\it ASCA} observations were made of two ultra-luminous compact X-ray sources (ULXs), Source 1 and Source 2, in the spiral galaxy IC 342. In the 1993 observation, Source 2 showed a 0.5--10 keV luminosity of $6 \times 10^{39}$ ergs…
Ultraluminous X-ray sources (ULXs) with neutron star (NS) accretors challenge traditional accretion models, and have sparked a debate regarding the role of geometrical beaming and strong magnetic fields (B). The reduction of the Thomson…
We have analyzed an XMM-Newton observation of the nearby spiral galaxy NGC 1313, which contains two "ultra-luminous" X-ray (ULX) sources. We measure isotropic luminosities of L_X = 2.0 * 10^(40) erg/s and L_X = 6.6 * 10^(39) erg/s for NGC…
The study of ultraluminous X-ray sources (ULXs) has changed dramatically over the last decade. In this review we first describe the most important observations of ULXs in various wavebands, and across multiple scales in space and time. We…
Ultra-luminous X-ray sources (ULXs) are high-mass X-ray binaries with an X-ray luminosity above $10^{39}$ erg s$^{-1}$. These ULXs can be powered by black holes that are more massive than $20M_\odot$, accreting in a standard regime, or…
Ultraluminous supersoft sources (ULSs) are defined by a thermal spectrum with colour temperatures ~0.1 keV, bolometric luminosities ~ a few 10^39 erg/s, and almost no emission above 1 keV. It has never been clear how they fit into the…
Ultraluminous X-ray bursts (hereafter ULXBs) are ultraluminous X-ray flares with a fast rise ($\sim$ one minute) and a slow decay ($\sim$ an hour), which are commonly observed in extragalactic globular clusters. Most ULXBs are observational…
High mass accretion rate onto strongly magnetised neutron stars results in the appearance of accretion columns supported by the radiation pressure and confined by the strong magnetic field of a star. At mass accretion rates above $\sim…
Ultraluminous X-ray sources (ULXs) are some of the brightest phenomena found outside of a galaxy's nucleus, and their explanation typically invokes accretion of material onto a black hole. Here, we perform the largest population study to…
The presence of radiatively driven outflows is well established in ultraluminous X-ray sources (ULXs). These outflows are optically thick and can reprocess a significant fraction of the accretion luminosity. Assuming isotropic emission,…
The Ultra Luminous X-ray Sources (ULXs) are unique in exhibiting moderately bright X-ray luminosities, $L_{\rm x} \sim 10^{38-40} {\rm erg~s^{-1}}$, and relatively high blackbody temperatures, $\Tin \sim 1.0-2.0 {\rm keV}$. From the…
To reconcile the observed unusual high luminosity of NuSTAR X-ray pulsations from M82X-2 with the most extreme violation of the Eddington limit, and in view that the persistent X-ray radiation from M82X-2 almost precludes the possibility of…
We report the results of Chandra and XMM-Newton observations of a new outburst of an ultra-luminous X-ray source in M101. During a Chandra monitoring observation of M101, M101 ULX-1 was found to be in outburst in 2004 December, the second…
Optical studies of ultraluminous X-ray sources (ULX) in nearby galaxies have turned out to be instrumental in discriminating between various models including the much advertised intermediate mass black hole hypothesis and various beaming…
Multiwavelength observations may help us understand the physical nature of the ultraluminous X-ray sources (ULXs) found in external galaxies. Enabled by the arcsecond X-ray source positions now available from Chandra, there has been…