Related papers: X-ray Outflows and Super-Eddington Accretion in th…
We propose a geometrically thick, super-Eddington accretion disk model, where an optically thick wind is not necessary, to understand ultraluminous supersoft sources (ULSs). For high mass accretion rates $\dot M \ga 30\dot M_{\rm Edd}$ and…
The ultraluminous X-ray source (ULX) Holmberg II X-1 has been observed over 4 months in 2009/2010 by the Swift observatory. The source luminosity varied by a factor of up to 14, reaching a maximum 0.3-10 keV luminosity of ~3.0E40 erg/s. The…
With an inferred bolometric luminosity exceeding 10^42 erg/s, HLX-1 in ESO 243-49 is the most luminous of ultraluminous X-ray sources and provides one of the strongest cases for the existence of intermediate mass black holes. We obtain good…
We have analyzed the archival XMM-Newton data of the bright Ultra-Luminous X-ray Source (ULX) M82 X-1 with an 105 ksec exposure when the source was in the steady state. Thanks to the high photon statistics from the large effective area and…
Many upcoming surveys, particularly in the radio and optical domains, are designed to probe either the temporal and/or the spatial variability of a range of astronomical objects. In the light of these high resolution surveys, we review the…
We investigate the relationship between the hard X-ray photon index $\Gamma$ and the Eddington ratio ($\xi=L_{X}(0.5-25 \rm keV)/L_{Edd}$) in six X-ray binaries (XRBs) with well constrained black hole masses and distances. We find that…
We present results from a Chandra study of ultraluminous X-ray sources (ULXs) in a sample of 17 nearby (D_L<60 Mpc) luminous infrared galaxies (LIRGs), selected to have star formation rates (SFRs) in excess of 7 M_sun yr^-1 and low…
Two recent observations of the nearby galaxy NGC 6946 with NuSTAR, one simultaneous with an XMM-Newton observation, provide an opportunity to examine its population of bright accreting sources from a broadband perspective. We study the…
We investigate the X-ray spectrum, variability and the surrounding ionized bubble of NGC1313 X-2 to explore the physics of super-Eddington accretion. Beyond the Eddington luminosity, the accretion disk of NGC1313 X-2 is truncated at a large…
Most ultraluminous X-ray sources (ULXs) are thought to be supercritical accreting compact objects, where massive outflows are inevitable. Using the long-term monitoring data with the Swift X-ray Telescope, we identified a common feature in…
Luminosities of ultraluminous X-ray sources (ULXs) are uncomfortably large if compared to the Eddington limit for isotropic accretion onto stellar-mass object. Most often either supercritical accretion onto stellar mass black hole or…
Ultraluminous X-ray sources (ULXs) are X-ray binary systems containing an accreting neutron star (NS) or black hole emitting at luminosities above the Eddington limit of a $10M_{\odot}$ black hole. Approximately 1900 (either confirmed or…
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…
Ultra-luminous Compact X-ray Sources (ULXs) in nearby spiral galaxies and Galactic superluminal jet sources share the common spectral characteristic that they have unusually high disk temperatures which cannot be explained in the framework…
Although attempts have been made to constrain the stellar types of optical counterparts to ULXs, the detection of optical variability instead suggests that they may be dominated by reprocessed emission from X-rays which irradiate the outer…
It has recently been discovered that a fraction of ultra-luminous X-ray sources (ULXs) exhibit X-ray pulsations, and are therefore powered by super-Eddington accretion onto magnetized neutron stars (NSs). For typical ULX mass accretion…
We present a comprehensive spectro-temporal analysis of five ultraluminous X-ray sources (ULXs) with central object likely being a black hole, using archival {\it XMM-Newton} observations. These sources, namely NGC 1313 X-1, NGC 5408 X-1,…
We present a multi-mission X-ray analysis of a bright (peak observed 0.3-10 keV luminosity of ~ 6x10^{40} erg s^{-1}), but relatively highly absorbed ULX in the edge-on spiral galaxy NGC 5907. The ULX is spectrally hard in X-rays (Gamma ~…
Ultra-luminous X-ray sources (ULXs) are off-nuclear point sources in nearby galaxies with luminosities well exceeding the Eddington limit for stellar-mass objects. It has been recognized after the discovery of pulsating ULXs (PULXs) that a…
The closest known ultraluminous X-ray source (ULX), M33 X-8, has been recently observed with NuSTAR during its Extragalactic Legacy program, which includes a hard X-ray survey of the M33 galaxy. We present results of two long observations…