Related papers: X-ray Outflows and Super-Eddington Accretion in th…
We present results obtained from two broadband X-ray observations of the extreme ultraluminous X-ray source (ULX) NGC5907 ULX1, known to have a peak X-ray luminosity of ~5e40 erg/s. These XMM-Newton and NuSTAR observations, separated by…
We have studied a highly variable ultraluminous X-ray source (ULX) in the Fornax galaxy NGC 1365, with a series of 12 Chandra and XMM-Newton observations between 2002 and 2006. In 2006 April, the source peaked at a luminosity ~ 3 x 10^{40}…
An optically thin advective accretion disk is crucial for explaining the hard state of black hole sources. Using general relativistic magnetohydrodynamic (GRMHD) simulations, we investigate how a large-scale, strong magnetic field…
The hyper luminous X-ray source HLX-1 in the galaxy ESO 243-49, currently the best intermediate mass black hole candidate, displays spectral transitions similar to those observed in Galactic black hole binaries, but with a luminosity…
We present nearly simultaneous NuSTAR and XMM-Newton observations of the nearby (832 kpc) ultraluminous X-ray source (ULX) M33 X-8. M33 X-8 has a 0.3-10 keV luminosity of LX ~ 1.4 x 10^39 erg/s, near the boundary of the "ultraluminous"…
The classical limit on the accretion luminosity of a neutron star is given by the Eddington luminosity. The advanced models of accretion onto magnetized neutron stars account for the appearance of magnetically confined accretion columns and…
We perform radiative magnetohydrodynamics simulations in general relativity (GRRMHD) of super-Eddington disk accretion onto neutron stars endowed with a magnetic dipole corresponding to surface strengths not exceeding 100 GigaGauss.…
With the discovery of pulsations in some of the ultra-luminous X-ray sources (ULXs), it is quite clear that most of the ULXs harbor either a neutron star or a stellar mass black hole as a compact object accreting at super-Eddington rates.…
We use XMM-Newton and Swift data to study spectral variability in the ultraluminous X-ray source (ULX), Holmberg IX X-1. The source luminosity varies by a factor 3-4, giving rise to corresponding spectral changes which are significant, but…
Despite much observational and theoretical effort little is presently known about the nature of the luminous non-nuclear X-ray sources which appear to largely surpass the Eddington limit of a few solar masses. Here we present first results…
We report the discovery of a new candidate ultraluminous X-ray source (ULX) in the nearby edge-on spiral galaxy NGC 891. The source, which has an absorbed flux of F_X ~ 10^-12 erg/s/cm^2 (corresponding to L_X > 10^40 erg/s at 9 Mpc), must…
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…
We report the discovery of a new ultraluminous X-ray source (ULX) associated with a globular cluster in the elliptical galaxy NGC 4649. The X-ray source was initially detected with a luminosity below 5 x 10^38 erg/s, but in subsequent…
Ultra-luminous X-ray sources (ULXs) are sources observed to exceed the Eddington limit of a stellar-mass black hole (BH). A fraction of ULX sources show X-ray pulses which are evidence for accreting neutron stars (NSs). Theoretical studies…
Ultraluminous X-ray Sources (ULXs) provide a unique opportunities to probe the geometry and energetics of super-Eddington accretion. The radiative processes involved in super-Eddington accretion are not well understood, and so studying…
X-ray observations have revealed in other galaxies a class of extra-nuclear X-ray point sources with X-ray luminosities of $10^{39}$--$10^{41}$ erg/sec, exceeding the Eddington luminosity for stellar mass X-ray binaries. These…
An XMM-Newton study of ultraluminous X-ray sources (ULX) has been performed in a sample of 10 nearby Seyfert galaxies. Eighteen ULX have been found with positional uncertainty of about 4". The large collecting area of XMM-Newton makes the…
The black hole mass and accretion rate in Ultraluminous X-ray sources (ULXs) in external galaxies, whose X-ray luminosities exceed those of the brightest black holes in our Galaxy by hundreds and thousands of times$^{1,2}$, is an unsolved…
Variability is a powerful tool to investigate properties of X-ray binaries (XRB), in particular for Ultraluminous X-ray sources (ULXs) that are mainly detected in the X-ray band. For most ULXs the nature of the accretor is unknown, although…
Ultraluminous X-ray sources (ULXs) represent a class of binary systems that are more luminous than any black hole in our Galaxy. The nature of these objects remained unclear for a long time. The most popular models for the ULXs involve…