Related papers: A variable ULX and possible IMBH candidate in M51a

The luminosity range at and just below the 10^39 erg/s cut-off for defining ultraluminous X-ray sources (ULXs) is a little-explored regime. It none-the-less hosts a large number of X-ray sources, and has great potential for improving our…

The small subset of hyper-luminous X-ray sources with luminosities in excess of ~1E41 erg/s are hard to explain without the presence of an intermediate mass black hole, as significantly super-Eddington accretion and/or very small beaming…

We report the results of Chandra and XMM-Newton observations of a new outburst of an ultraluminous supersoft X-ray source in M101. CXOU J140332.3+542103 was observed in a low luminosity state (L_x~1e37 erg/s) between 2004 January and May.…

We studied the colliding galaxy NGC 7714 with two XMM-Newton observations, six months apart. The galaxy contains two bright X-ray sources: we show that they have different physical nature. The off-nuclear source is an accreting compact…

We report on six Chandra and one HST/WFC3 observation of CXO J122518.6+144545, discovered by Jonker et al. (2010) as a candidate hyperluminous X-ray source (HLX), X-ray bright supernova or recoiling supermassive black hole at $L_X = 2.2…

We present the results of a temporal and spectral analysis of the transient source ULX-4 in the galaxy M51. The data used were drawn from Chandra, XMM-Newton and Swift-XRT archives, spanning the years 2000-2019. The X-ray flux of the source…

Ultraluminous X-ray sources (ULXs) are amongst the most intriguing of X-ray source classes. Their extreme luminosities - greater than 10^39 erg/s in the 0.3 - 10 keV band alone - suggest either the presence of black holes larger than those…

We report the first clear evidence for the simultaneous presence of a low frequency break and a QPO in the fluctuation power spectrum of a well known ultraluminous X-ray source (ULX) in M82 using long XMM-Newton observations. The break…

Here we present the results of panoramic and long-slit observations of eight ULX nebular counterparts held with the 6m SAO telescope. In two ULXNe we detected for the first time signatures of high excitation ([OIII]5007 / H\beta > 5). Two…

Some ultraluminous X-ray sources (ULXs) exhibit X-ray pulses, and their central sources are thought to be neutron stars. It has also been suggested that some are transient sources with Be-type donors. In this study, we use the mass…

Chandra observations of 17 nearby galaxies were analysed and 166 bright sources with X-ray counts > 100, were chosen for temporal analysis. Fractional root mean square variability amplitudes were estimated for lightcurves binned at ~ 4 ksec…

We show with a short Chandra HRC-S exposure that the powerful X-ray source coincident with the nucleus of M33 is unresolved at the highest spatial resolution available to date (0"4). The source flux is variable, doubling during the 5 ks…

Ultraluminous X-ray sources (ULXs) with Lx > 10^{39} ergs/s have been discovered in great numbers in external galaxies with ROSAT, Chandra, and XMM. The central question regarding this important class of sources is whether they represent an…

The ultraluminous X-ray source (ULX), NGC 5408 X-1, is one of only 3 such objects to show a quasi-periodic oscillation (QPO) in its power spectrum. Previous analysis of this signal identified it with the well-studied type C low-frequency…

The extreme extragalactic sources known as Ultraluminous X-ray Sources (ULX) represent a unique testing environment for compact objects population studies and the accretion process. Their nature has long been disputed. Their luminosity,…

All 63 discrete X-ray sources brighter than L_{\rm X} = 5x10^{36} erg/s in any of four XMM-Newton observations of the core of M31 were surveyed for time variability over time-scales of seconds to thousands of seconds, and for intensity…

We examine the X-ray spectra and variability of the sample of X-ray sources with L_X = 10^{31}-10^{33} erg s^{-1} identified within the inner 9' of the Galaxy. Very few of the sources exhibit intra-day or inter-month variations. We find…

Ultraluminous X-ray sources (ULXs) are mostly extragalactic non-nuclear point sources having X-ray luminosity exceeding the Eddington luminosity of 10 $M_\odot$ black hole i.e., $L_X \geq $ 10$^{39}$ erg ~s$^{-1}$. They are observed in all…

We present the discovery and interpretation of ionized nebulae around two ultraluminous X-ray sources in M 51; both sources share the rare property of showing X-ray eclipses by their companion stars, and are therefore prime targets for…

Ultraluminous X-ray sources (ULXs) with 10^39 < L_x < 10^41 erg/s have been discovered in great numbers in external galaxies with ROSAT, Chandra, and XMM-Newton. The central question regarding this important class of sources is whether they…