Related papers: The Eclipsing ULX in NGC 3379

We report on the first near-simultaneous X-ray and optical observations of RX J0806.3+1527. The source is believed to be a 321s orbital period ultra-compact binary system hosting an X-ray emitting white dwarf. Data were obtained with…

NGC 55 ULX1 is a bright Ultraluminous X-ray source located 1.78 Mpc away. We analysed a sample of 20 Swift observations, taken between 2013 April and August, and two Chandra observations taken in 2001 September and 2004 June. We found only…

The X-ray source RX J0648.0-4418 is the only confirmed binary system in which a compact object, most likely a massive white dwarf, accretes from a hot subdwarf companion, the bright sdO star HD 49798. The X-ray emission from this system is…

Ultra-luminous X-ray sources (ULX) have so high X-ray luminosities that they were long thought to be accreting intermediate mass black holes. Yet, some ULX have been shown to display periodic modulations and coherent pulsations, suggestive…

Ultraluminous pulsars are a definite proof that persistent super-Eddington accretion occurs in nature. They support the scenario according to which most Ultraluminous X-ray Sources (ULXs) are super-Eddington accretors of stellar mass rather…

The source X 1822-371 is an eclipsing compact binary system with a period close to 5.57 hr and an orbital period derivative $\dot{P}_{\rm orb}$ of 1.51(7)$\times 10^{-10}$ s s$^{-1}$. The very large value of $\dot{P}_{\rm orb}$ is…

NGC 3227 exhibits rapid flux and spectral variability in the X-ray band. To understand this behaviour we conducted a co-ordinated observing campaign using 320 ks of XMM-Newton exposures together with 160 ks of overlapping NuSTAR…

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 report the detection of weak pulsations from the archetypal ultraluminous X-ray source (ULX) NGC 1313 X-2. Acceleration searches reveal sinusoidal pulsations in segments of two out of six new deep observations of this object, with a…

We studied the radio source associated with the ultraluminous X-ray source in NGC 5408 (L_X ~ 10^{40} erg/s). The radio spectrum is steep (index ~ -1), consistent with optically-thin synchrotron emission, not with flat-spectrum core…

Obscuration of the continuum emission from active galactic nuclei by streams of gas with relatively high velocity (> 1000 km/s) and column density (>3E25 per m2) has been seen in a few Seyfert galaxies. This obscuration has a transient…

Recent observations of galaxies continue to reveal new ultraluminous X-ray sources (ULXs), increasing their known population and improving the statistics needed to understand their nature. We study the ULX populations of NGC 4631 and NGC…

(Abridged) Stellar mass black hole X-ray binaries exhibit X-ray spectral states which also have distinct and characteristic temporal properties. These states are believed to correspond to different accretion disk geometries. We present…

We have identified the optical counterpart of the ULX source P13 in the nearby spiral galaxy NGC 7793. The object is a V ~ 20.5 mag star, ten times brighter than any other established counterpart of a ULX in nearby galaxies. Medium…

With Very Large Telescope (VLT) Multi Unit Spectroscopic Explorer (MUSE) observations, we detected highly variable helium emission lines from the optical counterpart of the supersoft ultraluminous X-ray source (ULX) NGC 247 ULX-1. No Balmer…

We report the spectral and temporal variability properties of 18 candidate transient and potential transient (TC and PTC) sources detected in deep multi-epoch Chandra observation of the nearby elliptical galaxies, NGC 3379, NGC 4278 and NGC…

Several dozen binary ultracool and brown dwarf systems have been identified to date. These systems represent valuable probes of star and planet formation at the lowest mass scales. To date, the study of these ultracool binaries has been…

The luminous low-mass X-ray binary X2127+119 in the core of the globular cluster M15 (NGC 7078), which has an orbital period of 17 hours, has long been assumed to contain a donor star evolving off the main sequence, with a mass of 0.8 solar…

In this proof-of-concept study we demonstrate that in a binary system mass can be transferred toward an accreting compact object at extremely high rate. If the transferred mass is efficiently converted to X-ray luminosity (with disregard of…

We present an analysis of the ultraluminous X-ray source (ULX) population in 75 Virgo cluster late-type galaxies, including all those with a star formation rate >~ 1 M_{sun}/yr and a representative sample of the less star-forming ones. This…