Related papers: A Wolf-Rayet/black-hole X-ray binary candidate in …

We obtained multi-epoch Very Large Telescope (VLT) optical spectroscopic data in 2011 and 2012 on the ultraluminous X-ray source (ULX) NGC 5408 X-1. We confirm that the HeII\lambda4686 line has a broad component with an average FWHM of…

We report the discovery of an X-ray source coincident with the nuclear star cluster at the dynamical center of the nearby late-type spiral galaxy NGC 2403. The X-ray luminosity of this source varies from below detection levels, ~1e35 erg/s…

The ultra-luminous X-ray (ULX) source ESO 243-49 HLX-1 currently provides the strongest evidence for the existence of intermediate mass black holes. We conduct an ongoing monitoring campaign with the Swift X-ray Telescope and found that…

The Cartwheel is one of the most outstanding examples of a dynamically perturbed galaxy where star formation is occurring inside the ring--like structure. In previous studies with Chandra, we detected 16 Ultra Luminous X-ray sources lying…

NGC 925 ULX-1 and ULX-2 are two ultraluminous X-ray sources in the galaxy NGC 925, at a distance of 8.5 Mpc. For the first time, we analyzed high quality, simultaneous XMM-Newton and NuSTAR data of both sources. Although at a first glance…

The nature of ultra-luminous X-ray sources (ULXs) has long been plagued by an ambiguity about whether the central compact objects are intermediate-mass (IMBH, >~ 10^3 M_sun) or stellar-mass (a few tens M_sun) black holes (BHs). The high…

Four XMM-Newton observations of the core of M31, spaced at 6 month intervals, show that the brightest point X-ray source, RX J0042.6+4115, has a 0.4-10 keV luminosity of ~5 10^38 erg/s, and exhibits significant variability in intensity and…

This paper reports the search for quiescent low-mass X-ray binaries (qLMXBs) in the globular cluster (GC) NGC 6553 using an XMM-Newton observation designed specifically for that purpose. We spectrally identify one candidate qLMXB in the…

We present the first results of an XMM-Newton EPIC observation of the luminous X-ray source population in the supergiant spiral galaxy M101. We have studied the properties of the fourteen most luminous sources, all of which have intrinsic…

We investigate the nature of CXOU J005440.5-374320 (J0054), a peculiar bright ($\sim$$4\times10^{39}$ erg/s) and soft X-ray transient in the spiral galaxy NGC 300 with a 6-hour periodic flux modulation that was detected in a 2014 Chandra…

Narrow, highly ionized X-ray emission lines in black hole low-mass X-ray binaries (BH-LMXBs) are rare and have been observed in only a few sources, during unusual, heavily obscured accretion states. We report on a detailed high-resolution…

We report the results of a deep Chandra survey of the Sculptor dwarf spheroidal galaxy. We find five X-ray sources with $L_X$ of at least $6\times10^{33}$ ergs/sec with optical counterparts establishing them as members of Sculptor. These…

We present the first result of a programme to search for large flux variations in the X-ray sources of the XMM Serendipitous Survey compared to previous ROSAT observations. An increase in X-ray flux by a factor >10 was discovered from the…

In an XMM-Newton raster observation of the bright Local Group spiral galaxy M 33 we study the population of X-ray sources (X-ray binaries, supernova remnants) down to a 0.2--4.5 keV luminosity of 10^35 erg/s -- more than a factor of 10…

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…

Ultraluminous and hyperluminous X-ray sources (ULXs and HLXs) are among the brightest astrophysical objects in the X-ray sky. While ULXs most likely host stellar-mass compact objects accreting at super-Eddington rates, HLXs are compelling…

Stochastic variability in two out of four XMM-Newton observations of XMMU J004303+4115 along with its power spectra and X-ray luminosities suggest a low-mass X-ray binary (LMXB) with a black hole primary. However, Chandra observations…

X-ray point sources in galaxies are dominated by X-ray binaries (XRBs) that are variables or transients and whether their variability would alter the X-ray luminosity functions (XLF) is still in debate. Here we report on NGC 7331 as an…

The majority of the ultraluminous X-ray sources (ULXs) in external galaxies are believed to be accreting black holes in binary systems; some of the black holes could be as massive as $\sim 100-1000 \ms$. We have performed evolution…

We present a detailed analysis of XMM archival data of two Ultraluminous X-ray Sources (ULXs) in the nearby spiral galaxy NGC 1313: NGC 1313 X-1 and X-2. The spectral continuum of these sources was modeled with a soft thermal component plus…