Related papers: Spectral evolution of the ultraluminous X-ray sour…
M82 X-1 is one of the brightest ultraluminous X-ray sources (ULXs) known, which, assuming Eddington-limited accretion and other considerations, makes it one of the best intermediate-mass black hole (IMBH) candidates. However, the ULX may…
Ultra-luminous X-ray sources (ULXs) are a class of extra-galactic, point-like, off-nuclear X-ray sources with X-ray luminosity from $\sim 10^{39}$~erg s$^{-1}$ to $10^{41}$~erg s$^{-1}$. We investigated the temporal and broadband X-ray…
We present results for two Ultraluminous X-ray Sources (ULXs), IC 342 X-1 and IC 342 X-2, using two epochs of XMM-Newton and NuSTAR observations separated by $\sim$7 days. We observe little spectral or flux variability above 1 keV between…
We present the results of NuSTAR and XMM-Newton observations of the two ultraluminous X-ray sources (ULX) NGC 1313 X-1 and X-2. The combined spectral bandpass of the two satellites enables us to produce the first spectrum of X-1 between 0.3…
We present results from the coordinated broadband X-ray observations of the extreme ultraluminous X-ray source Holmberg IX X-1 performed by NuSTAR, XMM-Newton and Suzaku in late 2012. These observations provide the first high-quality…
We present the first broadband 0.3-25.0 kev X-ray observations of the bright ultraluminous X-ray source (ULX) Holmberg II X-1, performed by NuSTAR, XMM-Newton and Suzaku in September 2013. The NuSTAR data provide the first observations of…
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 examined spectral evolution in ultraluminous X-ray sources (ULXs) with apparent luminosities of about 10^40 ergs/s. Based on new results in this paper and those reported in the literature, two common spectral behaviors were found. Some…
The study of quasi-periodic oscillations in X-ray binaries provides valuable insights into the physics of accretion around compact objects. The M82 galaxy hosts two ultraluminous X-ray sources (ULXs), one of which is suspected to harbor an…
The discovery of pulsations in several Ultraluminous X-ray sources (ULXs) demonstrated that a fraction of ULXs are powered by super-Eddington accretion onto neutron stars (NSs). This opened the debate as to what is the NS to black hole (BH)…
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"…
We present the results of the first broadband X-ray analysis of the ultraluminous X-ray source NGC 5055 ULX X-1, combining simultaneous data from XMM$-$Newton and NuSTAR missions, with a combined exposure time of $\sim$100 ks across the…
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…
Emission spectra of hot accretion disks characteristic of advection dominated accretion flow (ADAF) models are investigated for comparison with the brightest ultra-luminous source, X-1, in the galaxy M82. If the spectral state of the source…
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…
We observed the nearby and relatively understudied ultraluminous X-ray source (ULX) NGC 4190 ULX-1 jointly with NICER and NuSTAR to investigate its broadband spectrum, timing properties, and spectral variation over time. We found NGC 4190…
We present a new analysis of X-ray spectra of the archetypal ultraluminous X-ray source (ULX) Holmberg IX X-1 obtained by the Swift, XMM-Newton and NuSTAR observatories. This ULX is a persistent source, with a typical luminosity of ~10^40…
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…
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…
The recent discovery by Bachetti et al. (2014) of a pulsar in M82 that can reach luminosities of up to 10^40 ergs s^-1, a factor of ~100 the Eddington luminosity for a 1.4 Msol compact object, poses a challenge for accretion physics. In…