We studied the low‐frequency quasi‐periodic oscillations (LFQPOs) in the black hole GRO J1655−40 during the 2005 outburst, using data from the Rossi X‐ray Timing Explorer. All LFQPOs could be identified as either type B or type C using previously proposed classification schemes. In the soft state of the outburst the type‐C LFQPOs reached frequencies that are among the highest ever seen for LFQPOs in black holes. At the peak of the outburst, in the ultraluminous state, the power spectrum showed two simultaneous, non‐harmonically related peaks which we identified as a type‐B and a type‐C QPO. The simultaneous presence of a type‐C and type‐B QPO shows that at least two of the three known LFQPO types are intrinsically different and likely the result of distinct physical mechanisms. We also studied the properties of a broad peaked noise component in the power spectra of the ultraluminous state. This noise component becomes more coherent with count rate and there are strong suggestions that it evolves into a type‐B QPO at the highest observed count rates.

We analysed the X-ray spectra of six observations, simultaneously taken with XMMNewton and Rossi X-ray Timing Explorer (RXTE), of the neutron star low-mass X-ray binary 4U 1636-53. The observations cover several states of the source, and therefore a large range of inferred mass accretion rate. These six observations show a broad emission line in the spectrum at around 6.5 keV, likely due to iron. We fitted this line with a set of phenomenological models of a relativistically broadened line, plus a model that accounts for relativistically smeared and ionised reflection from the accretion disc. The latter model includes the incident emission from both the neutronstar surface or boundary layer and the corona that is responsible for the high-energy emission in these systems. From the fits with the reflection model we found that in four out of the six observations the main contribution to the reflected spectrum comes from the neutron-star surface or boundary layer, whereas in the other two observations the main contribution to the reflected spectrum comes from the corona. We found that the relative contribution of these two components is not correlated to the state of the source. From the phenomenological models we found that the iron line profile is better described by a symmetric, albeit broad, profile. The width of the line cannot be explained only by Compton broadening, and we therefore explored the case of relativistic broadening. We further found that the direct emission from the disc, boundary layer, and corona generally evolved in a manner consistent with the standard accretion disc model, with the disc and boundary layer becoming hotter and the disc moving inwards as the source changed from the hard in to the soft state. The iron line, however, did not appear to follow the same trend.

We observed the new X-ray transient and black hole candidate XTE J1652−453 simultaneously with XMM-Newton and the Rossi X-ray Timing Explorer (RXTE). The observation was done during the decay of the 2009 outburst, when XTE J1652−453 was in the hard-intermediate state. The spectrum shows a strong and broad Fe emission line with an equivalent width of ∼450 eV. The profile is consistent with that of a line being produced by reflection off the accretion disc, broadened by relativistic effects close to the black hole. The best-fitting inner radius of the accretion disc is ∼4 gravitational radii. Assuming that the accretion disc is truncated at the radius of the innermost stable circular orbit, the black hole in XTE J1652−453 has a spin parameter of ∼0.5. The power spectrum of the RXTE observation has an additional variability component above 50 Hz, which is typical for the hard-intermediate state. No coherent quasiperiodic oscillations at low frequency are apparent in the power spectrum, which may imply that we view the system at a rather low inclination angle.

We analyzed simultaneous archival XMM-Newton and RXTE observations of the Xray binary and black hole candidate Swift J1753.5−0127. In a previous analysis of the same data a soft thermal component was found in the X-ray spectrum, and the presence of an accretion disk extending close to the innermost stable circular orbit was proposed. This is in contrast with the standard picture in which the accretion disk is truncated at large radii in the low/hard state. We tested a number of spectral models and we found that several of them fit the observed spectra without the need of a soft disk-like component. This result implies that the classical paradigm of a truncated accretion disk in the low/hard state can not be ruled out by these data. We further discovered a broad iron emission line between 6 and 7 keV in these data. From fits to the line profile we found an inner disk radius that ranges between ∼6-16 gravitational radii, which can be in fact much larger, up to ∼250 gravitational radii, depending on the model used to fit the continuum and the line. We discuss the implications of these results in the context of a fully or partially truncated accretion disk.

We used six simultaneous XMM-Newton and Rossi X-ray Timing Explorer plus five Suzaku observations to study the continuum spectrum and the iron emission line in the neutron-star low-mass X-ray binary 4U 1636−53. We modelled the spectra with two thermal components (representing the accretion disc and boundary layer), a Comptonised component (representing a hot corona), and either a Gaussian or a relativistic line component to model an iron emission line at ∼ 6.5 keV. For the relativistic line component we used either the diskline, laor or kyrline model, the latter for three different values of the spin parameter. The fitting results for the continuum are consistent with the standard truncated disc scenario. We also find that the flux and equivalent width of the iron line first increase and then decrease as the flux of the Comptonised component increases. This could be explained either by changes in the ionisation state of the accretion disc where the line is produced by reflection, or by light bending of the emission from the Comptonised component if the height at which this component is produced changes with mass accretion rate.