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We have analysed data from five XMM-Newton observations of XB 1254-690, one of them simultaneous with INTEGRAL, to investigate the mechanism responsible for the highly variable dip durations and depths seen from this low-mass X-ray binary. Deep dips were present during two observations, shallow dips during one and no dips were detected during the remaining two observations. At high (1–4 s) time resolution “shallow dips” are seen to include a few very rapid, deep dips whilst the “deep” dips consist of many similar very rapid, deep fluctuations. The folded V-band Optical Monitor light curves obtained when the source was undergoing deep, shallow and no detectable dipping exhibit sinusoid-like variations with different amplitudes and phases. We fit EPIC spectra obtained from “persistent” or dip-free intervals with a model consisting of disc-blackbody and thermal Comptonisation components together with Gaussian emission features at 1 and 6.6 keV modified by absorption due to cold and photo-ionised material. None of the spectral parameters appears to be strongly correlated with the dip depth except for the temperature of the disc blackbody which is coolest (kT~ 1.8 keV) when deep dips are present and warmest (kT~ 2.1 keV) when no dips are detectable. We propose that the changes in both disc temperature and optical modulation could be explained by the presence of a tilted accretion disc in the system. We provide a revised estimate of the orbital period of 0.16388875 ±0.00000017 day.

We report on two simultaneous XMM-Newton and INTEGRAL observations of the microquasar GRO J1655-40during the 2005 outburst when the source was in its high-soft state. The 0.3–200 keV spectra are complex with an overall continuum which may be modeled using an absorbed blackbody together with a weak, steep, power-law component. In addition, there is evidence for the presence of botha relativistically broadened Fe K line and a highly photo-ionized absorber. The photo-ionized absorber is responsible for strong K absorption lines of $\ion{Fe}{xxv}$and $\ion{Fe}{xxvi}$in the EPIC pn spectra and blue-shifted ($v = -540$±120 km s-1) $\ion{Ne}{x}$and $\ion{Fe}{xxiv}$features in the RGS spectra. The parameters of the photo-ionized absorber were different during the two observations with the ionization parameter, $\log(\xi)$, decreasing from 3.60 ±0.04 to 3.30 ±0.04 erg cm s-1and the column density decreasing from $(5.2 \pm 1.0)$$\times~$1022atom cm-2to $(1.5 \pm 1.0)$$\times~$1022atom cm-2during the first and second observations as the 0.5–200 keV GRO J1655-40 luminosity decreased by around a half. At 90% confidence the INTEGRAL data show no evidence of a break in the power-law component up to energies of 380 keV and 90 keV for the first and second observations, respectively.

X-ray observations have revealed that many microquasars and low-mass X-ray binaries (LMXBs) exhibit narrow absorption features identified with resonant absorption from $\ion{Fe}{xxv}$and $\ion{Fe}{xxvi}$and other abundant ions. In many well studied systems there is evidence for blue-shifts, indicating outflowing plasmas. We succesfully model the changes in boththe X-ray continuum and the Fe absorption features during dips from all the bright dipping LMXBs observed by XMM-Newton (EXO 0748-676, XB 1254-690, X 1624-490, MXB 1659-298, 4U 1746-371 and XB 1916-053) as resulting primarily from an increase in column density and a decrease in the ionization state of a highly-ionized absorber in a similar way as was done for XB 1323-619. This implies that the complex spectral changes in the X-ray continua observed from the dip sources as a class can be most simply explained primarily by changes in the highly ionized absorbers present in these systems. There is no need to invoke unusual abundances or partial covering of extended emission regions. Outside of the dips, the absorption line properties do not vary strongly with orbital phase. This implies that the ionized plasma has a cylindrical geometry with a maximum column density close to the plane of the accretion disk. Since dipping sources are simply normal LMXBs viewed from close to the orbital plane this implies that ionized plasmas are a common feature of LMXBs.

The neutron star low-mass X-ray binary EXO 0748−676 started a transition from outburst to quiescence in August 2008, after more than 24 years of continuous accretion. The return of the source to quiescence has been monitored extensively by several X-ray observatories. Here, we report on four XMM-Newtonobservations elapsing a period of more than 19 months that started in November 2008. The X-ray spectra contain a soft thermal component that we fit with a neutron-star atmosphere model. In only the first observation do we find a significant second component above  ~3 keV accounting for  ~7% of the total flux, which might be indicative of residual accretion. The thermal bolometric flux and the temperature of the neutron star crust decrease steadily by 40% and 10%, respectively, between the first and the fourth observations. At the time of the last observation in June 2010, we obtain a thermal bolometric luminosity of 5.6  ×  1033(d/7.1 kpc)2erg s-1and a temperature of the neutron star crust of 109 eV. The cooling curve is consistent with a relatively hot medium-mass neutron star cooling by standard mechanisms. From the spectral fits to a neutron-star atmosphere model, we infer limits to the mass and the radius of the neutron star. We find that to achieve self-consistency between the neutron-star masses derived using the different methods, the value of the distance is constrained to be  ≲6 kpc. For this value of the distance, the derived mass and radius contours are consistent with a number of EoSs with nucleons and hyperons.

We analysed the XMM-Newtonarchival observations of 16 neutron star (NS), low-mass X-ray binaries (LMXBs) to study the Fe K emission in these objects. The sample includes all the observations of NS LMXBs performed in EPIC pn timing mode with XMM-Newtonpublicly available until September 30, 2009. We performed a detailed data analysis considering pile-up and background effects. The properties of the Fe lines differed from previous published analyses because of either incorrect pile-up corrections or different continuum parameterisation. Eighty percent of the observations for which a spectrum can be extracted showed significant Fe line emission. We found an average line centroid of 6.67  ±  0.02 keV and a finite width, σ, of 0.33  ±  0.02 keV. The equivalent width of the lines varied between 17 and 189 eV, with an average weighted value of 42  ±  3 eV. For sources where several observations were available, the Fe line parameters changed between observations whenever the continuum changed significantly. The line parameters did not show any correlation with luminosity. Most important, we could fit the Fe line with a simple Gaussian component for all the sources. The lines did not show the asymmetric profiles that were interpreted as indicating relativistic effects in previous analyses of these LMXBs.