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We present the XMM-Newton discovery of X-ray emission from the planetary nebula (PN) A78, the second born-again PN detected in X-rays apart from A30. These two PNe share similar spectral and morphological characteristics: they harbor diffuse soft X-ray emission associated with the interaction between the H-poor ejecta and the current fast stellar wind and a point-like source at the position of the central star (CSPN). We present the spectral analysis of the CSPN, using for the first time an NLTE code for expanding atmospheres that takes line blanketing into account for the UV and optical spectra. The wind abundances are used for the X-ray spectral analysis of the CSPN and the diffuse emission. The X-ray emission from the CSPN in A78 can be modeled by a single C VI emission line, while the X-ray emission from its diffuse component is better described by an optically thin plasma emission model with a temperature of kT = 0.088 keV (T approximate to 1.0 x 10(6) K). We estimate X-ray luminosities in the 0.2-2.0 keV energy band of L-X,L-CSPN =(1.2 +/- 0.3) x 10(31) erg s(-1) and L-X,L-DIFF =(9.2 +/- 2.3) x 10(30) erg s(-1) for the CSPN and diffuse components, respectively.
We present a comprehensive analysis of the whole sample of available XMM-Newton observations of high-mass X-ray binaries (HMXBs) until August 2013, focusing on the FeK alpha emission line. This line is key to better understanding the physical properties of the material surrounding the X-ray source within a few stellar radii (the circumstellar medium). We collected observations from 46 HMXBs and detected FeK alpha in 21 of them. We used the standard classification of HMXBs to divide the sample into different groups. We find that (1) different classes of HMXBs display different qualitative behaviours in the FeK alpha spectral region. This is visible especially in SGXBs (showing ubiquitous Fe fluorescence but not recombination Fe lines) and in gamma Cass analogues (showing both fluorescent and recombination Fe lines). (2) FeK alpha is centred at a mean value of 6.42 keV. Considering the instrumental and fits uncertainties, this value is compatible with ionization states that are lower than Fe xviii. (3) The flux of the continuum is well correlated with the flux of the line, as expected. Eclipse observations show that the Fe fluorescence emission comes from an extended region surrounding the X-ray source. (4) We observe an inverse correlation between the X-ray luminosity and the equivalent width of FeK alpha (EW). This phenomenon is known as the X-ray Baldwin effect. (5) FeK alpha is narrow (sigma(line) < 0.15 keV), reflecting that the reprocessing material does not move at high speeds. We attempt to explain the broadness of the line in terms of three possible broadening phenomena: line blending, Compton scattering, and Doppler shifts (with velocities of the reprocessing material V similar to 1000 km s(-1)). (6) The equivalent hydrogen column (N-H) directly correlates to the EW of FeK alpha, displaying clear similarities to numerical simulations. It highlights the strong link between the absorbing and the fluorescent matter. (7) The observed NH in supergiant X-ray binaries (SGXBs) is in general higher than in supergiant fast X-ray transients (SFXTs). We suggest two possible explanations: different orbital configurations or a different interaction compact object - wind. (8) Finally, we analysed the sources IGR J16320-4751 and 4U 1700-37 in more detail, covering several orbital phases. The observed variation in NH between phases is compatible with the absorption produced by the wind of their optical companions. The results clearly point to a very important contribution of the donor's wind in the FeK alpha emission and the absorption when the donor is a supergiant massive star.
We present an analysis of a 78 ks Chandra high-energy transmission gratings observation of the B0I star QV Nor, the massive donor of the wind-accreting pulsar 4U1538-52. The neutron star (NS) orbits its companion in a very close orbit (r < 1.4R(*), in units of the stellar radii), thereby allowing probing of the innermost wind regions. The flux of the Fe K alpha line during eclipse reduces to only similar to 30% of the flux measured out of eclipse. This indicates that the majority of Fe fluorescence must be produced in regions close to the NS, at distances smaller than 1R(*) from its surface. The fact that the flux of the continuum decreases to only similar to 3% during eclipse allows for a high contrast of the Fe Ka line fluorescence during eclipse. The line is not resolved and centered at lambda = 1.9368(-0.0018)(+0.0032) angstrom. From the inferred plasma speed limit of v < c Delta lambda/lambda < 800 km s(-1) and range of ionization parameters of log xi =[-1, 2], together with the stellar density profile, we constrain the location of the cold, dense material in the stellar wind of QV Nor using simple geometrical considerations. We then use the Fe K alpha line fluorescence as a tracer of wind clumps and determine that these clumps in the stellar wind of QV Nor (B0I) must already be present at radii r < 1.25R(*), close to the photosphere of the star.