131 research outputs found

    Disc atmospheres and winds in X-ray binaries

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    We review the current status of studies of disc atmospheres and winds in low mass X-ray binaries. We discuss the possible wind launching mechanisms and compare the predictions of the models with the existent observations. We conclude that a combination of thermal and radiative pressure (the latter being relevant at high luminosities) can explain the current observations of atmospheres and winds in both neutron star and black hole binaries. Moreover, these winds and atmospheres could contribute significantly to the broad iron emission line observed in these systems.Comment: Accepted for publication in Acta Polytechnica. Invited review talk at the Vulcano Workshop 2012: "Frontier Objects in Astrophysics and Particle Physics

    On the Low and High Frequency Correlation in Quasi-Periodic Oscillations Among White Dwarfs, Neutron Star and Black Hole Binaries

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    We interpret the correlation over five orders of magnitude between high frequency and low frequency in a quasi-periodic oscillations (QPO) found by Psaltis, Belloni & van der Klis (1999) for black hole (BH), neutron star (NS) systems and then extended by Mauche (2002) to white dwarf (WD) binaries. We argue that the observed correlation is a natural consequence of the Keplerian disk flow adjustment to the innermost sub-Keplerian boundary conditions near the central object. In the framework of the transition layer model the high frequency is related to the Keplerian frequency at the outer (adjustment) radius and the low frequency is related to the magnetoacoustic oscillation (MA) frequency. Using a relation between the MA frequency the magnetic and gas pressure and the density and the hydrostatic equilibrium condition in the disk we infer a linear correlation the Keplerian frequency and the MA frequency. We estimate the magnetic field strength near the TL outer radius for BHs NSs and WDs. The fact that the observed high-low frequency correlation over five orders of magnitude is valid for BHs, NSs, and down to WDs strongly rules out relativistic models for QPO phenomena. We come to the conclusion that the QPOs observations indicate the adjustment of the geometrically thin disk to sub-Keplerian motion near the central object. This effect is a common feature for a wide class of systems, starting from white dwarf binaries up to black hole binaries.Comment: 8 pages, 1 figure, accepted for publication in the ApJ. Letters 2002 August

    Chandra Observation of the Dipping Source XB 1254-690

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    We present the results of a 53 ks long Chandra observation of the dipping source XB 1254--690. During the observation neither bursts or dips were observed. From the zero-order image we estimated the precise X-ray coordinates of the source with a 90% uncertainty of 0.6\arcsec. Since the lightcurve did not show any significant variability, we extracted the spectrum corresponding to the whole observation. We confirmed the presence of the \ion{Fe}{xxvi} Kα_\alpha absorption lines with a larger accuracy with respect to the previous XMM EPIC pn observation. Assuming that the line width were due to a bulk motion or a turbulence associated to the coronal activity, we estimate that the lines were produced in a photoionized absorber between the coronal radius and the outer edge of the accretion disk.Comment: 8 pages, 10 figs, accepted by A&A on 6 December 200

    An XMM-Newton view of the dipping low-mass X-ray binary XTE J1710-281

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    (abridged) We analyzed the archived XMM-Newton observation of the poorly studied low-mass X-ray binary XTE J1710-281 performed in 2004 that covered one orbital period of the system (3.8 hr). The source shows dips as well as eclipses, hence it is viewed close to edge-on. We modeled the spectral changes between persistent and dips in the framework of the partial covering model and the ionized absorber approach. The persistent spectrum can be fit by a power law with a photon index of 1.94(+-0.02) affected by absorption from cool material with a hydrogen column density of 0.401(+-0.007)*10^22 cm^-2. The spectral changes from persistent to deep-dipping intervals are consistent with the partial covering of the power-law emission, with the covering fraction increasing from 26% during shallow dipping to 78% during deep dipping. We do not detect any absorption lines from highly ionized species such as FeXXV. The upper-limits we derive on their equivalent width (EW) are not constraining. Despite not detecting any signatures of a warm absorber, we show that the spectral changes are consistent with an increase in column density (4.3(-0.5;+0.4)*10^22 cm^-2 during shallow dipping to 11.6(-0.6;+0.4)*10^22 cm^-2 during deep dipping) and a decrease in ionization state of a highly-ionized absorber (10^2.52 during shallow dipping to 10^2.29 erg.s^-1.cm during deep dipping), associated with a slight increase in the column density of a neutral absorber. The parameters of the ionized absorber are not constrained during persistent emission. The warm absorber model better accounts for the ~1 keV depression visible in the pn dipping spectra, and naturally explains it as a blend of lines and edges unresolved by pn. A deeper observation of XTE J1710-281 would enable this interpretation to be confirmed.Comment: 9 pages, 6 figures, accepted for publication in Astronomy and Astrophysic

    Spectral changes during dipping in low-mass X-ray binaries due to highly-ionized absorbers

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    X-ray observations have revealed that many microquasars and low-mass X-ray binaries (LMXBs) exhibit narrow absorption features identified with resonant absorption from Fe XXV and 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 both the 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 4U 1323-62. 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.Comment: 19 pages, 11 figures, accepted for publication by Astronomy and Astrophysic

    Discovery of X-ray absorption features from the dipping low-mass X-ray binary XB 1916-053 with XMM-Newton

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    We report the discovery of narrow Fe XXV and Fe XXVI K alpha X-ray absorption lines at 6.65 and 6.95 keV in the persistent emission of the dipping low-mass X-ray binary (LMXB) XB 1916-053 during an XMM-Newton observation performed in September 2002. In addition, there is marginal evidence for absorption features at 1.48 keV, 2.67 kev, 7.82 keV and 8.29 keV consistent with Mg XII, S XVI, Ni XXVII K alpha and Fe XXVI K beta transitions, respectively. Such absorption lines from highly ionized ions are now observed in a number of high inclination (ie. close to edge-on) LMXBs, such as XB 1916-053, where the inclination is estimated to be between 60-80 degrees. This, together with the lack of any orbital phase dependence of the features (except during dips), suggests that the highly ionized plasma responsible for the absorption lines is located in a cylindrical geometry around the compact object. Using the ratio of Fe XXV and Fe XXVI column densities, we estimate the photo-ionization parameter of the absorbing material to be 10^{3.92} erg cm s^{-1}. Only the Fe XXV line is observed during dipping intervals and the upper-limits to the Fe XXVI column density are consistent with a decrease in the amount of ionization during dipping intervals. This implies the presence of cooler material in the line of sight during dipping. We also report the discovery of a 0.98 keV absorption edge in the persistent emission spectrum. The edge energy decreases to 0.87 keV during deep dipping intervals. The detected feature may result from edges of moderately ionized Ne and/or Fe with the average ionization level decreasing from persistent emission to deep dipping. This is again consistent with the presence of cooler material in the line of sight during dipping.Comment: 13 pages, accepted for publication in Astronomy and Astrophysic
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