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Register a new userEcho Tomography of Sco X-1 using Bowen Fluorescence Lines
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J. Casares
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We present preliminary results of a simultaneous X-ray/optical campaign of the prototypical LMXB Sco X-1 at 1-10 Hz time resolution. Lightcurves of the high excitation Bowen/HeII emission lines were obtained through narrow interference filters with ULTRACAM, and these were cross-correlated with X-ray lightcurves. We find evidence for correlated variability, in particular when Sco X-1 enters the Flaring Branch. The Bowen/HeII lightcurves lag the X-ray lightcurves with a light travel time which is consistent with reprocessing in the companion star.
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We present simultaneous high time resolution (1-10 Hz) X-ray and optical observations of the persistent LMXBs Sco X-1 and V801 Ara(=4U 1636-536). In the case of Sco X-1 we find that the Bowen/HeII emission lags the X-ray light-curves with a light travel time of ~11-16s which is consistent with reprocessing in the donor star. We also present the detection of three correlated X-ray/optical bursts in V801 ara. Although this latter project is still in progress our preliminary results obtained by subtracting the Continuum light-curve from the Bowen/HeII data provide evidence of orbital phase dependent echoes from the companion star.
This paper will review a new technique of detecting companion stars in LMXBs and X-ray transients in outburst using the Bowen fluorescence lines at 4634-4640 Angs. These lines are very efficiently reprocessed in the atmospheres of the companion stars, and thereby provide estimates of the K2 velocities and mass functions. The method has been applied to Sco X-1, X1822-371 and GX339-4 which, in the latter case, provides the first dynamical evidence for the presence of an accreting black hole. Preliminary results from a VLT campaign on V801 Ara, V926 Sco and XTE J1814-338 are also presented.
We study hard X-ray emission of the brightest accreting neutron star Sco X-1 with INTEGRAL observatory. Up to now INTEGRAL have collected ~4 Msec of deadtime corrected exposure on this source. We show that hard X-ray tail in time average spectrum of Sco X-1 has a power law shape without cutoff up to energies ~200-300 keV. An absence of the high energy cutoff does not agree with the predictions of a model, in which the tail is formed as a result of Comptonization of soft seed photons on bulk motion of matter near the compact object. The amplitude of the tail varies with time with factor more than ten with the faintest tail at the top of the so-called flaring branch of its color-color diagram. We show that the minimal amplitude of the power law tail is recorded when the component, corresponding to the innermost part of optically thick accretion disk, disappears from the emission spectrum. Therefore we show that the presence of the hard X-ray tail may be related with the existence of the inner part of the optically thick disk. We estimate cooling time for these energetic electrons and show that they can not be thermal. We propose that the hard X-ray tail emission originates as a Compton upscattering of soft seed photons on electrons, which might have initial non-thermal distribution.
Sco X-1, the brightest low mass X-ray binary, is likely to be a source for gravitational wave emission. In one mechanism, emission of a gravitational wave arrests the increase in spin frequency due to the accretion torque in a low mass X-ray binary. Since the gravitational waveform is unknown, a detection method assuming no apriori knowledge of the signal is preferable. In this paper, we propose to search for a gravitational wave from Sco X-1 using a {{it source tracking}} method based on a coherent network analysis. In the method, we combine data from several interferometric gravitational wave detectors taking into account of the direction to Sco X-1, and reconstruct two polarization waveforms at the location of Sco X-1 in the sky as Sco X-1 is moving. The source tracking method opens up the possibility of searching for a wide variety of signals. We perform Monte Carlo simulations and show results for bursts, modeled, short duration periodic sources using a simple excess power and a matched filter method on the reconstructed signals.
A new measure of reddening (E$_{(B-V)}$$sim$0.00) has been obtained from the comparison between the observed and the theoretical intensity decrement for 20 emission lines of the $ion{He}{ii}$ Fowler (n$to$3) series. This value has been confirmed by the STIS and IUE continuum distribution, and by the value of n$_H$ from the damped profile of the IS H Ly-$alpha$ line. We have obtained very accurate measurements for about thirty Bowen lines of $ion{O}{iii}$ and a precise determination of the efficiency in the O1 and O3 excitation channels (18 % and 0.7 %, respectively). The relative $ion{O}{iii}$ intensities are in good agreement with the predictions by Froese Fischer (1994). A detailed study of the decays from all levels involved in the Bowen mechanism has lead to the detection of two new $ion{O}{iii}$ Bowen lines near $lambda$ 2190. High resolution IUE data have shown a nearly linear decline with time, from 1978 to 1995, in the efficiency of the O1 and O3 processes, with a steeper slope for the O3 channel. A detailed study of the $ion{N}{iii}$ $lambda$ 4640 lines and of their excitation mechanism has shown that, recombination and continuum fluorescence being ruled out, line fluorescence remains the only viable mechanism to pump the 3d $^2D_{5/2}$ and 3d $^2D_{3/2}$ levels of $ion{N}{iii}$. We point out the important role of multiple scattering in the resonance lines of $ion{O}{iii}$ and $ion{N}{iii}$ near $lambda$ 374 and show that the observed $ion{N}{iii}$ line ratios and intensities can be explained in terms of line fluorescence by the three resonance lines of $ion{O}{iii}$ at $lambda$$lambda$ 374.432, 374.162 and 374.073 under optically thick conditions.
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