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Register a new userSpectral analysis of the XMM-Newton data of GX 339-4 in the low/hard state: disc truncation and reflection
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Added by
Andrzej A. Zdziarski
Publication date
2015
fields
Physics
and research's language is
English
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We analyse all available observations of GX 339--4 by XMM-Newton in the hard spectral state. We jointly fit the spectral data by Comptonization and the currently best reflection code, relxill. We consider in detail a contribution from a standard blackbody accretion disc, testing whether its inner radius can be set equal to that of the reflector. However, this leads to an unphysical behaviour of the disc truncation radius, implying the soft X-ray component is not a standard blackbody disc. This appears to be due to irradiation by the hard X-rays, which strongly dominate the total emission. We consider a large array of models, testing, e.g., the effects of the chosen energy range, of adding unblurred reflection, and assuming a lamppost geometry. We find the effects of relativistic broadening to be relatively weak in all cases. In the coronal models, we find the inner radius to be large. In the lamppost model, the inner radius is unconstrained, but when fixed to the innermost stable orbit, the height of the source is large, which also implies a weak relativistic broadening. In the former models, the inner radius correlates with the X-ray hardness ratio, which is consistent with the presence of a truncated disc turning into a complete disc in the soft state. We also find the degree of the disc ionization to anti-correlate with the hardness, leading to strong spectral broadening due to scattering of reflected photons in the reflector in the softest studied states.
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Black hole X-ray binaries display large outbursts, during which their properties are strongly variable. We develop a systematic spectral analysis of the 3-40 keV RXTE/PCA data in order to study the evolution of these systems and apply it to GX 339-4. Using the low count rate observations, we provide a precise model of the Galactic background at GX 339-4s location and discuss its possible impact on the source spectral parameters. At higher fluxes, the use of a Gaussian line to model the reflection component can lead to the detection of a high-temperature disk, in particular in the high-hard state. We demonstrate that this component is an artifact arising from an incomplete modeling of the reflection spectrum.
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