Spectral analysis of theXMM–Newtondata of GX 339–4 in the low/hard state: disc truncation and reflection

Abstract

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.

On the Lamppost Model of Accreting Black Holes

“…On the other hand, we find no pairs in the X-ray source in the hard state of GX 339-4 when we use the sizes estimated from fitting X-ray spectra by Basak & Zdziarski (2016) and from reverberation by De Marco et al (2015). They both found r in ∼d  30 at the highest observed L/L Edd ; 0.15, implying ℓ  10 2 .…”

“…This is illustrated in Figure 1 (see also Basak & Zdziarski 2016). For E c = 150 keV, the spectrum of xillver becomes incorrect at E  150 keV.…”

Accretion Disks and Coronae in the X-Ray Flashlight

“…These results have been debated in several other works (e.g. Done and Diaz Trigo 2010;Kolehmainen et al 2014;Plant et al 2015;Basak and Zdziarski 2016;Basak et al 2017), but some of this criticism has been rebutted (e.g. Cackett and Miller 2013;Chiang et al 2016).…”

The Mass Function of GX 339–4 from Spectroscopic Observations of Its Donor Star*

“…Modeling of the reflection component of the X-ray spectra of GX 339−4 has yielded inclinations ranging from 30°to 60°( e.g., Fürst et al 2015;García et al 2015;Basak & Zdziarski 2016;Parker et al 2016). An inclination in this range would lead to a BH mass between~-4 20 M e (see Figure 7).…”