Comparison of spectral models for disc truncation in the hard state of GX 339–4

Abstract

We probe models of disc truncation in the hard spectral state of an outburst of the well-known X-ray transient GX 339-4. We test a large number of different models of disc reflection and its relativistic broadening, using two independent sets of codes, and apply it to a Rossi X-ray Timing Explorer spectrum in the rising part of the hard state of the 2010/11 outburst. We find our results to be significantly model-dependent. While all of the models tested show best-fits consistent with truncation, some models allow the disc to extend close to the innermost stable circular orbit (ISCO) and some require substantial disc truncation. The different models yield a wide range in best-fit values for the disc inclination. Our statistically best model has a physical thermal Comptonization primary continuum, requires the disc to be truncated at a radius larger than or equal to about two ISCO radii for the maximum dimensionless spin of 0.998, and predicts a disc inclination in agreement with that of the binary. Our preferred models have moderate Fe abundance, 2 times solar. We have also tested the effect of increasing the density of the reflecting medium. We find it leads to an increase in the truncation radius, but also to an increase in the Fe abundance, opposite to a previous finding.

Towards Precision Measurements of Accreting Black Holes Using X-Ray Reflection Spectroscopy

“…Significant truncation in BH binaries is also implied by considering the re-emission of the X-rays absorbed by the disk (Zdziarski & De Marco 2020), in agreement with the disk truncation found by reflection spectroscopy in some studies (e.g., Plant et al 2015, Basak & Zdziarski 2016, Dzie lak et al 2019. For a truncated disk, the relativistic distortion of reflection from the surrounding cold disk is weak and applications of reflection models allow to estimate geometrical parameters of the disk, like the truncation radius or the inclination angle, but not the BH spin.…”

Spectral and temporal properties of Compton scattering by mildly relativistic thermal electrons

“…On the other hand, X-ray sources in most of accreting black-hole binaries and AGNs appear to have sizes of ∼ 10 1 -10 3 R g (e.g., Done et al 2007;De Marco et al 2013, 2015Chartas et al 2016;Bernardini et al 2016;Dziełak et al 2019;Mahmoud, Done, & De Marco 2019). This rules out the observed long hard X-ray lags (e.g., in Cyg X-1, Miyamoto & Kitamoto 1989;Kotov, Churazov, & Gilfanov 2001) to be due to time lag between subsequent scatterings in a hot plasma.…”

Disk, Corona, Jet Connection in the Intermediate State of MAXI J1820+070 Revealed by NICER Spectral-timing Analysis

“…Despite the ubiquity of the non-thermal X-ray emission, the fundamental properties of the corona are not well understood (Done et al 2007). The difficulty lies in the fact that the innermost region of BHBs are too compact to be resolved via imaging, and it is challenging for X-ray spectroscopy alone to distinguish the underlying continuum models (e.g., single or double Comptonization regions; Dziełak et al 2019) from which the geometry and formation of the corona could then be inferred. There are three different types of coronal models: radiatively inefficient accretion flow (RIAF) within the truncated accretion disk (advection-dominated accretion flow or other types of coronal flow; Ferreira et al 2006;Narayan & McClintock 2008), static corona with different configurations (e.g., slab; Haardt et al 1994), and the corona being the base of a jet (Markoff et al 2001(Markoff et al , 2005.…”