Coronal geometry at low mass-accretion rates from XMM and NuSTAR spectra
Abstract
At very low Eddington luminosities the structure and physics of the accretion flow around a black hole are still debated, in particular in the inner most regions. By making sensitive measurements of the relativistic blurring of the X-ray reflection spectrum we investigate these physics, a task for which XMM-Newton, in combination with hard X-ray coverage provided by NuSTAR or Hitomi, is ideally suited and will continue to be unique for years to come. I will present results from XMM and NuSTAR observations of the radio-galaxy Cen A and of the X-ray binary GRS 1739-278 during the decline of its outburst. While Cen A shows a prominent iron line, the broad-band spectrum shows no evidence of reflection. This lack of reflection can best be explained by a jet origin of the hard X-rays or a significantly truncated accretion disk. The iron line can be self-consistently explained when assuming an optically thick torus surrounding the super-massive black-hole. The broad-band X-ray spectrum of GRS 1739-278 can be well described by a simple power-law or Comptonization continuum. A weak relativistic reflection model results in a small but significant improvement of the statistical quality of the fit. This relativistic model indicates a strongly truncated disk.
- Publication:
-
XMM-Newton: The Next Decade
- Pub Date:
- June 2016
- Bibcode:
- 2016xnnd.confE..45F