Exploring the radial disc ionization profile of the black hole X-ray binary GRS 1915+105

Understand

Accreting black holes show characteristic 'reflection' features in their X-ray spectra, including the iron K$\alpha$ fluorescence line, which result from X-rays radiated by a compact central corona being reprocessed in the accretion disc atmosphere.

• The observed line profile is distorted by relativistic effects, providing a diagnostic for disc geometry.
• Nearly all previous X-ray reflection spectroscopy studies have made the simplifying assumption that the disc ionization state is independent of radius in order to calculate the restframe reflection spectrum.
• However, this is unlikely to be the case in reality, since the irradiating flux should drop off steeply with radius.