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

Abstract

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. Here we analyse a Nuclear Spectroscopic Telescope ARray observation of GRS 1915+105 that exhibits strong reflection features. We find that using a self-consistently calculated radial ionization profile returns a better fit than assuming constant ionization. Our results are consistent with the inner disc being radiation pressure dominated, as is expected from the high inferred accretion rate for this observation. We also find that the assumed ionization profile impacts on the best fitting disc inner radius. This implies that the black hole spin values previously inferred for active galactic nuclei and X-ray binaries by equating the disc inner radius with the innermost stable circular orbit may be changed significantly by the inclusion of a self-consistent ionization profile.

Accepted for publication in MNRAS

References in corpus (10)

• Modelling the behaviour of accretion flows in X-ray binaries
• A Parallax Distance to the Microquasar GRS 1915+105 and a Revised Estimate of its Black Hole Mass
• A quasi-periodic modulation of the iron line centroid energy in the black hole binary H 1743-322
• No Time for Dead Time: Timing analysis of bright black hole binaries with NuSTAR
• A public relativistic transfer function model for X-ray reverberation mapping of accreting black holes
• High Density Reflection Spectroscopy I. A case study of GX~339-4
• Tomographic reflection modelling of quasi-periodic oscillations in the black hole binary H 1743-322
• An X-ray reverberation mass measurement of Cygnus X-1
• Steep X-ray reflection emissivity profiles in AGN as the result of radially-structured disc ionisation
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Cited by in corpus (5)

• Phase-resolved spectroscopy of a quasi-periodic oscillation in the black hole X-ray binary GRS 1915+105 with NICER and NuSTAR
• Multi-timescale reverberation mapping of Mrk 335
• Testing evolution of LFQPOs with mass accretion rate in GRS 1915+105 with Insight-HXMT
• Impact of the reflection model on the estimate of the properties of accreting black holes
• X-ray spectral correlations in a sample of Low-mass black hole X-ray binaries in the hard state