The Effect of Returning Radiation on Relativistic Reflection

Understand

We study the effect of returning radiation on the shape of the X-ray reflection spectrum in the case of thin accretion disks.

• We show that the returning radiation mainly influences the observed reflection spectrum for a large black hole spin (a > 0.9) and a compact primary source of radiation close to the black hole at height h < 5 $r_\mathrm{g}$, and that it dominates the reflected flux for extreme values of spin and compactness.
• The main effect of the returning radiation is to increase the irradiating flux on to the outer parts of the accretion disk, leading to stronger reflection and a flatter overall emissivity profile.
• By analyzing simulated observations we show that neglecting returning radiation in existing studies of reflection dominated sources has likely resulted in overestimating the height of the corona above the black hole.