X-ray Reflection from the Plunging Region of Black Hole Accretion Disks

Understand

Accretion around black holes is very often characterized by distinctive X-ray reflection features (mostly, iron inner-shell transitions), which arise due to the primary radiation being reprocessed by a dense and relatively colder medium, such as an accretion disk.

• Most reflection modeling assume that emission stops at the inner-most stable circular orbit (ISCO), and that for smaller radii - in the plunging region - the density drops and the accretion flow is far too ionized for efficient line production.
• We investigate the spectral features of the reflection in the plunging regions of optically-thick and geometrically-thin accretion disks around black holes.
• We show that for cases in which the density profile is considered constant (as expected in highly magnetized flows), or in cases in which the disk density is high enough such that the ionization still allows line formation within the ISCO, there is a significant modification of the observed reflected spectrum.