Leaving the ISCO: the inner edge of a black-hole accretion disk at various luminosities

Understand

The "radiation inner edge" of an accretion disk is defined as the inner boundary of the region from which most of the luminosity emerges.

• Similarly, the "reflection edge" is the smallest radius capable of producing a significant X-ray reflection of the fluorescent iron line.
• For black hole accretion disks with very sub-Eddington luminosities these and all other "inner edges" locate at ISCO.
• Thus, in this case, one may rightly consider ISCO as the unique inner edge of the black hole accretion disk.