On the size and location of the X-ray emitting coronae around black holes

TL;DR

This paper uses advanced imaging and timing data to show that X-ray emitting coronae around black holes are highly compact, located within about 20 gravitational radii of the accretion disk, especially in luminous black holes.

Contribution

It provides strong observational evidence that black hole coronae are very compact and close to the black hole, supporting models involving magnetic reconnection and jet bases.

Findings

Coronal regions are within ~20 gravitational radii of the black hole.

Results are consistent across various systematic uncertainties.

Supports models of magnetic reconnection and jet base origins for X-ray emission.

Abstract

The observation of energetic X-ray emission from black holes, inconsistent with thermal emission from an accretion disk, has long indicated the presence of a "corona" around these objects. However, our knowledge of the geometry, composition, and processes within black hole coronae is severely lacking. Basic questions regarding their size and location are still a topic of debate. In this letter, we show that for black holes with luminosities $L\gtrsim10^{-2}L_{Edd}$ -- characteristic of many Seyferts, quasars, and stellar-mass black holes (in their brighter states) -- advanced imaging and timing data strongly favor X-ray emitting regions that are highly compact, and only a few Gravitational radii above the accretion disk. The inclusion of a large number of possible systematics uncertainties does not significantly change this conclusion with our results still suggesting emission from within $\sim20$\rg\ in all cases. This result favors coronal models wherein most of the hard X-ray emission derives from magnetic reconnection in the innermost disk and/or from processes in the compact base of a central, relativistic jet.