ON THE SIZE AND LOCATION OF THE X-RAY EMITTING CORONAE AROUND BLACK HOLES

Abstract

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