Reconnection in Marginally Collisionless Accretion Disk Coronae

We point out that a conventional construction placed on observations of accreting black holes, in which their nonthermal X-ray spectra are produced by inverse Comptonization in a coronal plasma, suggests that the plasma is marginally collisionless. Recent developments in plasma physics indicate that fast reconnection takes place only in collisionless plasmas. As has recently been suggested for the Sun's corona, such marginal states may result from a combination of energy balance and the requirements of fast magnetic reconnection.