Narrow Moving Fe K-alpha lines from magnetic flares in AGN

Abstract

We point out that luminous magnetic flares, thought to occur in standard AGN accretion disks, cannot be located much higher than few pressure scale heights above the disk. Using this fact, we estimate the fraction of the disk surface illuminated by a typical flare. This fraction turns out to be very small for geometrically thin disks, which implies that the instantaneous Fe K-alpha emission line from a specific magnetic flare is narrow. The line is red- or blue-shifted depending on the position of the observer relative to the flare and sweeps across the line band with time. We present several examples of theoretical time-resolved line profiles from such flares for a non-rotating black hole. The observations of such moving features with future X-ray telescopes will present a powerful test of the accretion disk geometry and may also test General Relativity in the strong field limit.