The Effects of Relativistic Bulk Motion of X‐Ray Flares in the Corona on the Iron Kα Line in Seyfert 1 Galaxies

We study the effects of the bulk motion of X-ray flares on the shape andequivalent width of the iron Kalpha line from an untruncated cold disk around aKerr black hole using fully relativistic calculations. The flares are locatedabove a cold accretion disk -- either on or off the rotation axis. For on- oroff-axis flares, the upward/outward bulk motion causes a reduction of the ironKalpha line width. To a distant observer with a low inclination angle (\theta_o\simlt 30deg.), larger upward/outward bulk velocities decrease the extension ofthe red wing, with little change in the location of the blue `edge'. Incontrast, an observer at a large inclination angle (e.g. \theta_o=60deg.) seesboth the red wing and the blue `edge' change with the bulk velocity. Theequivalent width of the iron Kalpha line decreases rapidly with increasing bulkvelocity of flares. However, the `narrower' line profiles observed in someobjects (e.g. IC4329A and NGC4593) are difficult to produce using theout-flowing magnetic flare model with an appropriate equivalent width unlessthe X-ray emission is concentrated in an outer region with a radius of severaltens of r_g=GM/c^2 or more. An important result is that the iron Kalpha lineintensity is found to be constant even though the continuum flux variessignificantly, which is true for out-flowing magnetic flares with differentbulk velocities but similar intrinsic luminosities when located close to thecentral black hole. We find that fluctuations in the bulk velocities ofout-flowing low-height flares located at the inner region (r\simlt 15r_g) canaccount for a constant iron Kalpha line and significant continuum variation asobservered in MCG-6-30-15 and NGC5548. (Abridged)Comment: 30 pages (including 8 figures); minor changes, to appear in ApJ, Nov. 10, 200