Powerful flares from recoiling black holes in quasars

Mergers of spinning black holes can give recoil velocities from gravitational radiation up to several thousand km s(-1). A recoiling supermassive black hole in an AGN retains the inner part of its accretion disk. Marginally bound material rejoining the disk around the moving black hole releases a large amount of energy in shocks in a short time, leading to a flare in thermal soft X-rays with a luminosity approaching the Eddington limit. Reprocessing of the X-rays by the infalling material gives strong optical and ultraviolet emission lines with a distinctive spectrum. Despite the short lifetime of the flare (similar to 10(4) yr), as many as 10(2) flares may be in play at the present time in QSOs at redshifts similar to 1-3. These flares provide a means to identify high-velocity recoils.