Iron line reverberation mapping with Constellation-X

The broad X-ray iron line seen in the spectra of many active galactic nucle i (AGNs) is thought to originate from the inner regions of the putative bla ck hole accretion disk and hence provides a rare probe of that central regi on. In principle, future high-throughput X-ray spectrometers should be able to examine the temporal response of this fluorescent line to flares in the X-ray continuum source (which energizes this emission line)-i.e., iron lin e reverberation mapping will be possible. It has been previously found that there are robust reverberation signatures of the black hole spin, mass, an d the X-ray flare location above the accretion disk. Here, we simulate obse rvations of a bright Seyfert nucleus with the proposed NASA mission Constel lation-X and demonstrate the feasibility of detecting these reverberation s ignatures with this mission. Hence, starting with XMM in 1999 and maturing with Constellation-X in ca. 2010, iron line reverberation will open a new w indow on the innermost regions of AGNs.