Iron Line Reverberation Mapping with Constellation-X

The broad X-ray iron line seen in the spectra of many active galactic nuclei (AGNs) is thought to originate from the inner regions of the putative black hole accretion disk and hence provides a rare probe of that central region. 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 line reverberation mapping will be possible. It has been previously found that there are robust reverberation signatures of the black hole spin, mass, and the X-ray flare location above the accretion disk. Here, we simulate observations of a bright Seyfert nucleus with the proposed NASA mission Constellation-X and demonstrate the feasibility of detecting these reverberation signatures with this mission. Hence, starting with XMM in 1999 and maturing with Constellation-X in ca. 2010, iron line reverberation will open a new window on the innermost regions of AGNs.