Measuring the relativistic transfer function in NGC 4151

XMM has been at the forefront of the recent discovery Xray relativisticreverberation. Short Fe K delays have been observed in seven objects. To advancebeyond mere detections, we propose to observe the bright AGN NGC 4151 for 350 ksto directly measure the relativistic transfer function, which encodes thegeometry, dynamics and the way spacetime alters the path of light through thepotential of the black hole. NGC 4151 is the ideal laboratory for such anexperiment because of its brightness, variability and the existing reverberationlags. Combing the new and archival data will allow us to measure the Fe Kresponse at many timescales providing a first direct measurement of thetransfer function. XMM is currently the only telescope capable of achieving such a legacy goal prior to Athena. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]