Joint consideration of X-ray timing data in conjunction with time resolved spectroscopy allows us to detect and interpret lags within the X-ray band and thus tackle several key questions in AGN research, i.e.
- what is the origin of the time lags between different X-ray bands
- what are the distance, global covering, physical state, velocity and mass of the X-ray reprocessing gas
AND
- what constraints can be obtain on the X-ray reprocessor from observations in other wavebands.
I consider results from existing X-ray data, and pose the question as to what new observations would be most valuable for forward progress, using existing available satellites.