Special relativistic effects on the strength of the fluorescent K iron line from black hole accretion discs

The broad iron K$\alpha$ emission line, commonly seen in the X-ray spectrumof Seyfert nuclei, is thought to originate when the inner accretion disk isilluminated by an active disk-corona. We show that relative motion between thedisk and the X-ray emitting material can have an important influence on theobserved equivalent width (EW) of this line via special relativistic aberrationand Doppler effects. We suggest this may be relevant to understanding why theobserved EW often exceeds the prediction of the standard X-ray reflectionmodel. Several observational tests are suggested that could disentangle thesespecial relativistic effects from iron abundance effects.