Variability of the iron K-emission line in the Seyfert 1 galaxy NGC 3516
  We present strong evidence for variability of the flux of the iron K$\alpha$ emission line in the Seyfert 1 galaxy, NGC 3516. Two ASCA observations, separated by $\sim 1$~yr, showed a marked decrease in continuum flux by $\sim 60$~per cent. The flux in the broad, iron K$\alpha$ line decreased by the same factor in this time period, with no evidence for changes in the line profile. The line variability is significant at $>99$~per cent confidence and rules out models in which the line is produced in a molecular torus located at $>1$~pc from the nucleus. An accretion disk is considerably more likely. 
K. Nandra, R.F. Mushotzky, T. Yaqoob, I.M. George, T.J. Turner (LHEA,   NASA/GSFC)