Rapidly Variable Fe Kα Line in NGC 4051

We present a detailed analysis on the variability of the Fe K emission line in NGC 4051 using ASCA data. Through simple Gaussian line fits, we find not only obvious Fe K line variability with no significant difference in the X-ray continuum flux between two ASCA observations that were separated by ~ 440 days, but also rapid variability of the Fe K line on timescales ~104 s within the second observation. During the second observation, the line is strong (EW=733+206?219 eV) and broad (?=0.96+0.49?0.35 keV) when the source is brightest and becomes weaker (EW=165+87?86 eV) and narrower (?<0.09 keV) while the source is weakest. The equivalent width of the Fe K line correlates positively with the continuum flux, which shows an opposite trend with another Seyfert type 1 galaxy, MCG -6-30-15.