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 which were separated by \sim 440 days , but also rapid variability of Fe K line on time scales \sim 10 ^ { 4 } s within the second observation .
During the second observation , the line is strong ( EW = 733 ^ { +206 } _ { -219 } eV ) and broad ( \sigma = 0.96 ^ { +0.49 } _ { -0.35 } keV ) when the source is brightest , and become weaker ( EW = 165 ^ { +87 } _ { -86 } eV ) and narrower ( \sigma < 0.09 keV ) whilst the source is weakest .
The equivalent width of Fe K line correlates positively with the continuum flux , which shows an opposite trend with another Seyfert 1 galaxy MCG –6-30-15 .