  Here we report our recent study on the spectral energy distribution (SED) of
the high frequency BL Lac object Mrk 421 in different luminosity states. We
used a full-fledged chi2-minimization procedure instead of more commonly used
"eyeball" fit to model the observed flux of the source (from optical to very
high energy), with a Synchrotron-Self-Compton (SSC) emission mechanism. Our
study shows that the synchrotron power and peak frequency remain constant with
varying source activity, and the magnetic field decreases with the source
activity while the break energy of electron spectrum and the Doppler factor
increase. Since a lower magnetic field and higher density of electrons result
in increased electron-photon scattering efficiency, the Compton power
increases, so does the total emission.
