  The existence of strong correlation between the peak luminosity (and/or
bolometric energetics) of Gamma Ray Bursts (GRB) is one of the most intrigue
problem of GRB physics. This correlation is not yet understood. Here we
demonstrate that this correlation can be explained in framework of synchrotron
self-absorption (SSA) mechanism of GRB prompt emission. We estimate the
magnetic field strength of the central engine at the level $B\sim 10^{14}
(10^3/\Gamma)^3 (1+z)^2$, where $\Gamma$ is the Lorentz factor of fireball.
