Pair plasma dominance in the 3C 279 jet on parsec scales

We have investigated whether a pc-scale jet of 3C 279 is dominated by a nor mal plasma or an electron-positron plasma. By analyzing Very Long Baseline Interferometry data between 1983 and 1990, and utilizing the theory of sync hrotron self-absorption, we have derived the lower limits for the proper el ectron number density. Comparing the lower limit with another independent c onstraint for the electron density that is deduced from the kinetic luminos ity, we find that the core and components C3 and C4 are likely dominated by an electron-positron plasma.