  We present the results of 3-dimensional kinetic simulations and theoretical
studies on the formation and evolution of the current sheet in a collisionless
plasma during magnetic field annihilation in the ultra-relativistic limit.
Annihilation of oppositively directed magnetic fields driven by two laser
pulses interacting with underdense plasma target is accompanied by an
electromagnetic burst generation. The induced strong non-stationary
longitudinal electric field accelerates charged particles within the current
sheet. Properties of the laser-plasma target configuration are discussed in the
context of the laboratory modeling for charged particle acceleration and gamma
flash generation in astrophysics.
