  We report time and angle resolved spectroscopic measurements in optimally
doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. The spectral function is monitored as
a function of temperature, photoexcitation density and delay time from the pump
pulse. According to our data, the superconducting gap becomes slightly stiffer
when moving off the nodal direction. The nodal quasiparticles develop a faster
dynamics when pumping the superconductor with a fluence that is large enough to
induce the total collapse of the gap. We discuss the observed relaxation in
terms of a dynamical reformation of Cooper pairs.
