Pulse emission from relativistic collapsing objects

We discuss observable form of the radiation emitted from a surface of a collapsing object using a simplified model in which a radiation of massless particles has a sharp in time profile and it happens at the surface at the same moment of comoving time. Its redshift and bending angle are affected by the strong gravitational field. We obtain a simple expression for the observed flux of the radiation as a function of time. To find an explicit expression for the flux we develop an analytical approximation for the bending angle and time delay for null rays emitted by a collapsing surface at R > 2Rg . We obtain an approximate analytical expression for the observed flux and study its properties.