What happens to gravity after matter-antimatter collision that result in all photon and not other particles?

Before the collision, both particle warp space-time. Since photon does not warp space-time, what happened to the warping? Does it disappear and "spring" back to flat? Is there any "ringing" or damped response ociated with this springiness or is it instantaneous? If it's instantaneous, does it release graviton as a result? If it's finite, is there a wave of space-time disturbance for every matter->photon decay?