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A gamma ray burst produces somewhere around 1044 J of energy, according to Wikipedia. Only a small portion of that energy will be absorbed by other objects.
The rest of that energy will go on to travel the universe indefinitely I presume?
How do we know how much of the universes total mass-energy is in "in transit" in the form of gamma rays and other forms of radiation?
The energy density of the universe is quite well known. Most seems in the form of what is called "dark energy", which accelerates cosmic expansion. Next comes dark matter, accounting for some 20%, then baryonic matter, about 4%. Electromagnetic radiation (photons) contributes so little that I forgot how much. Most of the energy density in photons is in the cosmic background (CMB), the remnant of an ealier epoch when electromagnetic radiation dominated the energy budget of the universe.
The cosmic expansion makes the energy density of photons decay faster than that of matter, because (in addition to the decrease in spatial density $\propto(1+z)^{-3}$) photons also get red-shifted, adding another factor $(1+z)^{-1}$.
No energy is in transit as GRBs, just like Gamma rays that started in a GRB.
If you remember that all that energy is in the form of radiation, it obeys the same laws as ordinary light: the farther, the dimmer (inverse of square of the distance law).
So if you see stars dimmer as they are farther from you, same happens to the RGBs. Radiation from the stars expands infinitely (becoming dimmer and dimmer) until absorbed by clouds or just becoming dimmer than the background.
Same happens to gamma rays from GRBs. It is just that since rays are more energetic, they are less easily absorbed, and since GRBs themselves are more energetic, the becoming dimmer than background distance is bigger.
