The author analyses two particularly significant cosmic gamma-ray bursts recorded by the French-Soviet experiment APEX on board the space mission PHOBOS. The October 24th 1988 event, lasting more than 16 seconds, is among the strongest events observed up to now. The very high temporal resolution available for its light curve allows to study the power spectrum density up to a frequency range more extended than in the past. The August 10th 1988 event, lasting about 1 second, recorded with a temporal resolution higher than in the precedent one, permits to reach still higher frequencies. The authors discuss the results of their analysis, comparing them with the results obtained for other events recorded by precedent space missions, and giving interpretative suggestions.