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Description
Gamma-ray bursts (GRBs) are the most powerful transient explosions in the Universe and emit a vast amount of their energy in the form of gamma-rays. Although they last extremely short on cosmic time scales, their gamma-ray emission shows a wealth of temporal variability. Properties of this variability may carry information about the processes the gamma-rays emerge from, which remain poorly understood. This research investigates the redshift-corrected gamma-ray light curves of GRBs with known redshift, and the observer-frame gamma-ray light curves of GRBs without redshift, all observed by the Gamma-Ray Burst Monitor on the Fermi Gamma-Ray Space Telescope between 2008 and 2023.
We calculate the average power-density spectrum (PDS) of different GRB groups, categorized by fluence, peak rate, duration, redshift, and, for the first time, distinguish between the different GRB phases. We compare the resulting PDS profiles with their corresponding noise profiles, a comparison that has not been done previously. Our results reveal clear differences in the spectra of long and short bursts, precursor and prompt phases, and signal versus noise regions.
Previous studies have reported slopes consistent with a value of -5/3 Hz, associated with fully developed turbulence (Kolmogorov turbulence), suggesting that the gamma-rays in GRBs are produced by turbulent processes. Our analysis shows that almost all redshift-corrected spectra exhibit a power-law behavior with indices around -1.9 Hz. Notably, the precursor phase and redshift-corrected short bursts display a shallower power-law with indices of approximately -1.5 Hz. This indicates the presence of a different type of turbulence in some GRBs and phases.
