Power density spectra of gamma-ray bursts

Abstract

Power density spectra (PDSs) of long gamma-ray bursts (GRBs) provide useful information on GRBs, indicating their self-similar temporal structure. The best power-law PDSs are displayed by the longest bursts s) in which the range of self-similar timescales covers more than 2 decades. Shorter (T 90 ( 100 bursts have apparent PDS slopes more strongly aUected by statistical —uctuations. The underlying power law can then be reproduced with high accuracy by averaging the PDSs for a large sample of bursts. This power law has a slope aB (5/3 and a sharp break at D1 Hz. The power-law PDS provides a new sensitive tool for studies of GRBs. In particular, we calculate the PDSs of bright bursts in separate energy channels. The PDS —attens in the hard channel (h l( 300 keV) and steepens in the soft channel (h l 50 keV), while the PDS of bolometric light curves approximately follows the ( 5/3 law. We then study dim bursts and compare them to the bright ones. We —nd a strong correlation between the burst brightness and the PDS slope. This correlation shows that the bursts are far from being standard candles and dim bursts should be intrinsically weak. The time dilation of dim bursts is probably related to physi- cal processes occurring in the burst rather than to a cosmological redshift. Subject heading: gamma rays: bursts (ACF) in the separate channels and compare the results with previous studies of the ACF. In ∞ 6, we address dim GRBs and compare them to the bright ones. The results are discussed in ∞ 7.