A Comprehensive Analysis of Insight-HXMT Gamma-Ray Burst Data. I. Power Density Spectrum

The power density spectrum (PDS) is a powerful tool to study light curves of gamma-ray bursts (GRBs). We show the average PDS and individual PDS analysis with GRB data from the Hard X-ray Modulation Telescope (also named Insight-HXMT). The values of the power-law index of the average PDS ( ${\alpha }_{\bar{P}}$ ) for long GRBs (LGRBs) vary from 1.58 to 1.29 (for 100–245, 245–600, and 600–2000 keV). The Insight-HXMT data allow us to extend the energy of the LGRBs up to 2000 keV, and a relation between ${\alpha }_{\bar{P}}$ and energy E is obtained: ${\alpha }_{\bar{P}}\propto {E}^{-0.09}$ (8–2000 keV). We first systematically investigate the average PDS and individual PDSs for short GRBs (SGRBs), and obtain ${\alpha }_{\bar{P}}\propto {E}^{-0.07}$ (8–1000 keV), where the values of ${\alpha }_{\bar{P}}$ vary from 1.86 to 1.34. The distribution of the power-law index of an individual PDS ( α ) of an SGRB is consistent with that of an LGRB, and the α value for the group with a dominant timescale (the bent power law) is higher than that for the group with no dominant timescale (the single power law). Both LGRBs and SGRBs show similar α and ${\alpha }_{\bar{P}}$ , which indicates that they may be the result of similar stochastic processes. Typical values of the dominant timescale τ for LGRBs and SGRBs are 1.58 s and 0.02 s, respectively. It seems that τ varies in proportion to the duration of GRBs T _90 , with a relation $\tau \propto {T}_{90}^{0.86}$ . The GRB light curve may result from superposing a number of pulses with different timescales. No periodic or quasi-periodic signal above the 3 σ significance threshold is found in our sample.