Spectral Lags and Variability of Gamma-ray Bursts in the Swift Era
Open AccessGamma-ray bursts (GRBs) are thought to be the most concentrated and brightest explosions in the universe. Hence GRBs can be used to probe the early universe, including the re-ionization period as well as the intergalactic medium. GRBs may also be used to study the biggest mystery of our time: `Dark Energy'. However, GRBs as yet are not good standard candles. Hence, in order to use GRBs to connect luminosity and distance, we need GRB Luminosity Relations. One major limiting factor in GRB luminosity relation studies is the low statistics. Before the Swift mission there were very few GRBs with measured redshifts. But now in the Swift era we have more than 150 GRBs with measured redshifts. In this work we have utilized this high-quality data set to study two GRB luminosity relations.In Part-I we extracted spectral lags and studied the lag-luminosity relation. The spectral lag is the time difference between the arrival of high-energy and low-energy photons. To quantify this lag we have developed an improved method based upon the cross correlation function. With this method we investigated the lag-luminosity relation over the entire Swift Burst Alert Telescope (BAT) energy range. We also extended the relation to the source frame of the bursts.In Part-II we studied the variability of GRBs using Fourier analysis and introduce a new GRB luminosity relation. We extract a maximum frequency at which there is still significant signal power and associate this threshold frequency with the isotropic luminosity of the burst. As a result of this study, we propose a potential correlation between isotropic peak luminosity and the extracted threshold frequency.In Part-III we investigate long-term correlations and variability in GRB prompt emission light curves using the Hurst rescaled range analysis technique. As far as we know this is the first time this technique has been applied to GRBs. Based on this analysis, we present evidence indicating that the prompt emission of GRB light curves show anti-persistence.
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