Research On Spectral Lag Properties Of Fermi Gamma-Ray Bursts

Broadband observations for gamma-ray bursts (GRBs) with GBM and LAT onboard Fermi satellite reveal some new temporal properties of the emission in the LAT band with respect to that in the GBM band. In this paper, we mainly focus on the spectral lag patterns of GeV emission and Energy dependence of the spectral lag in the GBM band.In the fisrt part of this paper, we review the history of gamma-ray bursts study, including progress we have made in GRB field in past decades and its observational properties and basic theoretical scenario. We also provide a brief summary of the Fermi mission, focusing on two instruments onbord Fermi and progress relevant to gamma-ray bursts study made by Fermi.We describe our work on spectral lag in the second part. The background of spectral lag study, the method used to calculate spectral lag and its uncertainty is also described. Our work contains following aspects:1) whether GeV component will lag behind MeV component in a individual pulse;2) energy dependence of spectral lag;3) whether there is relationship between the spectral lag and Ep evolution pattern;4) energy dependences of the spectral lag in the rising and decaying phases;5) spectral lag properties in multiple pulses GRBs;6) examine the Lag-Luminosity relation using14z-known GRBs in our sample.According to our study, we conclude that:1) With respect to the associated pulses in the low-E bands, the high-E emission does not lag behind the low-E emission.2) Both in Hard-to-soft and Flux Tracking pulses spectral lag relative to the softest band become lager with energy band increase.3) No obvious relation between the spectral lag (or differential spectral lag) and Ep evolution feature is found though we prove that spectral evolution can generate spectral lag.4) The energy dependences of the spectral lag in the rising and ecaying phases are opposite for some Flux Tracking GRBs.5) In the Lag-Luminosity relation represented by us, A trend that brighter GRBs tend to have a smaller spectral lag is still observed, however, the scatter is getting much larger than previous results.