A New Model for Iron Emission Lines and Re-Burst in GRB X-Ray Afterglows.pdf

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A New Model for Iron Emission Lines and Re-Burst in GRB X-Ray Afterglows.pdf

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A New Model for Iron Emission Lines and Re-Burst in GRB X-Ray Afterglows

a r X i v : a s t r o - p h / 0 5 0 4 5 3 3 v 2 2 9 A p r 2 0 0 5 A NEW MODEL FOR IRON EMISSION LINES AND RE-BURST IN GRB X-RAY AFTERGLOWS W.H.Gao and D.M.Wei Purple Mountain Observatory,Chinese Academy of Science,Nanjing,210008,China National Astronomical Observatories,Chinese Academy of Science,China ABSTRACT Recently iron emission features have been observed in several X-ray afterglows of GRBs. It is found that the energy obtained from the illuminating continuum which produces the emission lines is much higher than that of the main burst.The observation of SN-GRB association indicates a fallback disk should be formed after the supernovae explosion. The disk is optically thick and advection-dominated and dense. We suggest that the delayed injection energy after the initial main burst, much higher than energy of the main burst, causes the re-burst appearance in GRB afterglow and illuminates the region of the disk surface with τ ≈ 1(τ is the optical depth for the Thomson scatter ) and produces the iron emission line whose luminosity can be up to 10 45 ergs ?1 . The duration of the iron line emission can be 10 4 ? 10 5 s. This model can explain the appearance of re-burst and emission lines in GRB afterglow and disappearance of the iron emission lines, and also can naturally solve the problem of higher energy of the illuminating continuum than that of the main burst. This scenario is different from the models put forward to explain the emission lines before, that can be tested by SWIFT satellite. Subject headings: gamma rays:bursts-line:profiles-accretions disks-supernovae:general 1. Introduction Recently evidence is mounting that ’long duration’ GRBs are associated with a rare type of su- pernovae event such as a ’failed supernova’,’Hypernova’or ’Collapsar’( Woosley 1993; Paczyn?ski 1998; MacFadyen Woosley 1999; MacFadyen,Woosley and Herger 2001; Proga et al. 2003). In this model, the time between the supernovae explosion and the GRB is very short, nearly simul