The gamma-ray burst 050904: Evidence for a termination shock?

B. Gendre, A. Galli, A. Corsi, A. Klotz, L. Pire, G. Stratta, M. Boër, Y. Damerdji

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Abstract

Aims. We analyze optical and X-ray observations of GRB 050904 obtained with TAROT and SWIFT. Methods. We perform temporal and spectral analysis of the X-ray and optical data. Results. We find significant absorption in the early phase of the X-ray light curve, with some evidence (3σ level) of variability. We interpret this as a progressive photo-ionization. We investigate the environment of the burst and constrain its density profile. We find that the overall behavior of the afterglow is compatible with a fireball expanding in a wind environment during the first 2000 s after the burst (observer frame). On the other hand, the late (after 0.5 days, observer frame) afterglow is consistent with an interstellar medium, suggesting the possible presence of a termination shock. We estimate the termination shock position to be R t ∼ 1.8 × 10-2 pc, and the wind density parameter to be A* ∼ 1.8. We try to explain the simultaneous flares observed in optical and X-ray bands in light of different models: delayed external shock from a thick shell, inverse Compton emission from reverse shock, inverse Compton emission from late internal shocks or a very long internal shock activity. Among these models, those based on a single emission mechanism, are unable to account for the broad-band observations. Models invoking late internal shocks, with the inclusion of IC emission, or a properly tuned very long internal shock activity, offer possible explanations.

Original languageEnglish
Pages (from-to)565-573
Number of pages9
JournalAstronomy and Astrophysics
Volume462
Issue number2
DOIs
StatePublished - Feb 2007

Keywords

  • Gamma rays: bursts
  • X-rays: general

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    Gendre, B., Galli, A., Corsi, A., Klotz, A., Pire, L., Stratta, G., Boër, M., & Damerdji, Y. (2007). The gamma-ray burst 050904: Evidence for a termination shock? Astronomy and Astrophysics, 462(2), 565-573. https://doi.org/10.1051/0004-6361:20065220