TY - JOUR
T1 - The gamma-ray burst 050904
T2 - Evidence for a termination shock?
AU - Gendre, B.
AU - Galli, A.
AU - Corsi, A.
AU - Klotz, A.
AU - Pire, L.
AU - Stratta, G.
AU - Boër, M.
AU - Damerdji, Y.
PY - 2007/2
Y1 - 2007/2
N2 - 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.
AB - 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.
KW - Gamma rays: bursts
KW - X-rays: general
UR - http://www.scopus.com/inward/record.url?scp=33846813897&partnerID=8YFLogxK
U2 - 10.1051/0004-6361:20065220
DO - 10.1051/0004-6361:20065220
M3 - Article
AN - SCOPUS:33846813897
SN - 0004-6361
VL - 462
SP - 565
EP - 573
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
IS - 2
ER -