The exceptionally extended flaring activity in the X-ray afterglow of GRB 050730 observed with Swift and XMM-Newton
Perri, M. ; Guetta, D. ; Antonelli, L. A. ; ...Giommi, P. ; et al.
Aug - 2007
ISSN : 0004-6361 ;
journal : Astronomy and Astrophysics

Issue : 1
type: Article Journal

Abstract
We present the results of a detailed spectral and temporal analysis of Swift and XMM-Newton observations of the high redshift (z=3.969) GRB 050730. The X-ray afterglow of GRB 050730 was found to decline with time with superimposed intense flaring activity that extended over more than two orders of magnitude in time. Seven distinct re-brightening events starting from 236 s up to 41.2 ks after the burst were observed. The underlying decay of the afterglow was well described by a double broken power-law model with breaks at t\_1= 237 +/- 20 s and t\_2 = 10.1 (-2.2) (+4.6) ks. The temporal decay slopes before, between and after these breaks were alpha\_1 = 2.1 +/- 0.3, alpha\_2 = 0.44 (-0.08) (+0.14) and alpha\_3 = 2.40 (+0.07) (-0.09), respectively. The spectrum of the X-ray afterglow was well described by a photoelectrically absorbed power-law with an absorbing column density N\_H=(1.28 +/- 0.26) 10\^22 cm\^-2 in the host galaxy. Strong X-ray spectral evolution during the flaring activity was present. In the majority of the flares (6/7) the ratio Delta\_t/t\_p between the duration of the event and the time when the flare peaks was nearly constant and about 0.6-0.7. We showed that the observed spectral and temporal properties of the first three flares are consistent with being due both to high-latitude emission, as expected if the flares were produced by late internal shocks, or to refreshed shocks, i.e. late time energy injections into the main afterglow shock by slow moving shells ejected from the central engine during the prompt phase. The event fully satisfies the E\_p-E\_iso Amati relation while is not consistent with the E\_p-E\_jet Ghirlanda relation.

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