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Swift and XMM-Newton observations of the extraordinary gamma-ray burst 060729: More than 125 days of x-ray afterglow

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posted on 24.10.2012, 09:06 by D Grupe, C Gronwall, X-Y Wang, PWA Roming, J Cummings, B Zhang, P Meszaros, MD Trigo, PT O'Brien, KL Page, A Beardmore, O Godet, vanden Berk DE, PJ Brown, S Koch, D Morris, M Stroh, DN Burrows, JA Nousek, MM Chester, S Immler, V Mangano, P Romano, G Chincarini, J Osborne, T Sakamoto, N Gehrels
We report the results of the Swift andXMM-Newton observations of the Swift -discovered GRB 060729 (T90 = 115 s). The afterglow of this burst was exceptionally bright in X-rays as well as at UV/optical wavelengths, showing an unusually long slow decay phase ( Alpha = 0.14 +/- 0.02), suggesting a larger energy injection phase at early times than in other bursts. The X-ray light curve displays a break at about 60 ks after the burst. The X-ray decay slope after the break is Alpha = 1.29 +/- 0.03. Up to 125 days after the burst we do not detect a jet break, suggesting that the jet opening angle is larger than 28 degrees. We find that the X-ray spectra of the early phase change dramatically and can all be fitted by an absorbed singleYpower-law models or alternatively by a blackbody plus power-law model. The power-law fits show that the X-ray spectrum becomes steeper while the absorption column density decreases. In the blackbody model the temperature decreases from kT = 0.6 to 0.1 keV between 85 and 160 s after the burst in the rest frame. The afterglow was clearly detected up to 9 days after the burst in all six UVOT filters and in UVW1 even for 31 days. A break at about 50 ks is clearly detected in all six UVOT filters from a shallow decay slope of about 0.3 and a steeper decay slope of 1.3.The XMM-Newton observations started about 12 hr after the burst and show a typical afterglow X-ray spectrum with Beta[SUBSCRIPT x] = 1.1 and absorption column density of 1 x 10^21 cm^-2



Astrophysical Journal, 2007, 662 (1), pp. 443-458

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American Astronomical Society, IOP Publishing



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