All Figures

$\begin{figure} \par\includegraphics[width=15.5cm,clip]{5173fig1.ps}\end{figure}$ Figure 1: The 0.2-10 keV light curve of GRB 050904 as observed by the BAT and XRT. The observed BAT count rates were extrapolated into the XRT 0.2-10 keV band using a conversion factor evaluated from the BAT best fit spectral model (Table 1). The observed XRT count rates were converted into flux $F_{0.2-10~{\rm keV}}$ (scale on the right side) using the best fit spectral parameters listed in Table 1. The equivalent isotropic luminosity (scale on the left side) was calculated as $F_{0.2-10~{\rm keV}}$ 4 $\pi$ d_L² $(1+z)^{(\Gamma -2)}$ where d_L is the luminosity distance and the last term is the K correction factor for emission modeled by a power law. The error bars are given by the quadrature sum of the count rate statistical error and the estimated uncertainties in the conversion factors. The inset shows BAT and XRT $F_{0.2-10~{\rm keV}}$ for the first orbit and the best fit model for XRT data. Note that small differences in the the burst history shown in the inset ( $F_{0.2-10~{\rm keV}}$ units) and the main picture, which shows the evolution in luminosity units, are due to the photon index dependence in the K correction factor and its measurement in discrete time intervals.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{5173fig2.ps}\end{figure}$ Figure 2: Hardness ratio evolution of GRB 050904. The top and middle panels show the count rate evolution of XRT data in two different energy bands in the rest frame.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{5173fig3.ps}\end{figure}$ Figure 3: Spectral evolution of GRB 050904. The top panel illustrates how the photon index $\Gamma$ of GRB 050904 changes during the observation. In the bottom panel the burst evolution is plotted to show how the time intervals for spectral analysis were selected. Vertical bars indicate the time intervals selected for BAT and XRT spectral analysis whose results are reported in Table 2 and Fig. 4.
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In the text

$\begin{figure} \par\includegraphics[angle=-90,width=8cm,clip]{5173fig4.ps}\end{figure}$ Figure 4: Spectral evolution of GRB 050904; BAT and XRT E²F(E) spectra (equivalent to $\nu$ F( $\nu$ ) spectra) deconvolved from the detector response for five selected time intervals (see bottom panel in Fig. 3).
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In the text

$\begin{figure} \par\includegraphics[angle=-90,width=8cm,clip]{5173fig5.ps}\end{figure}$ Figure 5: GRB 050904 light curves in the 0.2-10 keV band as they would be observed if the burst were located at different redshifts. Each light curve includes both BAT and XRT extrapolations. The horizontal line gives an indication of the sensitivity limit of BAT, while the vertical line marks the start of the XRT follow-up in the observing frame.
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{5173fig6.ps}\end{figure}$ Figure 6: The K-corrected 0.2-10 keV time histories of the high-redshift ( ${\protect \ga}$ 4) GRBs observed by Swift. Each light curve includes both XRT and BAT data extrapolated to the XRT energy range. The K correction was performed for an average photon index for simplicity.
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In the text

$\begin{figure} \par\includegraphics[width=8.5cm,clip]{5173fig2.ps}\end{figure}$	Figure 2: Hardness ratio evolution of GRB 050904. The top and middle panels show the count rate evolution of XRT data in two different energy bands in the rest frame.
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$\begin{figure} \par\includegraphics[angle=-90,width=8cm,clip]{5173fig4.ps}\end{figure}$	Figure 4: Spectral evolution of GRB 050904; BAT and XRT E²F(E) spectra (equivalent to $\nu$ F( $\nu$ ) spectra) deconvolved from the detector response for five selected time intervals (see bottom panel in Fig. 3).
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$\begin{figure} \par\includegraphics[angle=-90,width=8cm,clip]{5173fig5.ps}\end{figure}$	Figure 5: GRB 050904 light curves in the 0.2-10 keV band as they would be observed if the burst were located at different redshifts. Each light curve includes both BAT and XRT extrapolations. The horizontal line gives an indication of the sensitivity limit of BAT, while the vertical line marks the start of the XRT follow-up in the observing frame.
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$\begin{figure} \par\includegraphics[width=8cm,clip]{5173fig6.ps}\end{figure}$	Figure 6: The K-corrected 0.2-10 keV time histories of the high-redshift ( ${\protect \ga}$ 4) GRBs observed by Swift. Each light curve includes both XRT and BAT data extrapolated to the XRT energy range. The K correction was performed for an average photon index for simplicity.
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