All Figures

$\begin{figure} \par\includegraphics[width=8cm,clip]{4085fig1.ps}\end{figure}$ Figure 1: Light curves in terms of observed fluxes versus observed time since the burst trigger for the 24 GRBs reported in Table 1. Fluxes have been corrected only for the galactic extinction. The references for all the plotted data are given in the appendix.
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In the text

$\begin{figure} \par\includegraphics[width=5.5cm,clip]{4085fig2.ps}\end{figure}$ Figure 2: Histogram of the observed fluxes (in mJy) in the R-band (Cousin system) 12 h after the trigger (observer frame - from Fig. 1). All fluxes have been corrected for the foreground galactic extinction only. Superimposed to the histogram is a Gaussian fit to the data with mean value $\mu =-1.03$ and dispersion $\sigma =0.48$ . Note that the fit is rather poor and most likely underestimates the real width of the distribution.
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In the text

$\begin{figure} \par\includegraphics[width=5.5cm,clip]{4085fig3.ps}\end{figure}$ Figure 3: Histogram of the host absorption values $A_{V}^{\rm host}$ for the 24 GRBs of Table 1. The 9 GRBs in the first bin have an optical spectrum consistent with a null host-galaxy absorption.
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In the text

$\begin{figure} \par\includegraphics[width=16.35cm,clip]{4085fig4.ps}\end{figure}$ Figure 4: Light curves of the optical luminosities as a function of the rest-frame time. The three underluminous GRBs are labelled. All data have been corrected for extinction (both Galactic and host). The references for the observed magnitudes can be found in the appendix. The references for the values of the spectral index $\beta$ and the host galaxy absorption can be found in the footnote of Table 1.
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In the text

$\begin{figure} \par\includegraphics[width=6.8cm,clip]{4085fig5.ps}\end{figure}$ Figure 5: Histogram of the monochromatic optical luminosities 12 h (rest frame) after the trigger for the 24 GRBs reported in Table 1 and shown in Fig. 4. Data have been dereddened both for Galactic and host extinction. The solid red line represents the Gaussian fit to the data with mean value $\mu =30.65$ and dispersion $\sigma =0.28$ .
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In the text

$\begin{figure} \par\includegraphics[width=6.8cm,clip]{4085fig6.ps}\end{figure}$ Figure 6: Histogram of the X-ray luminosities 12 h (rest frame) after the trigger, calculated in the rest frame band [4-20 keV].
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{4085fig7.ps}\end{figure}$ Figure 7: X-ray monochromatic [2 keV, rest frame] luminosity as a function of the optical monochromatic [R band, rest frame] luminosity at 12 h after trigger. The dashed lines correspond to different broad-band spectral indices $\beta _{\rm RX}$ as labelled.
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In the text

$\begin{figure} \par\includegraphics[width=8.1cm,clip]{4085fig8.ps}\end{figure}$ Figure 8: Optical monochromatic luminosity ( top panel) and X-ray [4-20 keV] luminosities ( mid panel) at 12 h after trigger (rest frame time) as a function of the isotropic emitted energy during the prompt phase (integrated between 1 keV and 10 MeV, see Ghirlanda et al. 2004). Circles correspond to bursts having both optical and X-ray data. Triangles are GRBs with optical but no X-ray data. Stars are the two GRBs (as labelled) with X-rays but no optical data. We also show GRB 970228, for which there is no information on the amount of extinction in the host (square). The dashed line is the linear regression fit ( $\log L_{\rm x} \propto 0.51 \log E_{\gamma, \rm iso}$ ), which has a chance probability $P=3\times 10^{-3}$ .
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In the text

$\begin{figure} \par\includegraphics[width=8.4cm,clip]{4085fig9.ps}\end{figure}$ Figure 9: For those bursts of measured $\theta _{\rm j}$ , we have calculated the collimation corrected afterglow luminosity ( top panel: optical; bottom panel: X-ray) at 12 h after trigger (rest-frame time) as a function of the collimation-corrected emitted energy during the prompt phase (integrated between 1 keV and 10 MeV, see Ghirlanda et al. 2004). Symbols as in Fig. 8. There is now no correlation between the optical or the X-ray luminosity and the prompt emitted energy.
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In the text

$\begin{figure} \par\includegraphics[width=11.5cm,clip]{4085fig10.ps}\end{figure}$ Figure 10: Optical to X-ray spectral energy distribution for all GRBs in our sample. Data are simultaneous, at the rest-frame time labelled in each panel. Sources of data: GRB 970228: optical: Reichart (1999); X-rays: Costa et al. (1997). GRB 970508: Galama et al. (1998); Piro et al. (1998). GRB 971214: Wijers et al. (1999); Stratta et al. (2004). GRB 980613: Hjorth et al. (2002); Costa (1999). GRB 980703: Vreeswijk et al. (1999); De Pasquale et al. (2003). GRB 990123: Galama et al. (1999); Heise et al. (1999). GRB 990510: optical: Harrison et al. (1999); X-rays: Gendre & Boër (2005). GRB 991216: Halpern et al. (2000), Garnavich et al. (2000); Piro et al. (2000). GRB 000210: Piro et al. (2002). GRB 000214: Antonelli et al. (2000). GRB 000301c: Jensen et al. (2001). GRB 000418: Klose et al. (2000). GRB 000911: Masetti et al. (2005). GRB 000926: optical: Fynbo et al. (2001). X-rays: Gendre & Boër (2005). GRB 010222: optical: Masetti et al. (2001). X-rays: Gendre & Boër (2005).
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In the text

$\begin{figure} \par\includegraphics[width=11.5cm,clip]{4085fig11.ps}\end{figure}$ Figure 11: Optical to X-ray spectral energy distribution for all GRBs in our sample. Data are simultaneous, at the rest-frame time labelled in each panel. Sources of data: GRB 010921: Price et al. (2002). GRB 011121: optical: Garnavich et al. (2003); X-rays: Gendre & Boër (2005). GRB 020124: Hjorth et al. (2003). GRB 020405: Masetti et al. (2003); Mirabal et al. (2003). GRB 020813: optical: Covino et al. (2003); X-rays: Butler et al. (2003). GRB 021004: optical: Pandey et al. (2003); X-rays: Butler et al. (2003). GRB 021211: Nysewander et al. (2005). GRB 030323: Vreeswijk et al. (2004). GRB 030226: optical: Pandey et al. (2004); X-rays: Gendre & Boër (2005). GRB 030329: optical: Bloom et al. (2004); Matheson et al. (2003); X-rays: Gendre & Boër (2005). GRB 030429: Jakobsson et al. (2004).
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{4085fig12.eps}\end{figure}$ Figure 12: Superposed light curves of the optical luminosities in the rest frame of the 14 GRBs detected by SWIFT with enough photometric data to the light curves already shown in Fig. 4 (grey dots). The luminosities of all SWIFT GRBs are corrected only for the galactic absorption, except for GRB 050401, for which $A_V^{\rm host}=0.67$ (Watson et al. 2005), GRB 050525, for which $A_V^{\rm host}=0.25$ $\pm$ 0.15 (Blustin et al. 2005) and GRB 050730 for which $A_V^{\rm host}\sim 0$ (Starling et al. 2005). The SWIFT GRBs luminosities have been k-corrected assuming a common spectral index $\beta =1$ . The names of the SWIFT GRBs are given near their light curves.
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{4085fig13.eps}\end{figure}$ Figure 13: Like Fig. 5 with added, the monochromatic optical luminosities 12 h (rest frame) after the trigger of the 14 GRBs discovered by SWIFT whose intrinsic luminosities could be calculated from the photometric data. We caution the reader that the optical luminosities of all SWI bursts (except GRB 050401, GRB 050525 and GRB 050730) are uncorrected for the host galaxy absorption and are k-corrected assuming a the same optical spectral index ( $\beta =1$ ) for all bursts (except GRB 050401, GRB 0505025 and GRB 050730).
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In the text

$\begin{figure} \par\includegraphics[width=6.8cm,clip]{4085fig14.ps}\end{figure}$ Figure 14: Like Fig. 6, the X-ray [4-20 keV] luminosities 12 h (rest frame) after the trigger of the 11 GRBs discovered by SWIFT whose intrinsic luminosities could be calculated from the data found in Nousek et al. (2005; for GRB 050730, see Perri et al. 2005; for GRB 050820, see Page et al. 2005).
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In the text

$\begin{figure} \par\includegraphics[width=7cm,clip]{4085fig15.ps}\end{figure}$ Figure 15: Examples of spectra calculated using the prescriptions of Panaitescu & Kumar (2000), at 12 h after trigger. Dashed lines correspond to a homogeneous ISM case (with density n=1 cm^-3); solid lines to a wind profile of the density (with $\dot M=3$ $\times$ $10^{-6}~M_\odot$ yr^-1and wind velocity v=10³ km s^-1. The models differ for the assumed values of p (as labelled).
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In the text

$\begin{figure} \par\includegraphics[width=8cm,clip]{4085fig1.ps}\end{figure}$	Figure 1: Light curves in terms of observed fluxes versus observed time since the burst trigger for the 24 GRBs reported in Table 1. Fluxes have been corrected only for the galactic extinction. The references for all the plotted data are given in the appendix.
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$\begin{figure} \par\includegraphics[width=5.5cm,clip]{4085fig3.ps}\end{figure}$	Figure 3: Histogram of the host absorption values $A_{V}^{\rm host}$ for the 24 GRBs of Table 1. The 9 GRBs in the first bin have an optical spectrum consistent with a null host-galaxy absorption.
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$\begin{figure} \par\includegraphics[width=6.8cm,clip]{4085fig5.ps}\end{figure}$	Figure 5: Histogram of the monochromatic optical luminosities 12 h (rest frame) after the trigger for the 24 GRBs reported in Table 1 and shown in Fig. 4. Data have been dereddened both for Galactic and host extinction. The solid red line represents the Gaussian fit to the data with mean value $\mu =30.65$ and dispersion $\sigma =0.28$ .
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$\begin{figure} \par\includegraphics[width=6.8cm,clip]{4085fig6.ps}\end{figure}$	Figure 6: Histogram of the X-ray luminosities 12 h (rest frame) after the trigger, calculated in the rest frame band [4-20 keV].
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$\begin{figure} \par\includegraphics[width=8cm,clip]{4085fig7.ps}\end{figure}$	Figure 7: X-ray monochromatic [2 keV, rest frame] luminosity as a function of the optical monochromatic [R band, rest frame] luminosity at 12 h after trigger. The dashed lines correspond to different broad-band spectral indices $\beta _{\rm RX}$ as labelled.
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$\begin{figure} \par\includegraphics[width=6.8cm,clip]{4085fig14.ps}\end{figure}$	Figure 14: Like Fig. 6, the X-ray [4-20 keV] luminosities 12 h (rest frame) after the trigger of the 11 GRBs discovered by SWIFT whose intrinsic luminosities could be calculated from the data found in Nousek et al. (2005; for GRB 050730, see Perri et al. 2005; for GRB 050820, see Page et al. 2005).
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$\begin{figure} \par\includegraphics[width=7cm,clip]{4085fig15.ps}\end{figure}$	Figure 15: Examples of spectra calculated using the prescriptions of Panaitescu & Kumar (2000), at 12 h after trigger. Dashed lines correspond to a homogeneous ISM case (with density n=1 cm^-3); solid lines to a wind profile of the density (with $\dot M=3$ $\times$ $10^{-6}~M_\odot$ yr^-1and wind velocity v=10³ km s^-1. The models differ for the assumed values of p (as labelled).
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