**Table 4:** Mean parameters of each sub-sample from this paper. We include the decay index ( $\delta$ ), the spectral index ( $\alpha$ ), the flux at 11 h after the burst and the observation start time. We also recall the main parameters from the BeppoSAX sample (De Pasquale et al. 2006). All errors are quoted at a 68% confidence level.
	Chandra	Chandra	XMM	BeppoSAX
	Imaging	Grating
$\delta$	$2.0 \pm 0.3$	$1.4 \pm 0.1$	$1.2 \pm 0.2$	$1.3 \pm 0.1$
$\alpha$	$0.8 \pm 0.1$	$1.0 \pm 0.1$	$1.2 \pm 0.2$	$1.2 \pm 0.1$
Log(Flux)	$-11.6 \pm 0.3$	$-11.8 \pm 0.3$	$-12.6 \pm 0.2$	$-12.2 \pm 0.1$
@ 11 h
Obs. time	145.4	95.9	30.1	36.5
(ksec)

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