\begin{table}%T4 
\caption{\label{calib}Cross-calibration between the INTEGRAL high-energy instruments. A 
power-law model was fitted to the Crab (three upper rows) and Cen~A (three lower 
rows) spectra. The best-fit parameters for Crab are: a photon index $\Gamma$ of 
$2.19 \pm 0.01$ and a normalization at 1~keV of $17.1\pm 0.5$~photons~keV$^{-1}$~cm$^{-2}$~s$^{-1}$ with a reduced $\chi ^{2}$ of~1.71 for~49~degrees of freedom. 
The best-fit parameters for Cen~A: a photon index~$\Gamma$ of $1.80 \pm 0.01$ and 
a normalization at 1~keV of $0.153 \pm 0.006$~photons~keV$^{-1}$~cm$^{-2}$~s$^{-1}$ 
with a reduced $\chi ^{2}$ of~1.16 for 61 degrees of freedom. No systematic 
errors were added to the statistical ones.}
\small%\centering
\par
\begin{tabular}{cccc}
\hline\hline
Instrument & Exposure & Energy range & Rel. norm. \\
\multicolumn{1}{c}{} & [ks] & [keV] & \\
\hline
 ISGRI  & 1168 & 100--462 & 0.875 $\pm$ 0.003 \\
 SPI    & 910 & 105--957 & (1.00) \\
 PICsIT & 981 & 277--930 & 0.75 $\pm$ 0.01 \\
\hline
 ISGRI  & 771 & 19--462 & 0.89 $\pm$ 0.02 \\
 SPI    & 584 & 26--352 & (1.00) \\
 PICsIT & 429 & 277--454 & 0.85 $\pm $0.13 \\
\hline 
\end{tabular}   
\end{table}