XMM-Newton observations of the BL Lac MS 0737+7441

We report on the XMM-Newton observations of the BL Lac object MS 0737.9+7441 during the performance verification phase. A simple power-law fit provides an adequate description of the integrated spectrum in the 0.2-10 keV energy band. The photon index is slightly steeper in the EPIC pn data with $\Gamma = (2.38 \pm 0.01)$ compared to the EPIC MOS data ( $\Gamma = (2.28 \pm 0.01)$). The difference is most probably due to the present uncertainties in the calibration of the EPIC MOS and EPIC pn data sets. We report evidence for intrinsic absorption in the distant BL Lac above the Galactic column ( $N_{\rm H, Gal} = 3.2 10^{20} \rm {cm^{-2}}$) which is $N_{\rm H, fit}^{z=0.315} = (2.70 \pm 0.20) 10^{20} {\rm cm}^{-2}$ in the EPIC pn data and $N_{\rm H, fit}^{z=0.315} = (3.25 \pm 0.25) 10^{20} {\rm cm}^{-2}$ in the EPIC MOS data assuming neutral gas and solar abundances. The flux variations are found to be of the order of 10% . No significant spectral variability is detected.