XMM-Newton X-ray observations of the Carina nebula

We use new XMM-Newton observations to perform a detailed X-ray analysis of the Carina nebula region in the 0.3-12 keV energy range. Our source detection yields 80 discrete Xray sources, from which about 20 per cent seem not to have optical counterparts. To get an idea of the energy spectrum of these sources, we construct an X-ray colour-colour diagram using the energy bands 0.3-2, 2-4.5 and 4.5-12 keV. We analyse the spectra of the most intense X-ray sources associated with early-type stars, including the luminous blue variable eta Carina and WR25. We show that the X-ray emission from these sources is well fitted by multitemperature model spectra. We detect surprisingly intense X-ray emission at energies above 4 keV for some of the observed early-type stars, especially from CPD-59 2629 (Tr16-22) which presents particularly hard X-ray emission. We detect intense soft X-ray emission, below < 2 keV, in HDE 303311, which presents an X-ray excess of about 100 times higher than has been observed in other O5V stars. We use these data to construct the L-x/L-bol relation for the 0.3-12 and 3.0-12 keV energy ranges, for all the observed O-type stars, plus eta Carina and WR25. Most of the bright stars seem to agree with low metallicity spectral models. The L-x/L-bol ratio for O-type stars in the 0.3-12 keV range is well fitted by a constant approximate to 6.0(4.8)(75) x 4 8 x 10(-7), in fair agreement with the canonical expression L-x/L-bol similar to 2 x 10(-7) formerly estimated for the 0.3-2.4 keV energy band. In contrast, the L-x/L-bol relation for the 3.0-12 keV range presents a strong deviation from the canonical relation, with a high dispersion of about four orders of magnitude. We also detect intrinsic X-ray time variability in seven sources, over the time-scale of about 50 h covered by the observations. This includes an X-ray flare of about 2-h duration detected in DETWC Tr16 J104429.2-594143, a source probably not physically associated with the Carina nebula. We discuss the different underlying physical mechanisms that can be responsible for the X-ray emission from early-type stars.