X-ray view of V1647 Ori, the young star in outburst illuminating McNeil's Nebula


McNeil's Nebula was discovered serendipitously in January 2004 in the L1630 dark cloud located in the Orion B giant molecular cloud. This reflection nebula is illuminated by V1647 Ori, a young stellar object displaying since November 2003 a dramatic optical/IR outburst, which is the origin of the rise of this fan-shaped nebula. Until recently, no X-ray satellites have had the opportunity to observe this kind of pre-main sequence eruptive object at the beginning of its accretion burst. In this respect the X-ray observations of V1647 Ori obtained in 2004 with Chandra (Kastner et al. 2004) and XMM-Newton (Grosso et al. 2005) offer new insight into pre-main sequence accretion processes. I will review these X-ray observations, which reveal a large increase of the X-ray emission compared to the pre-outburst state, and an enhanced X-ray variability. The analysis of the XMM-Newton spectra shows that about 75% of the intrinsic X-ray emission in the 0.5-8 keV energy band comes from a soft plasma component, reminiscent of the X-ray spectrum of the classical T Tauri star TW Hya, for which X-ray emission is believed to be generated by an accretion shock onto the photosphere of a low-mass star. The hard plasma component contributes about 25% of the total X-ray emission, and can be understood only in the framework of plasma heating sustained by magnetic reconnection events. A significant excess of hydrogen column density is found compared to the value derived from optical/IR observations, suggesting either that there is a real excess of gas column density - which might due to an intervening outflow unveiled from ground optical spectroscopy - or that optical/IR observations do not probe the extinction down to the star itself. I will present preliminary results of the XMM-Newton observation of V1647 Ori obtained in March 2005

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This paper was published in Hal - Université Grenoble Alpes.

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