An X-ray Outburst from the Rapidly Accreting Young Star That Illuminates   McNeil's Nebula
  Young, low-mass stars are luminous X-ray sources whose powerful X-ray flares may exert a profound influence over the process of planet formation. The origin of such emission is uncertain. Although many or perhaps most recently formed, low-mass stars emit X-rays as a consequence of solar-like coronal activity, it has also been suggested that X-ray emission may be a direct result of mass accretion onto the forming star. Here we report X-ray imaging spectroscopy observations which reveal a factor ~50 increase in the X-ray flux from a young star that is presently undergoing a spectacular optical/IR outburst. The outburst is thought to be due to the sudden onset of a phase of rapid accretion. The coincidence of a surge in X-ray brightness with the optical/IR eruption demonstrates that strongly enhanced high-energy emission from young stars can occur as a consequence of high accretion rates. We suggest that such accretion- enhanced X-ray emission from erupting young stars may be short-lived, because intense star-disk magnetospheric interactions are quenched rapidly by the subsequent accretion flood. 
J.H. Kastner (1), M. Richmond (1), N. Grosso (2), D.A. Weintraub (3),   T. Simon (4), A. Frank (5), K. Hamaguchi (6), H. Oza...