An X-ray outburst from the rapidly accreting young star that illuminates McNeil's nebula

Young, low-mass stars are luminous X-ray sources1 whose powerful X-ray flares2,3,4,5,6 may exert a profound influence over the process of planet formation7. The origin of the X-ray emission is uncertain. Although many (or perhaps most) recently formed, low-mass stars emit X-rays as a consequence of solar-like coronal activity1,8,9, it has also been suggested that X-ray emission may be a direct result of mass accretion onto the forming star10,11,12. 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 at present undergoing a spectacular optical/infrared outburst13 (this star illuminates McNeil's nebula14). The outburst seems to be due to the sudden onset of a phase of rapid accretion13,15,16. The coincidence of a surge in X-ray brightness with the optical/infrared 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 flood of new material onto the star.