The Unusual X‐Ray Spectrum of FU Orionis

FU Orionis stars (FUors) are young low-mass eruptive stars that are thoughtto be accreting at high rates. They could give rise to soft X-ray emission fromaccretion shocks, but their X-ray properties are largely unknown. We report thefirst X-ray detection of the prototype star FU Orionis with XMM-Newton. ItsX-ray spectrum is unusual compared to those of classical T Tauri stars (cTTS).The cool and hot components typically detected in cTTS are present but are seenthrough different absorption column densities. A heavily-absorbed hot componentat kT > 5 keV accounts for most of the observed flux and a strong Fe K emissionline is present. Such high temperatures are characteristic of magneticprocesses rather than shock emission. We discuss possible origins of theunusual spectrum in the context of a complex physical environment that likelyincludes disk accretion, a strong wind, magnetic activity, and close binarity.Comment: ApJ, vol. 643, in press. 23 pages, 4 figures, 1 tabl