The Spectacular X-ray Tidal Disruption Event AT2021ehb

At 78Mpc, AT2021ehb is the third closest tidal disruption event (TDE) discovered by optical sky surveys. With a peak X-ray flux of 1mCrab, it is brighter than all other non-jetted TDEs in the X-ray sky. In this talk, I will present the comprehensive X-ray (NuSTAR, Swift/XRT, NICER, XMM-Newton, SRG/eROSITA), UV (Swift/UVOT), and optical (ZTF/Keck) observations of AT2021ehb. We find (1) a soft --> hard --> soft X-ray spectral transition, which has never been seen in a TDE before; (2) the bolometric luminosity peaks (~0.05Ledd) when the corona (hard X-ray) emission is the strongest, which is different from other accreting black hole systems; (3) the detection of an ultra-fast outflow (v>0.1c) in multiple X-ray spectra; (4) a surprisingly flat UV/optical light curve during the drastic X-ray evolution. I will comment on how these observations can help us understand the interplay between the accretion disk, the hot corona, and the outflow.