X-ray properties of TDEs
  Observational astronomy of tidal disruption events (TDEs) began with the
detection of X-ray flares from quiescent galaxies during the ROSAT all-sky
survey of 1990-1991. The flares complied with theoretical expectations, having
high peak luminosities ($L_{\rm x}$ up to $\ge4\times 10^{44}$ erg/s), a
thermal spectrum with $kT\sim$few$\times10^5$ K, and a decline on timescales of
months to years, consistent with a diminishing return of stellar debris to a
black hole of mass $10^{6-8}$ solar masses. These measurements gave solid proof
that the nuclei of quiescent galaxies are habitually populated by a
super-massive black hole. Beginning in 2000, XMM-Newton, Chandra and Swift have
discovered further TDEs which have been monitored closely at multiple
wavelengths. A general picture has emerged of, initially near-Eddington
accretion, powering outflows of highly-ionised material, giving way to a calmer
sub-Eddington phase, where the flux decays monotonically, and finally a low
accretion rate phase with a harder X-ray spectrum indicative of the formation
of a disk corona. There are exceptions to this rule though which at the moment
are not well understood. A few bright X-ray TDEs have been discovered in
optical surveys but in general X-ray TDEs show little excess emission in the
optical band, at least at times coincident with the X-ray flare. X-ray TDEs are
powerful new probes of accretion physics down to the last stable orbit,
revealing the conditions necessary for launching jets and winds. Finally we see
that evidence is mounting for nuclear and non-nuclear intermediate mass black
holes based on TDE flares which are relatively hot and/or fast.
