| תקציר: | Ultra-luminous x-ray sources are an enigma. Their apparent luminosity
exceeds the Eddington limit for the most massive stellar mass black hole
predicted by stellar evolution theory and thus they are either more
massive than 20 solar masses or, somehow, exceed the Eddington limit.
They have a unique set of x-ray spectral and temporal properties
different from possible stellar mass or active galaxy analogs. Their
optical counterparts are very faint and do not show obvious unusual
photometric signatures. I will discuss recent observations of the x-ray
spectral and timing behaviors of ULXs and their UV and radio properties. |