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   61091
   From the recent ASCA observations, X-ray spectra of ultraluminous
   infrared galaxies (ULIRGs) are usually composed of two components; a
   hard non-thermal component which resresents a dust-enshrouded AGN, plus
   a soft thermal component. If the latter is an emission from collisional
   ionization plasma, it represents a nuclear starburst activity, and the
   enormous far-infrared emission of ULIRGs is powered by nuclear
   starbursts. On the other hand, if it is mainly comes from photoionized
   plasma, the AGN activity may be much larger than previously thought. We
   propose to observe three nearby infrared-luminous starburst galaxies,
   to study the origin of the soft thermal component of ULIRGs, which will
   let us reveal the mystery of the power source of ULIRGs.
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