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   71083
   From the recent ASCA observations, X-ray spectra of ultraluminous
   infrared galaxies (ULIRGs) are usually composed of two components; a
   hard non-thermal coponent which represents a dust-enshrouded AGN, plus
   a soft thermal component. If the latter is an emission from collisional
   ionization plasma, it resresents a nuclear starburst activity, and the
   enoumous far-infrared emission of ULIRGs is concluded to be powered by
   nuclear starbursts. On the other hand, if it is mainly comes from
   photoionized plasma, the AGN activity may be much larger than thought
   so far. We propose to observe two 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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