  We study optical and X-ray properties of the ultraluminous IRAS galaxy
10026+4347. This galaxy is a narrow-line QSO with very strong FeII emission.
Three optical spectra were taken over two years. The full widths at half
maximum (FWHMs) of the emission lines are constant whereas the third spectrum
seems to show a continuum change. Intermediate-band photometry also shows a
small (0.1 mag) but significant decrease in flux. HST WFPC2 images suggest that
this object is a post-merger galaxy. The source is X-ray luminous (L_x ~ 10^45
erg/s) with a very soft X-ray spectrum (photon index ~ 3.2) The X-ray
luminosity exhibits variabilities of a factor of ~8 over four years and a
factor of two within two days. During these X-ray flux changes, the X-ray
spectral shapes are consistent with no variation. All the optical and X-ray
properties resemble those of narrow-line Seyfert 1 galaxies, except that the
FWHM of Hbeta is about 2500 km/s, larger than that for most NLS1s. We discuss
the implications of our results on models of NLS1s.
