  The analyses of X-ray emission from classical novae during the outburst stage
have shown that the soft X-ray emission below 1 keV, which is thought to
originate from the photosphere of the white dwarf, is inconsistent with the
simple blackbody model of emission. Thus, $ROSAT$ Position Sensitive
Proportional Counter (PSPC) archival data of the classical novae GQ Mus 1983
(GQ Mus) have been reanalyzed in order to understand the spectral development
in the X-ray wavelengths during the outburst stage. The X-ray spectra are
fitted with the hot white dwarf atmosphere emission models developed for the
remnants of classical novae near the Eddington luminosity. The post-outburst
X-ray spectra of the remnant white dwarf is examined in the context of
evolution on the Hertzsprung-Russell diagram using C-O enhanced atmosphere
models. The data obtained in 1991 August (during the ROSAT All Sky Survey)
indicate that the effective temperature is kT_e<54 eV (<6.2x10^5 K). The 1992
February data show that the white dwarf had reached an effective temperature in
the range 38.3-43.3 eV (4.4-5.1x10^5 K) with an unabsorbed X-ray flux (i.e.,
$\sim$ bolometric flux) between 2.5x10^-9 and 2.3x10^-10 erg s^-1 cm^-2. We
show that the H burning at the surface of the WD had most likely ceased at the
time of the X-ray observations. Only the 1991 August data show evidence for
ongoing H burning.
