  We present a Chandra observation of the recurrent nova U Scorpii, done with
the HRC-S detector and the LETG grating on day 18 after the observed visual
maximum of 2010, and compare it with XMM-Newton observations obtained in days
23 and 35 after maximum. The total absorbed flux was in the range 2.2-2.6 x
10^(-11) erg cm^(-2) s^(-1), corresponding to unabsorbed luminosity 7-8.5 x
10^(36)x(d/12 kpc)^2 for N(H)=2-2.7x10^(21) cm^(-2). On day 18, 70% of the soft
X-tray flux was in a continuum typical of a very hot white dwarf (WD)
atmosphere, which accounted for about 80% of the flux on days 23 and 35. In
addition all spectra display very broad emission lines, due to higher
ionization stages at later times.
  With Chandra we observed apparent P Cygni profiles. We find that these
peculiar profiles are not due to blue shifted absorption and red shifted
emission in photoionized ejecta, like the optical P Cyg of novae, but they are
rather a superposition of WD atmospheric absorption features reflected by the
already discovered Thomson scattering corona, and emission lines due to
collisional ionization in condensations in the ejecta. On days 23 and 35 the
absorption components were no longer measurable, having lost the initial large
blue shift that displaced them from the core of the broad emission lines. We
interpret this as indication that mass loss ceased between day 18 and day 23.
On day 35, the emission lines spectrum became very complex, with several
different components. Model atmospheres indicate that the WD atmospheric
temperature was about 730,000 K on day 18 and reached 900,000 K--one million K
on day 35. This peak temperature is consistent with a WD mass of at least 1.3
M(sol).
