  We present an analysis of X-ray and UV data obtained with the XMM-Newton
Observatory of the long period dwarf nova RU Peg. RU Peg contains a massive
white dwarf, possibly the hottest white dwarf in a dwarf nova, it has a low
inclination, thus optimally exposing its X-ray emitting boundary layer, and has
an excellent trigonometric parallax distance. We modeled the X-ray data using
XSPEC assuming a multi-temperature plasma emission model built from the MEKAL
code. We obtained a maximum temperature of 31.7 keV, based on the EPIC MOS1, 2
and pn data, indicating that RU Peg has an X-ray spectrum harder than most
dwarf novae, except U Gem. This result is consistent with and indirectly
confirms the large mass of the white dwarf in RU Peg. The X-ray luminosity we
computed corresponds to a boundary layer luminosity for a mass accretion rate
of 2.E-11 Msun/yr (assuming Mwd=1.3Msun), in agreement with an expected
quiescent accretion rate. The modeling of the O VIII emission line at 19A as
observed by the RGS implies a projected stellar rotational velocity of 695
km/s, i.e. the line is emitted from material rotating at about 936-1245 km/s
(for i about 34-48deg) or about 1/6 of the Keplerian speed; this velocity is
much larger than the rotation speed of the white dwarf inferred from the FUSE
spectrum. Cross-correlation analysis yielded an undelayed component and a
delayed component of 116 +/- 17 sec where the X-ray variations/fluctuations
lagged the UV variations. This indicates that the UV fluctuations in the inner
disk are propagated into the X-ray emitting region in about 116 sec. The
undelayed component may be related to irradiation effects.
