  During an XMM-Newton observation, the eclipsing polar UZ For was found in a
peculiar state with an extremely low X-ray luminosity and occasional X-ray and
UV flaring. For most of the observation, UZ For was only barely detected in
X-rays and about 800 times fainter than during a high state previously observed
with ROSAT. A transient event, which lasted about 900 s, was detected
simultaneously by the X-ray instruments and, in the UV, by the Optical Monitor.
The transient was likely caused by the impact of 10^17-10^18 g of gas on the
main accretion region of the white dwarf. The X-ray spectrum of the transient
is consistent with 7 keV thermal bremsstrahlung from the shock-heated gas in
the accretion column. A soft blackbody component due to reprocessing of X-rays
in the white dwarf atmosphere is not seen. The likely origin of the UV emission
during the transient is cyclotron radiation from the accretion column. We
conclude from our analysis that the unusual flaring during the low state of UZ
For was caused by intermittent increases of the mass transfer rate due to
stellar activity on the secondary.
