  We present the results of an investigation of the X-ray and UV properties of
four LINERs observed with Swift, aimed at constructing good S/N and strictly
simultaneous UV-X-ray SEDs. In the current paradigm, LINER emission is
dominated by geometrically thick, radiatively inefficient radiation flows
(RIAFs) as opposed to radiatively efficient, geometrically thin accretion disks
thought to power higher luminosity AGNs (Seyferts and QSOs). However, some
recent studies have found more similarities than differences between the SEDs
of LINERs and those of more luminous AGNs, suggesting that LINERs are powered
by the same mechanisms active in higher luminosity AGNs. Our new observations
allow us to test this idea. In particular, XRT affords long and sensitive
monitoring of the X-ray emission. We detect significant variability in M81 and,
for the first time, in NGC 3998. The maximum amplitude variations over time
scales of some hours are 30% in both M81 and NGC 3998. NGC 3998 exhibits a
variation of the same amplitude on a time scale of 9 days. M81 varies
significantly over 2 years, with a maximum change of a factor 2 in 6 months.
The X-ray variability detected in 2 of our sources, and in particular in NGC
3998, puts into question the interpretation of their powering mechanism as an
inefficient accretion flow, because one of the characteristics of this model is
the lack of variability. The identification of NGC 3998 with a low power AGN
appears more viable.
