  Abridged. The LINER galaxy TXS2226-184 is known to host a very luminous 22
GHz water maser, called a gigamaser at the time of its discovery. To date, the
nature of this maser is still being debated, in particular, whether it is
associated with a nuclear accretion disk or with an ejection component, namely
a jet or an outflow originating in the active galactic nucleus. We obtained
multi-band (bands 5, 6, and 7) ALMA observations during Cycle 9, with the
purpose of investigating the maser nature and the nuclear molecular material in
the innermost region of the galaxy. While the full data sets are still under
study, a preliminary data reduction and analysis of the band 5 and 7 spectral
line cubes presented in this Letter already offer a significant outcome. We
observed bright, possibly maser emission from the water 183 GHz and 380 GHz
transitions in TXS2226. To the best of our knowledge, this represents the first
unambiguous detection (S/N >= 100) of 380 GHz maser emission in a known 22-GHz
maser galaxy, and the first case where all three transitions are present in the
same object. Emission features at both frequencies show a two-peaked line
profile resembling that of the 22 GHz maser features. The mm/submm emission
originates from a region coincident, within the errors, with that of the 22
GHz. The similarities in profile and position indicate that the emission at the
three frequencies is likely produced by the same nuclear structure, although
differences in line strengths and feature peak positions may hint at a slightly
different physical conditions of the emitting gas. A comparison with the few
megamaser sources studied at high enough detail and sharing similarities with
the water lines in TXS2226 favors a nature associated with the amplification of
a bright nuclear continuum (from a jet or outflow) through dense and hot gas in
front of the nucleus (e.g., a disk or torus)...
