  IGR J14091-6108 is a Galactic X-ray source known to have an iron emission
line, a hard X-ray spectrum, and an optical counterpart. Here, we report on
X-ray observations of the source with XMM-Newton and NuSTAR as well as optical
spectroscopy with ESO/VLT and NOAO/SOAR. In the X-rays, this provides data with
much better statistical quality than the previous observations, and this is the
first report of the optical spectrum. Timing analysis of the XMM data shows a
very significant detection of 576.3+/-0.6 s period. The signal has a pulsed
fraction of 30%+/-3% in the 0.3-12 keV range and shows a strong drop with
energy. The optical spectra show strong emission lines with significant
variability in the lines and continuum, indicating that they come from an
irradiated accretion disk. Based on these measurements, we identify the source
as a magnetic Cataclysmic Variable of Intermediate Polar (IP) type where the
white dwarf spin period is 576.3 s. The X-ray spectrum is consistent with the
continuum emission mechanism being due to thermal Bremsstrahlung, but partial
covering absorption and reflection are also required. In addition, we use the
IP mass (IPM) model, which suggests that the white dwarf in this system has a
high mass, possibly approaching the Chandrasekhar limit.
