  X-ray observations of the unique NLS1 galaxy Mrk 1239 spanning 18-years are
presented. Data from XMM-Newton, Suzaku, Swift and NuSTAR are combined to
obtain a broad-band, multi-epoch view of the source. There is spectral
variability in the 3-10 keV band over the 18-years. An analysis of the NuSTAR
and Suzaku light curves also suggests rapid variability in the 3-10 keV band,
which is consistent with the NLS1 definition of the source. However, no
variability is seen below 3 keV on any timescale. Two distinct physical models
are adopted to describe the data above and below ~3 keV. The low energies are
dominated by a hot, diffuse gas likely associated with a starburst component at
large physical scales. The higher energy spectrum is dominated by emission from
the central region. Ionised partial covering and relativistic blurred
reflection are considered for the central region emission. In both cases, the
underlying power law has a photon index of $\Gamma\sim2.3-2.4$. A distant
reflector, a neutral partial covering component with a covering fraction near
$\sim1$, and contributions from starburst emission are always required. The
blurred reflection model requires a reflection dominated spectrum, which may be
at odds with the low emissivity index and radio properties of the source. By
contrast, the two absorption components required in the ionised partial
covering model may correspond to the two distinct regions of polarization
observed in the optical. Regardless of the physical model, spectral changes
between epochs are driven by the absorption components and on short time scales
by intrinsic AGN variability.
