  We present a detailed X-ray spectral and variability study of the full 2018
outburst of MAXI J1727-203 using NICER observations. The outburst lasted
approximately four months. Spectral modelling in the 0.3-10 keV band shows the
presence of both a soft thermal and a hard Comptonised component. The analysis
of these components shows that MAXI J1727-203 evolved through the soft,
intermediate and hard spectral states during the outburst. We find that the
soft (disc) component was detected throughout almost the entire outburst, with
temperatures ranging from ~0.4 keV, at the moment of maximum luminosity, to
~0.1 keV near the end of the outburst. The power spectrum in the hard and
intermediate states shows broadband noise up to 20 Hz, with no evidence of
quasi-periodic oscillations. We also study the rms spectra of the broadband
noise at 0.3-10 keV of this source. We find that the fractional rms increases
with energy in most of the outburst except during the hard state, where the
fractional rms remains approximately constant with energy. We also find that,
below 3 keV, the fractional rms follows the same trend generally observed at
energies >3 keV, a behaviour known from previous studies of black holes and
neutron stars. The spectral and timing evolution of MAXI J1727-203, as
parametrised by the hardness-intensity, hardness-rms, and rms-intensity
diagrams, suggest that the system hosts a black hole, although we could not
rule out a neutron star.
