  Azimuthal correlations of charged particles in xenon-xenon collisions at a
center-of-mass energy per nucleon pair of $ \sqrt{s_{_\mathrm{NN}}} =$ 5.44 TeV
are studied. The data were collected by the CMS experiment at the LHC with a
total integrated luminosity of 3.42 $\mu$b$^{-1}$. The collective motion of the
system formed in the collision is parameterized by a Fourier expansion of the
azimuthal particle density distribution. The azimuthal anisotropy coefficients
$v_{2}$, $v_{3}$, and $v_{4}$ are obtained by the scalar-product, two-particle
correlation, and multiparticle correlation methods. Within a hydrodynamic
picture, these methods have different sensitivities to non-collective and
fluctuation effects. The dependence of the Fourier coefficients on the size of
the colliding system is explored by comparing the xenon-xenon results with
equivalent lead-lead data. Model calculations that include initial-state
fluctuation effects are also compared to the experimental results. The observed
angular correlations provide new constraints on the hydrodynamic description of
heavy ion collisions.
