The total mass of the Large Magellanic Cloud from its perturbation on
  the Orphan stream
  In a companion paper by Koposov et al., RR Lyrae from \textit{Gaia} Data
Release 2 are used to demonstrate that stars in the Orphan stream have velocity
vectors significantly misaligned with the stream track, suggesting that it has
received a large gravitational perturbation from a satellite of the Milky Way.
We argue that such a mismatch cannot arise due to any realistic static Milky
Way potential and then explore the perturbative effects of the Large Magellanic
Cloud (LMC). We find that the LMC can produce precisely the observed
motion-track mismatch and we therefore use the Orphan stream to measure the
mass of the Cloud. We simultaneously fit the Milky Way and LMC potentials and
infer that a total LMC mass of $1.38^{+0.27}_{-0.24}
\times10^{11}\,\rm{M_\odot}$ is required to bend the Orphan Stream, showing for
the first time that the LMC has a large and measurable effect on structures
orbiting the Milky Way. This has far-reaching consequences for any technique
which assumes that tracers are orbiting a static Milky Way. Furthermore, we
measure the Milky Way mass within 50 kpc to be
$3.80^{+0.14}_{-0.11}\times10^{11} M_\odot$. Finally, we use these results to
predict that, due to the reflex motion of the Milky Way in response to the LMC,
the outskirts of the Milky Way's stellar halo should exhibit a bulk, upwards
motion.
