  The gamma-ray binary 1FGL J1018.6-5856 consists of an O6V((f)) type star and
an unknown compact object, and shows orbitally modulated emission from radio to
very high energy gamma rays. The X-ray light curve shows a maximum around the
same phase as the GeV emission, but also a secondary maximum between phases
$\phi=0.2 - 0.6$. A clear solution to the binary system is important for
understanding the emission mechanisms occurring within the system. In order to
improve on the existing binary solution, we undertook radial velocity
measurements of the optical companion using the Southern African Large
Telescope, as well as analysed publicly available X-ray and GeV gamma-ray data.
A search for periodicity in Fermi-LAT data found an orbital period of
$P=16.5507\pm0.0004$ d. The best fit solution to the radial velocities, held at
this new period, finds the system to be more eccentric than previous
observations, $e=0.531 \pm 0.033$ with a longitude of periastron of $151.2 \pm
5.1^\circ$, and a larger mass function $f = 0.00432\pm 0.00077$ M$_\odot$. We
propose that the peaks in the X-ray and gamma-ray light curves around phase 0
are due to the observation of the confined shock formed between the pulsar and
stellar wind pointing towards the observer. The secondary increase or strong
rapid variations of the X-ray flux at phases 0.25-0.75 is due to the
interaction of multiple randomly oriented stellar wind clumps/pulsar wind
interactions around apastron.
