A Multi-Wavelength Study of the Gamma-Ray Binary 1FGL J1018.6-5856

1FGL J1018.6-5856, the first gamma-ray binary discovered by the Fermi Large Area Telescope (LAT), consists of an O6 V((f)) star and suspected rapidly spinning pulsar. While 1FGL J1018.6-5856 has been postulated to be powered by the interaction between a relativistic pulsar wind and the stellar wind of the companion, a microquasar scenario where the compact object is a black hole cannot be ruled out. We present the first extensive multi-wavelength analysis of 1FGL J1018.6-5856 with the Australia Telescope Compact Array (ATCA), Fermi LAT and the Swift X-ray Telescope (XRT) to better determine the properties of the 16.531$\pm$0.006 day orbital modulation. The radio amplitude modulation is found to decline with increasing frequency, which is a possible indication of the presence of free-free absorption. This is further supported by the absence of clear modulation in the 33.0 and 35.0\,GHz bands, which were not previously reported. The best-fit spectral model of the Swift XRT data consists of a featureless power law with index $\Gamma\sim$1.3--1.7 modified by an absorber that fully covers the source. This is possible evidence that 1FGL J1018.6-5856 is a non-accreting system.