Optical, X-ray, and γ-ray observations of the candidate transitional millisecond pulsar 4FGL J0427.8-6704

We present an optical, X-ray, and gamma-ray study of 1SXPS J042749.2-670434, an eclipsing X-ray binary that has an associated gamma-ray counterpart, 4FGL J0427.8-6704. This association has led to the source being classified as a transitional millisecond pulsar (tMSP) in an accreting state. We analyse 10.5 yr of Fermi LAT data and detect a gamma-ray eclipse at the same phase as optical and X-ray eclipses at the >5 sigma level, a significant improvement on the 2.8 sigma level of the previous detection. The confirmation of this eclipse solidifies the association between the X-ray source and the gamma-ray source, strengthening the tMSP classification. However, analysis of several optical data sets and an X-ray observation do not reveal a change in the source's median brightness over long time-scales or a bi-modality on short time-scales. Instead, the light curve is dominated by flickering, which has a correlation time of 2.6 min alongside a potential quasi-periodic oscillation at similar to 21 min. The mass of the primary and secondary stars is constrained to be M-1 = 1.43(-0.19)(+0.33)M(circle dot) and M-2 = 0.3(-0.12)(+0.17)M(circle dot) through modelling of the optical light curve. While this is still consistent with a white dwarf primary, we favour the tMSP in a low accretion state classification due to the significance of the gamma-ray eclipse detection.