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

We present an optical, X-ray, and γ -ray study of 1SXPS J042749.2-670434, an eclipsing Xray binary that has an associated γ -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 γ -ray eclipse at the same phase as optical and X-ray eclipses at the >5 σ level, a significant improvement on the 2.8 σ level of the previous detection. The confirmation of this eclipse solidifies the association between the X-ray source and the γ -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 sim;21 min. The mass of the primary and secondary stars is constrained to beM1 = 1.43+0.33 -0.19 M⊙ andM2 = 0.3+0.17 -0.12 M⊙ 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 γ -ray eclipse detection.