We present an optical, X-ray, and $gamma$-ray study of 1SXPS J042749.2-670434, an eclipsing X-ray binary which 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 years 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 sources median brightness over long timescales or a bi-modality on short timescales. 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 star are constrained to be $M_1=1.43^{+0.33}_{-0.19}$ M$_{odot}$ and $M_2=0.3^{+0.17}_{-0.12}$ M$_{odot}$ through modelling of the optical light curve. While this is still consistent with a white dwarf primary, we favour the transitional millisecond pulsar in a low accretion state classification due to the significance of the $gamma$-ray eclipse detection.
Download