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

Kennedy, M. R.; Breton, R. P.; Clark, C. J.; Dhillon, V. S.; Kerr, M.; Buckley, D. A. H.; Potter, S. B.; Mata Sánchez, D.; Stringer, J. G.; Marsh, T. R.
Bibliographical reference

Monthly Notices of the Royal Astronomical Society

Advertised on:
4
2020
Number of authors
10
IAC number of authors
1
Citations
17
Refereed citations
15
Description
We present an optical, X-ray, and γ-ray study of 1SXPS J042749.2-670434, an eclipsing X-ray 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 ∼21 min. The mass of the primary and secondary stars is constrained to be $M_1=1.43^{+0.33}_{-0.19}$ M☉ and $M_2=0.3^{+0.17}_{-0.12}$ 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.
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