~20 Jupiter mass object at ~1.5 AU from an X-ray binary?

Not sure what to make of this one.

Jain et al. "Indication of a massive circumbinary planet orbiting the Low Mass X-ray Binary MXB 1658-298"
https://arxiv.org/abs/1703.04433

I have several questions about how such a system could form, particularly taking into account the supernova that produced the neutron star in the system. Given the various problems with the planetary interpretation for cataclysmic variables, I'm wondering whether something similar to the Applegate mechanism might also be operating here.

Nice find, Lazarus. It's passed unnoticed.

Another study of the system (according to SIMBAD, it goes by both MXB 1658-298 and MXB 1659-298)

Iaria et al. "A possible solution of the puzzling variation of the orbital period of MXB 1659-298"
https://arxiv.org/abs/1703.05294

While they also consider the third-body hypothesis, they also note that the variations could be intrinsic to the companion star.

Quote :

Our results suggest that a change in the magnetic quadrupole of the companion star can produce the observed sinusoidal modulation. The required energy to transfer the angular momentum from the interior of the companion star to a thin shell, with a mass of 10% of M₂, at the surface (and viceversa) is furnished by ten percentage of the thermonuclear energy produced by the companion star.

The NASA Exoplanet Archive has added it as a planet.

https://exoplanetarchive.ipac.caltech.edu/cgi-bin/DisplayOverview/nph-DisplayOverview?objname=MXB+1658-298+b&type=CONFIRMED_PLANET