Confirm the predicted far-UV polarized-flux bump in Mrk 231

Determine whether the predicted second bump in the far-ultraviolet polarized flux of Mrk 231 is genuinely present, and thereby assess the validity of the binary supermassive black hole interpretation of the quasar.

Background

The analytical binary-supermassive-black-hole model predicts a second bump in Mrk 231’s far-ultraviolet polarized flux, attributed to emission from the less massive secondary black hole. This feature could provide an observational signature distinguishing the binary configuration from alternative explanations of the quasar’s unusual ultraviolet spectropolarimetric properties.

The available far-ultraviolet observations are too sparsely sampled to establish whether the predicted feature exists. Higher-sensitivity far-ultraviolet spectropolarimetric observations are therefore required both to confirm or reject the bump and to evaluate whether the binary-supermassive-black-hole scenario can account for Mrk 231’s observations.

References

However, the current far-UV data remain poorly sampled, which prevents us from confirming the presence of the predicted bump with high confidence.

— Probing binary supermassive black hole in quasars tough spectropolarimetry  (2609.29441 - Biedermann et al., 24 Sep 2026) in Section 2.2, “Polarimetric modeling”