2023MNRAS.518.6065J

RX J0134.2-4258 is one of the most super-Eddington narrow-line Seyfert 1 (NLS1) galaxies, on which we conducted a monitoring campaign from radio to X-rays. In this paper, we present a detailed analysis of its optical/UV spectra and broad-band spectral energy distribution. Our study shows that the preferred black hole mass of RX J0134.2-4258 is M_BH ∼ 2 × 10⁷ M_⊙, giving a mass accretion rate through the outer disc of $\dot{m}_{\rm out} \sim 20$ (assuming zero spin), compared to the observed luminosity ratio L_bol/L_Edd ∼ 6. This reduction in radiative efficiency is expected for super-Eddington flows, as power can be lost via advection and/or disc winds. We find that the optical/UV lines of RX J0134.2-4258 resemble those from weak-like quasars (WLQs), as it has notably weak C IV and N V emission lines. It also has drastic X-ray variability, again similar to that recently observed in some other WLQs. However, WLQs have systematically higher masses (≳10⁸ M_⊙), and lower Eddington ratios ($\dot{m}_{\rm out} \sim 1$) than RX J0134.2-4258. We compare instead to the most extreme NLS1s, with similarly large $\dot{m}_{\rm out}$ but smaller masses. These show similarly large reductions in radiative efficiency but their UV lines are not similarly wind dominated. We suggest a new category of weak-line Seyfert galaxies to describe sources like RX J0134.2-4258, and interpret its (so far unique) properties in a model, where the lower disc temperature in the higher mass black holes leads to the UV-line-driving mechanism, which enhances the super-Eddington radiation-pressure-driven wind.