XMM/HST monitoring of the ultra-soft highly accreting narrow-line Seyfert 1 RBS 1332

Ultra-soft narrow-line Seyfert 1s (US-NLSy 1s) are a poorly observed class of active galactic nuclei characterised by significant flux changes and an extreme soft X-ray excess. This peculiar spectral shape represents a golden opportunity to test whether the standard framework commonly adopted for modelling local AGNs is still valid. We thus present the results of the joint XMM-Newton and HST monitoring campaign of the highly accreting US-NLSy RBS 1332. The optical-to-UV spectrum of RBS 1332 exhibits evidence for both a stratified narrow-line region and an ionised outflow that produces absorption troughs over a wide range of velocities (from ∼–1500 km s−1 to ∼1700 km s−1) in several high-ionisation transitions (Lyα, N <ns0:sc>V</ns0:sc>, C <ns0:sc>IV</ns0:sc>). From a spectroscopic point of view, the optical/UV/FUV/X-ray emission of this source is due to the superposition of three distinct components that are best modelled in the context of the two-coronae framework in which the radiation of RBS 1332 can be ascribed to a standard outer disc, a warm Comptonisation region, and a soft coronal continuum. The present dataset is not compatible with a pure relativistic reflection scenario. Finally, the adoption of the novel model <ns0:sc>RE</ns0:sc>X<ns0:sc>COR</ns0:sc> allowed us to determine that the soft X-ray excess in RBS 1332 is dominated by the emission of the optically thick and warm Comptonising medium, and only a marginal contribution is expected from relativistic reflection from a lamppost-like corona.