2025ApJ...991..103S

Using the Cosmic Origins Spectrograph (COS) on board the Hubble Space Telescope with both far-UV (FUV) and near-UV (NUV) gratings, we measure the ionizing spectra of two bright, intermediate-redshift quasars in their rest-frame extreme ultraviolet (EUV). The availability of both NUV and FUV spectra allows us to define the quasar continuum and correct for strong Lyman-limit systems (LLSs) that fall in the gap between the FUV and optical. Each active galactic nucleus (AGN) has a prominent LLS, but the flux recovery shortward of their Lyman edges allows us to fit and restore the true AGN continuum. In the EUV (450-912 Å), these AGN have flux distributions, ${F}_{\nu }\propto {\nu }^{-{\alpha }_{\nu }}$, with spectral indices α_ν = 1.11 ± 0.22 (SBS 1010+535, z_AGN = 1.5086) and α_ν = 0.98 ± 0.22 (HS 0747+4259, z_AGN = 1.9006), both considerably harder than the mean index, α_ν = 1.41 ± 0.15, in a COS composite spectrum of 159 UV-bright AGN. These two AGN are outliers in the index distribution, perhaps resulting from their extremely high UV luminosity (0.4-0.9) × 10⁴⁸ erg s^–1), estimated black-hole masses (0.5-1) × 10¹⁰M_⊙, and effects on the inner accretion disk and Comptonized winds.