XMM and NuSTAR Observations of an Optically Quiescent Quasar

Abstract

Optically quiescent quasars (OQQs) represent a recently systematized class of infrared-luminous active galactic nuclei (AGNs) that have galaxy-like optical continua. They may represent an interesting, brief phase in the AGN life cycle, e.g., either cocooned within high-covering-factor media or indicative of recent triggering, though their nature remains unclear. Here, we present the first targeted simultaneous X-ray observations of an OQQ, our previously identified prototype, SDSS J075139.06+402811.2 at z = 0.587. The source is significantly detected over 0.5-16 keV with XMM-Newton and NuSTAR, unambiguously confirming the presence of current accretion activity. Spectral modeling yields an intrinsic luminosity L _{2-10 keV} ≈ 4.4 × 10⁴³ erg s^-1, well within the AGN regime, but underluminous relative to its infrared power. It is lightly obscured, with log N _H [cm^-2] ≈ 22.