2024MNRAS.528.1542M

X-ray properties of active galactic nuclei (AGNs) depend on their underlying physical parameters, particularly the accretion rate. We identified eight reverberation-mapped AGNs with some of the largest known accretion rates without high-quality X-ray data. We obtained new Chandra ACIS-S X-ray observations and nearly simultaneous optical spectrophotometry to investigate the properties of these AGNs with extreme super-Eddington accreting massive black holes (SEAMBHs). We combined our new X-ray measurements with those of other reverberation-mapped AGNs, which have the best-determined masses and accretion rates. The trend of the steepening of the spectral slope between X-ray and optical-UV, α_ox, with increasing optical-UV luminosity, $L_{\rm 2500{\mathring{\rm A}}}$, holds true for even the most extreme SEAMBHs. One of our new SEAMBHs appears X-ray-weak for its luminosity, perhaps due to absorption associated with orientation effects involving a slim disc thought to be present in highly accreting systems. The correlation of the $\rm 2\!-\!8~ keV$ X-ray photon index with the accretion rate also holds for the extreme SEAMBHs, which show some of the largest photon indices reported for AGNs.