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Current estimates of the normalized accretion rates of quasars (L/L_Edd),rely on measuring the velocity widths of broad optical-UV emission lines (e.g.,H$\beta$ and Mg II $\lambda2800$). However, such lines tend to be weak orinaccessible in the most distant quasars, leading to increasing uncertainty inL/L_Edd estimates at $z > 6$. Utilizing a carefully selected sample of 53radio-quiet quasars that have H$\beta$ and C IV $\lambda1549$ spectroscopy aswell as {\sl Chandra} coverage, we searched for a robust accretion-rateindicator for quasars, particularly at the highest-accessible redshifts ($z\sim 6-7$). Our analysis explored relationships between the H$\beta$-basedL/L_Edd, the equivalent width (EW) of C IV, and the optical-to-X-ray spectralslope (a_ox). Our results show that EW(C IV) is the strongest indicator of theH$\beta$-based L/L_Edd parameter, consistent with previous studies, althoughsignificant scatter persists particularly for sources with weak C IV lines. Wedo not find evidence for the a_ox parameter improving this relation, and we donot find a significant correlation between a_ox and H$\beta$-based L/L_Edd.This absence of an improved relationship may reveal a limitation in our sample.X-ray observations of additional luminous sources, found at $z \gtrsim 1$, mayallow us to mitigate the biases inherent in our archival sample and testwhether X-ray data could improve L/L_Edd estimates. Furthermore, deeper X-rayobservations of our sources may provide accurate measurements of the hard-X-raypower-law photon index ($\Gamma$), which is considered an unbiased L/L_Eddindicator. Correlations between EW(C IV) and a_ox with $\Gamma$-based L/L_Eddmay yield a more robust prediction of a quasar normalized accretion rate.

Can X-ray Observations Improve Optical-UV-based Accretion-Rate Estimates for Quasars?