2025ApJ...991...91M

We present Chandra observations of 63 sources from the Gemini Near Infrared Spectrograph-Distant Quasar Survey, of which 54 were targeted by snapshot observations in Cycle 24. A total of 55 sources are clearly detected in at least one X-ray band, and we set stringent upper limits on the X-ray fluxes of the remaining eight sources. In combination with rest-frame ultraviolet-optical spectroscopic data for these sources, we assess whether X-rays can provide a robust accretion rate indicator for quasars, particularly at the highest accessible redshifts. We utilize a recently modified Hβ-based Eddington luminosity ratio estimator, as well as the C IVλ1549 emission-line parameter space, to investigate trends and correlations with the optical-X-ray spectral slope (α_ox) and the effective hard X-ray power-law photon index (Γ). We find that α_ox does not improve current accretion rate estimates based on Hβ or C IV. Instead, within the limitations of our sample, we confirm previous findings that the C IV parameter space may be a better indicator of the accretion rate up to z ∼ 3.5. We also find that the average Γ values for a small subset of our sources, as well as the average Γ value in different groupings of our sources, are consistent with their respective relatively high Eddington luminosity ratios. Deeper X-ray observations of our X-ray-detected sources are needed for measuring Γ accurately and testing whether this parameter can serve as a robust, unbiased accretion rate diagnostic.