VizieR Online Data Catalog: Optical, radio and X-ray properties for 113 QSOs (Huang+, 2020)

We investigate whether the correlation between the hard X-ray photon index (Γ) and accretion rate for super-Eddington accreting quasars is different from that for sub-Eddington accreting quasars. We construct a sample of 113 bright quasars from the Sloan Digital Sky Survey Data Release 14 quasar catalog, with 38 quasars as the super-Eddington subsample and 75 quasars as the sub-Eddington subsample. We derive black hole masses using a simple-epoch virial mass formula based on the Hβ lines, and we use the standard thin disk model to derive the dimensionless accretion rates (M) for our sample. The X-ray data for these quasars are collected from the Chandra and XMM-Newton archives. We fit the hard X-ray spectra using a single power-law model to obtain Γ values. We find a statistically significant (R_S=0.43, p=7.75x10^-3) correlation between Γ and M for the super-Eddington subsample. The Γ-M correlation for the sub-Eddington subsample is also significant, but weaker (R_S=0.30, p=9.98x10^-3). Linear regression analysis shows that Γ=(0.34{+/-}0.11)log(M)+(1.71{+/-}0.17) and Γ=(0.09{+/-}0.04)log(M)+(1.93{+/-}0.04) for the super- and sub-Eddington subsamples, respectively. The Γ-M correlations of the two subsamples are different, suggesting different disk-corona connections in these two types of systems. We propose one qualitative explanation of the steeper Γ-M correlation in the super-Eddington regime that involves larger seed photon fluxes received by the compact coronae from the thick disks in super-Eddington accreting quasars.

(2 data files).