Supermassive Black Hole Winds in X-rays: SUBWAYS. V. Properties of hot coronae in quasars at intermediate-redshift

We present the X-ray analysis of coronal properties in a statistically representative sample of 23 mostly radio-quiet active galactic nuclei (AGN) from the SUpermassive Black holes Winds in X-rAYs campaign (SUBWAYS), focusing on quasars at redshifts 0.1<z<0.4 and bolometric luminosities 2 <L_ 44 bol ( erg/s)<2 . The main aim of this work is to investigate the properties of the hot corona through the study of the hard X-ray band emission, including a proper treatment of the soft X-ray band. High-quality X-ray spectra from 46 complemented by νstar data extending up to 30–40 keV in the rest frame, are available for this sample. The soft X-ray band (0.3–2 keV) spectrum is best fit by a warm corona model with a median temperature of sim0.40 keV, and an optical depth in the range τ consistent with previous results on lower-luminosity sources. The hard X-ray band is well described using a hot corona model, with a median high-energy cutoff of sim87 keV; 11 out of 23 of the sources have well constrained values at the lower end of the distribution of typical values found in Seyfert galaxies (sim100-200 keV). The derived median value of the optical depth (τ∼ 1-5) suggests the presence of a moderately optically thick corona. By combining the SUBWAYS results with literature samples at low and high redshifts, we assembled the largest sample to date of AGN with E_cut and accretion parameter measurements, finding a significant anticorrelation of E_cut with both λ_̊m Edd and łbol, with the median E_cut decreasing from sim250-300 keV at low accretion rates and luminosities to sim90-100 keV at high accretion rates and luminosities; this is consistent with increased coronal cooling, possibly driven by pair production. These results favor cooler, optically thicker coronae in luminous AGN compared to those in lower-luminosity Seyfert galaxies.