Constraining Disk-to-Corona Power Transfer Fraction, Soft X-ray Excess Origin, and Black Hole Spin Population of Type-1 AGN across Mass Scales

TL;DR

This study uses broadband X-ray spectra to analyze accretion disk and corona interactions, measure black hole spins, and explore the soft X-ray excess in Type-1 AGN, revealing diverse disk-to-corona power transfer fractions and expanding spin data.

Contribution

It provides the first calculation of the disk-to-corona power transfer fraction and systematically constrains black hole spins across a broad mass range in AGN.

Findings

High-density relativistic reflection model fits 70% of spectra

Median disk-to-corona power transfer fraction is 0.7

Black hole spins constrained across masses 10^5.5 to 10^9 solar masses

Abstract

Understanding the nature of the accretion disk, its interplay with the X-ray corona, and assessing black hole spin demographics are some open challenges in astrophysics. In this work, we examine the predictions of the standard $\alpha$-disk model, origin of the soft X-ray excess, and measure the black hole spin parameter by applying the updated high-density disk reflection model to the XMM-Newton/NuSTAR broadband (0.3$-$78 keV) X-ray spectra of a sample of Type-1 AGN. Our Bayesian analysis confirms that the high-density relativistic reflection model with a broken power-law emissivity profile can simultaneously fit the soft X-ray excess, broad iron K line, and Compton hump for $\sim$70% of the sample, while an additional warm Comptonization model is still required to describe the observed soft X-ray excess for the remaining sources. Our first-ever calculation of the disk-to-corona power transfer fraction reveals that the fraction of power released from the accretion disk into the hot corona can have diverse values, the sample median of which is $0.7_{-0.4}^{+0.2}$. We find that the transferred power from the accretion disk can potentially soften the X-ray spectrum of the hot corona. The median values of the hot coronal temperature and optical depth for the sample are estimated to be $63_{-11}^{+23}$ keV and $0.85_{-0.27}^{+0.12}$, respectively. Finally, through joint XMM-Newton+NuSTAR relativistic reflection spectroscopy, we systematically constrain the black hole spin parameter across the broad range of black hole masses, $\log(M_{\rm BH}/M_{\odot}) \sim 5.5-9.0$, and increase the available spin measurements in the AGN population by $\sim$20%.