X-ray view of dissipative warm corona in active galactic nuclei

TL;DR

This study investigates the dissipative warm corona in active galactic nuclei using spectral modeling of X-ray data, revealing its widespread presence, properties, and correlation with accretion parameters, thus advancing understanding of AGN coronae.

Contribution

The paper applies radiative transfer modeling to a large sample of AGN X-ray spectra, providing new estimates of warm corona properties and their relation to accretion physics.

Findings

Warm corona optical depths range from 6 to 30.

Total internal heating varies between 1-29 x 10^-23 erg/s-cm^3.

Warm corona extent spans 7-408 gravitational radii.

Abstract

In the X-ray spectra of AGNs, a noticeable excess of soft X-rays is typically detected beyond the extrapolation of the power-law trend observed between 2-10 keV. In the scenario of warm Comptonization, observations propose a warm corona temperature ranging from 0.1-1 keV and an optical depth of approximately 10-20. Furthermore, according to radiative constraints derived from spectral analyses employing Comptonization models, it is suggested that the majority of the accretion power is released within the warm corona, while the disk beneath it is largely non-dissipative, emitting mainly the reprocessed radiation from the corona. We test the dissipative warm corona model using the radiative transfer code-TITAN/NOAR on a sample of 82 XMM-Newton observations of AGNs. Through spectral modeling of the X-ray data, we aim to estimate the total amount of internal heating inside the warm corona situated on top of the accretion disk. By modeling the 0.3-10 keV EPIC-pn spectra, we estimate the internal heating and optical depth of the warm corona and check their correlations with global parameters blackhole parameters. From model normalization, we compute the radial extent of warm corona on top of cold accretion disk. Our model infers the presence of dissipative warm corona, with optical depths distributed in the range 6-30 and total internal heating in the range 1-29 x 1e-23 erg/s-cm3. The extent of warm corona is spread across a large range from 7-408 gravitational radii, and we find that warm corona is more extended for larger accretion rates. Soft excess emission is ubiquitous in AGNs across wide mass range and accretion rate. We confirm that warm corona responsible for producing the soft-excess is highly dissipative in nature with larger optical depths being associated with lower internal heating and vice versa. The cold standard accretion disk regulates the extent of warm corona.