arXiv subjects

Kristína Kallová

Publications and source records attributed to Kristína Kallová.

3 recordsLinked to original sources

arXiv2026

Extreme Variability Reveals How the Eddington Ratio Regulates Coronal Power in Active Galactic Nuclei

The bolometric luminosity ($L_{\rm bol}$) of active galactic nuclei (AGNs) is a key tracer of accretion physics, but its direct determination is often hindered by limited spectral coverage and contamination of the host galaxy. Bolometric corrections ($κ_λ = L_{\rm bol}/L_λ$) offer a practical means of estimating $L_{\rm bol}$, with the X-ray bolometric correction ($κ_{\rm 2-10}$) being crucial for exploring the coupling between the accretion disk and the X-ray corona. Here we present multi-epoch, multi-wavelength observations of five highly variable, changing-state AGNs that span more than three orders of magnitude in Eddington ratio ($-3.6\lesssim \log λ_{\rm Edd} \lesssim -0.5$). This unique data set reveals a remarkably tight relation between $κ_{\rm 2-10}$ and $λ_{\rm Edd}$, with an intrinsic scatter of only $\sim0.05$ dex. We find that while the sources show bolometric corrections following different tracks in luminosity space that depend on black hole mass, they all display the same $κ_{\rm 2-10}-λ_{\rm Edd}$ trend. This shows unambiguously that $λ_{\rm Edd}$ is the primary driver of X-ray bolometric corrections, and points to a tight underlying trend that can be used to obtain reliable estimates of bolometric output from X-ray luminosities. Our results highlight how time-domain, multi-wavelength observations of variable AGN offer unique insights into the accretion flow structure and its radiative output.

astro-ph.GA↗

arXiv2026

Multi-wavelength properties of changing-state active galactic nuclei: I. the evolution of soft excess and X-ray continuum

Changing-state active galactic nuclei (CSAGNs) exhibit rapid variability, with mass accretion rates that can change by several orders of magnitude in a few years. This provides us with a unique opportunity to study the evolution of the inner accretion flow almost in real time. Here, we used over 1000 observations to study the broadband X-ray spectra of a sample of five CSAGNs, spanning three orders of magnitude in Eddington ratio ($λ_{\rm Edd}$), using phenomenological models to trace the evolution of key spectral components. We derive several fundamental parameters, such as the photon index, soft excess strength, reflection strength, and luminosities of the soft excess and primary continuum. We find that the soft excess and primary continuum emissions show a very strong positive correlation ($p \ll 10^{-10}$), suggesting a common physical origin. The soft excess strength does not show any dependency on the reflection parameter, suggesting that in these objects the soft excess is not dominated by a blurred ionized reflection process. On the other hand, the strength of the soft excess is found to be strongly positively correlated with the Eddington ratio ($p \ll 10^{-10}$), and we find that the soft excess vanishes below $\log λ_{\rm Edd} \sim -2.5$. Moreover, we find a clear `V'-shaped relation for $Γ-λ_{\rm Edd}$, with a break at $\log λ_{\rm Edd} = -2.47 \pm 0.09$. Our findings indicate a change in the geometry of the inner accretion flow at low Eddington ratios, and that the soft excess is primarily produced via warm Comptonization.

astro-ph.HE↗

arXiv2024

Investigating model dependencies for obscured Active Galactic Nuclei: a case study of NGC 3982

X-ray spectroscopy of heavily obscured Active Galactic Nuclei (AGN) offers a unique opportunity to study the circum-nuclear environment of accreting supermassive black holes (SMBHs). However, individual models describing the obscurer have unique parameter spaces that give distinct parameter posterior distributions when fit to the same data. To assess the impact of model-specific parameter dependencies, we present a case study of the nearby heavily obscured low-luminosity AGN NGC 3982, which has a variety of column density estimations reported in the literature. We fit the same broadband XMM-Newton + NuSTAR spectra of the source with five unique obscuration models and generate posterior parameter distributions for each. By using global parameter exploration, we traverse the full prior-defined parameter space to accurately reproduce complex posterior shapes and inter-parameter degeneracies. The unique model posteriors for the line-of-sight column density are broadly consistent, predicting Compton-thick $N_{\rm H}$ $>1.5\times10^{24}\rm cm^{-2}$ at the 3$σ$ confidence level. The posterior median intrinsic X-ray luminosity in the 2-10 keV band however was found to differ substantially, with values in the range log $L_{ 2-10\,{\rm keV}}$ergs$^{-1}$ = 40.9-42.1 for the individual models. We additionally show that the posterior distributions for each model occupy unique regions of their respective multi-dimensional parameters spaces, and how such differences can propagate into the inferred properties of the central engine. We conclude by showcasing the improvement in parameter inference attainable with the High Energy X-ray Probe (HEX-P) with a uniquely broad simultaneous and high-sensitivity bandpass of 0.2-80 keV.

astro-ph.HE↗