XMM-Newton Ultra Narrow Deep Field survey II: X-ray spectral analysis of the brightest AGN population

In this work, we present the results of a detailed X-ray spectral analysis of the brightest AGNs detected in the XMM-Newton 1.75 Ms Ultra Narrow Deep Field. We analyzed 23 AGNs that have a luminosity range of ~ 10⁴² - 10⁴⁶\, erg\, s⁻¹ in the 2 - 10\, keV energy band, redshifts up to 2.66, and ~ 10,000 X-ray photon counts in the 0.3 - 10\, keV energy band. Our analysis confirms the Iwasawa-Taniguchi effect, an anti-correlation between the X-ray luminosity (Lₓ) and the Fe-kα Equivalent Width (EWFe) possibly associated with the decreasing of the torus covering factor as the AGN luminosity increases. We investigated the relationship among black hole mass (MBH), Lₓ, and X-ray variability, quantified by the Normalized Excess Variance (σ²ᵣₘₛ). Our analysis suggest an anti-correlation in both MBH - σ²ᵣₘₛ and Lₓ- σ²ᵣₘₛ relations. The first is described as σ²ᵣₘₛ ∝ M-0.26 ± 0.05BH, while the second presents a similar trend with σ²ᵣₘₛ ∝ Lₓ-0.31 ± 0.04. These results support the idea that the luminosity-variability anti-correlation is a byproduct of an intrinsic relationship between the BH mass and the X-ray variability, through the size of the emitting region. Finally, we found a strong correlation among the Eddington ratio (λEdd), the hard X-ray photon index (Γ), and the illumination factor log(A), which is related to the ratio between the number of Compton scattered photons and the number of seed photons. The log(λEdd)-Γ-log(A) plane could arise naturally from the connection between the accretion flow and the hot corona.