arXiv subjects

K. Khanthasombat

Publications and source records attributed to K. Khanthasombat.

2 recordsLinked to original sources

arXiv2025

Hybrid corona and transient soft X-ray lags in Fairall 9

Fairall 9 is among the most massive Seyfert galaxies exhibiting a strong soft X-ray excess, but it is challenging to probe soft X-ray reverberation lags (if any) due to the long intrinsic timescales expected from its large black hole mass of $\sim 2.55 \times 10^8 M_\odot$. We fit five XMM-Newton spectra of Fairall 9 using the hybrid reXcor model taking into account both hot and warm corona. The soft excess is explained by a combination of a physically motivated warm corona and the disc reflection. Then, we perform a wavelet coherence analysis of the light curves between 0.3 - 1 and 1 - 4 keV bands. The spectral fits are consistent with a rapidly spinning black hole ($a = 0.99$), a warm corona with optical depth $\sim$10 - 30, and a hot lamp-post corona located at either 5 or $20~r_{\rm g}$. This configuration supports a coexisting hot and warm corona scenario, allowing the disc to extend almost to the event horizon. Our wavelet analysis on combined observations reveals signatures of transient soft X-ray lags, confined to specific time-frequency intervals. The earlier observations exhibit more variable and transient lag behavior. In contrast, the later observations display more persistent soft X-ray lags at the frequencies of $\sim 9\times 10^{-6}$ - $2.5 \times 10^{-5}$ Hz, with amplitudes reaching $\sim$1000 s. The results indicate a progressively stable disc-corona configuration in later observations. Given the mass and geometry of Fairall 9, the observed soft lags appears plausibly consistent in both size and timescales with expectations from X-ray reverberation.

astro-ph.HE↗

arXiv2024

Parameter dependency on the public X-ray reverberation models kynxilrev and kynrefrev

We present a comparative study of the constrained parameters of active galactic nuclei (AGN) made by the public X-ray reverberation model kynxilrev and kynrefrev that make use of the reflection code xillver and reflionx, respectively. By varying the central mass ($M_{\rm BH}$), coronal height ($h$), inclination ($i$), photon index of the continuum emission ($Γ$) and source luminosity ($L$), the corresponding lag-frequency spectra can be produced. We select only the simulated AGN where their lag amplitude ($τ$) and $M_{\rm BH}$ follow the known mass-scaling law. In these mock samples, we show that $τ$ and $h$ are correlated and can possibly be used as an independent scaling law. Furthermore, $h$ (in gravitational units) is also found to be positively scaled with $M_{\rm BH}$, suggesting a more compact corona in lower-mass AGN. Both models reveal that the coronal height mostly varies between $\sim 5$-$15~r_{\rm g}$, with the average height at $\sim 10~r_{\rm g}$ and can potentially be found from low- to high-mass AGN. Nevertheless, the kynxilrev seems to suggest a lower $M_{\rm BH}$ and $h$ than the kynrefrev. This inconsistency is more prominent in lower-spin AGN. The significant correlation between the source height and luminosity is revealed only by kynrefrev, suggesting the $h$-$L$ relation is probably model dependent. Our findings emphasize the differences between these reverberation models that raises the question of biases in parameter estimates and inferred correlations.

astro-ph.HE↗