arXiv subjects

Poemwai Chainakun

Publications and source records attributed to Poemwai Chainakun.

9 recordsLinked to original sources

arXiv2026

Radial Velocity Evidence for a Post-Mass-Transfer Massive Binary System NaSt1

We present multi-epoch high-resolution optical spectroscopy ($R \simeq 80{,}000$) of the emission-line object NaSt1 to test its proposed binary nature, along with long-term multiband photometry, mid-infrared spectroscopy, and spatially resolved integral field unit (IFU) spectroscopy to probe the circumstellar kinematics of the system. We detect two groups of 36 emission lines showing radial velocity (RV) variation with a mean period of 311 $\pm$ 5 d, but varying in opposite phase. We associate these two groups with the optically thick wind of the stripped primary star and the wind-wind collision region with the companion star, providing strong evidence for binarity. The RV and light curve (LC) periods are consistent within the uncertainties, ruling out ellipsoidal modulation, which would require an orbital period of about 620 d. The RV-LC phase relationship and high-ionization lines favor binary interaction over pulsations. We model the 1--5~$\mu$m spectrum of NaSt1 and find two optically thin dust components: hot $T_{\rm h} \simeq 1230$ K, $M_{\rm h} \simeq 2 \times 10^{-10} M_{\odot}$ and warm $T_{\rm c} \simeq 660$ K, $M_{\rm c} \simeq 3 \times 10^{-8} M_{\odot}$. IFU spectroscopy spatially resolves the circumstellar medium in the [\ion{N}{2}] $\lambda6548$ and $\lambda6584$ emission lines, showing a deprojected expansion velocity of $\sim31$ km~s$^{-1}$, implying a dynamical age of $\sim40$ yr. This short timescale suggests that the nebula was produced by recent mass loss. The system may represent a Galactic analog of a massive binary undergoing a mass-loss process to become a stripped-envelope supernova progenitor.

astro-ph.SR↗

arXiv2026

Extraction method for response functions from X-ray light curves of AGN by optimization algorithm

We introduce a numerical optimization method to extract the X-ray reverberation response functions from the multi-band light curves of the active galactic nuclei. This approach does not require prior assumptions about the accretion disc and corona geometry, provided that the light curves result from the superposition of direct and singly-convolved signals, consistently across all bands. By reformulating the light curve equations into the matrix form, the optimal response matrix is derived by minimizing the squared difference between the observed and reconstructed light curves using a gradient-based optimization algorithm. We demonstrate that the method can robustly accommodate up to two convolution processes, such as the reverberation and the propagation, simultaneously. When tested on the synthesized light curves, the method demonstrates robustness of the solutions to variations in the relative contributions of each light curve component as the recovered response kernel remains acceptably close to the ground truth, as evaluated by both the response geometry and the reconstructed light curves. The method's tolerance to random noise was also assessed. With appropriate denoising, the response kernel can be reliably recovered when the signal-to-noise ratio is at least $100$. We show, as a proof of concept, that the proposed method is geometrical-model independent and has the potential to offer a flexible complement to traditional approaches.

astro-ph.HE↗

arXiv2026

An infrared echo from a circumstellar disk in the hydrogen- and helium-poor SN 2024aecx

We present near-infrared (NIR) spectroscopy of the hydrogen- and helium-poor (Type Ic) supernova (SN) 2024aecx, which displays a strong NIR excess emerging 32 days post peak. SN 2024aecx is a peculiar SN Ic that exhibited luminous shock-cooling emission at early times, suggestive of close-in circumstellar medium (CSM), unexpected for this class of SNe. Its early NIR spectra are typical for a SN Ic but with strong C I absorption features. By $\sim$32 days post peak, the spectra show a strong NIR excess, while maintaining normal optical colors, unprecedented for SNe Ic. We find that the NIR excess is well fit with a single-temperature, optically thin dust model with declining temperature, increasing mass, and roughly constant luminosity over time. The NIR excess appears too promptly for dust to have formed in the SN ejecta, indicating an IR echo from pre-existing dust in the CSM. The IR echo is likely powered by the relatively slowly evolving SN peak light, and not the brief shock cooling emission, as the latter requires unrealistically high CSM densities to explain the observed dust mass. We consider different potential CSM geometries and find that a thick face-on disk with an inner edge of around $5\times 10^{16} \rm \ cm$ can best explain the dust mass and temperature evolution. In this scenario, the SN shock should start interacting with this CSM $440\pm200$ days post explosion. CSM around SN Ic is rare, and follow-up observations of SN 2024aecx will probe the mass-loss process responsible for removing hydrogen and helium from their progenitor star.

astro-ph.HE↗

arXiv2025

The brightest X-ray AGNs at redshift $3\lesssim z \lesssim 6$

Given recent X-ray observations of high-redshift active galactic nuclei (AGNs), we consider whether the extreme luminosities of these AGNs are consistent with current semi-analytical models. In particular, we apply extreme-value statistics (EVS) to obtain predictions of extreme X-ray luminosities of AGNs in the redshift range $3\lesssim z\lesssim 6$. We apply this formalism using different X-ray luminosity functions and compare the predicted extreme luminosities to AGNs in the Stripe 82 X-ray catalogue. We find a general consistency between data and the EVS predictions although there is some tension with certain luminosity functions. We discuss possible extensions to this model, including extrapolating our results to even higher redshifts ($z\gtrsim10$) where AGNs have recently been observed.

astro-ph.GA↗

arXiv2025

Extracting the X-ray reverberation response functions from the AGN light curves using an autoencoder

We study the X-ray reverberation in active galactic nuclei (AGN) using the variational autoencoder (VAE), which is a machine-learning algorithm widely used for signal processing and feature reconstruction. While the X-ray reverberation signatures that contain the information of the accretion disk and the X-ray emitting corona are commonly analyzed in the Fourier domain, this work aims to extract the reverberation response functions directly from the AGN light curves. The VAE is trained using the simulated light curves that contain the primary X-rays from the lamp-post corona varying its height and the corresponding reflection X-rays from the disk. We use progressively more realistic light-curve models, such as those that include the effects of disk-propagating fluctuations and random noises, to assess the ability of the VAE to reconstruct the response profiles. Interestingly, the VAE can recognize the reverberation patterns on the light curves, hence the coronal height can be predicted. We then deploy the VAE model to the XMM-Newton data of IRAS 13224-3809 and directly estimate, for the first time, the response functions of this source in various observations. The result reveals the corona changing its height between $3~r_{\rm g}$ and $20~r_{\rm g}$, which is correlated with the source luminosity and in line with previous literature. Finally, we discuss the advantages and limitations of this method.

astro-ph.HE↗

arXiv2024

Neutrino Oscillation Effects on the Luminosity of Neutrino-Dominated Accretion Flows Around Black Holes

The stellar-mass black hole surrounded by the neutrino-dominated accretion flow (NDAF) is proposed to be the central engine of the gamma-ray burst (GRB). In this work, we investigate the neutrino/anti-neutrino luminosity and annihilation luminosity from the NDAF and pair-annihilation model, taking into account the neutrino oscillation above the accretion disk. The disk hydrodynamical properties are modelled using the empirical solution previously derived with boundary conditions including the effect of electron degeneracy and neutrino trapping. Our key parameters are the mass accretion rate and the black hole spin given in the range of $\dot{M} = 0.1$ - $10$ $M_\odot$ s$^{-1}$ and $ 0 \le a < 1$, respectively. Without neutrino oscillation, the obtained neutrino/anti-neutrino luminosity is $\sim 10^{51}$ - $10^{53}$ $\textrm{erg s}^{-1}$, while the neutrino annihilation luminosity is found to be $\sim 10^{46}$ - $10^{51}$ $\textrm{erg s}^{-1}$. In the presence of neutrino oscillation in the vacuum limit, the electron neutrino annihilation luminosity decreases by $\lesssim 22\%$ through the flavor transformation, while the muon- and tau-neutrino luminosity can increase up to $\sim 45\%$ and $ 60\%$, respectively. As a result, the total annihilation luminosity can be reduced up to $\sim 19\%$ due to the oscillation process above the disk. Finally, we also investigate the case whereby the CP-violating phase is changed from $δ\textrm{CP} =$ $0^{\circ}$ to $245^{\circ}$. However, our results reveal that the CP-violating phase has minimal impact on neutrino annihilation luminosity.

astro-ph.HE↗

arXiv2022

Mapping the X-ray corona evolution of IRAS 13224-3809 with the power spectral density

We develop the power spectral density (PSD) model to explain the nature of the X-ray variability in IRAS 13224-3809, including the full effects of the X-ray reverberation due to the lamp-post source. We utilize 16 XMM-Newton observations individually as well as group them into three different luminosity bins: low, medium and high. The soft (0.3-1 keV) and hard (1.2-5 keV) PSD spectra are extracted and simultaneously fitted with the model. We find that the corona height changes from h ~ 3 $\ r_{\rm g}$ during the lowest luminosity state to ~ $25 \ r_{\rm g}$ during the highest luminosity state. This provides further evidence that the source height from the reverberation data is significantly larger than what constrained by the spectral analysis. Furthermore, as the corona height increases, the energy spectrum tends to be softer while the observed fractional excess variance, $F_{\rm var}$, reduces. We find that the PSD normalization is strongly correlated with $F_{\rm var}$, and moderately correlated with the PSD bending index. Therefore, the normalization is dependent on accretion rate that controls the intrinsic shape of the PSD. While the intrinsic variability of the disk is manifested by the reverberation signals, the disk and corona may evolve independently. Our results suggest that, during the source height increases, the disk itself generates less overall variability power but more high-frequency variability resulting in the PSD spectrum that flattens out (i.e. the inner disk becomes more active). Using the luminosity-bin data, the hint of Lorentzian component is seen, with the peak appearing at lower frequencies with increasing luminosity.

astro-ph.HE↗

arXiv2022

X-ray timing and spectral analysis of reverberating active galactic nuclei

We use the publicly available XMM-Newton archive to select a sample of 20 active galactic nuclei (AGN) known to exhibit reverberation signatures caused by the reflection of X-rays from the corona off the accretion disc that feeds the central black hole engine. Inverse Compton scattering by energetic electrons, coupled with accretion disc fluctuations give rise to the highly variable observed X-ray spectrum, the behaviour of which is still not fully understood. We use 121 observations in 3 - 4 distinct spectral states for each source and calculate the time lags as a function of frequency. We fit the relativistic reflection model RELXILL and explore parameter correlations. The known scaling relationship between the black hole mass and time lag is well recovered and the continuum flux is coupled strongly to the disc reflection flux. We also find that 1H 0707-495 and IRAS 13224-3809 are well described using reflection and absorption modelling in a variety of flux states. The reflection fraction is strongly coupled to the power law photon index and may be linked to dynamics of the emitting region. The data reveals hints of the power law evolutionary turnover when the 2 - 10 keV Eddington fraction is $\sim0.02$, the origin of which is not fully understood. Finally, we report the covering fraction is inversely correlated with the flux and power law photon index in IRAS 13224-3809. These findings support recent studies of 1H 0707-495 where the covering fraction may contribute to the observed variability via flux modulations from non-uniform orbiting clouds.

astro-ph.HE↗

arXiv2019

Modelling the X-ray power spectra of AGN by using reprocessing echoes from an extended corona

Characteristic signatures that X-ray reverberation from an extended corona can manifest in the observed PSD of AGN are investigated. The presence of two X-ray blobs illuminating an accretion disc can cause the interference between two reprocessing-echo components and produce distinct physical features in the PSD. The oscillatory structures (e.g., dips and humps) are seen but, contrarily to the lamp-post case, the strongest dip is not always the one at the lowest frequency. Instead, we find the frequency where the strongest dip is seen associates to the lower-source height while the lowest frequency where the first dip appears links with the upper-source height. This is because the reverberation timescales increase with the source height. Accurate modelling of the PSD then helps put constraints to the lower and upper limit of the corona extent. Furthermore, the reverberation signatures are less pronounced with increasing number of sources that do not produce reflection (e.g., additional X-rays from fast, relativistic outflows). The amplitude of the oscillations also depends on the amount of dilution contributed by the X-ray sources, thus encodes information about their relative brightness. Due to stronger dilutions, robust detection of these signatures with the current observations will become even more difficult if the corona is extended. Future observations made by Athena will enable us to fit these characteristics in statistically significant details, and to reveal the nature of the disc-corona system.

astro-ph.HE↗