arXiv subjects

Zamri Zainal Abidin

Publications and source records attributed to Zamri Zainal Abidin.

14 recordsLinked to original sources

arXiv2026

Compton-thick AGN Characterisation in a Multi-wavelength Context: Insights from the 70-Month \textit{SWIFT}/BAT Catalogue

We analyse Compton-thick active galactic nuclei (CT AGNs), a heavily obscured subclass that challenges traditional X-ray diagnostics. Using 243 sources from the 70-Month \textit{SWIFT}/BAT catalogue (26 CT, 217 non-CT), we investigate their properties across radio, infrared (IR), optical, and X-ray bands. VLASS data reveals slightly higher 2--3~GHz mean luminosities in CT AGNs, suggesting active cores attenuated by circumnuclear absorption. Mid-IR diagnostics show redder $W3-W4$ colours in CT AGNs, tracing cooler dust, with significant scatter likely driven by host-galaxy dilution. Most CT AGNs fall outside standard WISE selection wedges, highlighting mid-IR selection limitations. BPT diagnostics show that CT AGNs primarily occupy Seyfert regions, indicating isotropic narrow-line properties. CT AGNs favour significantly higher Eddington ratios ($λ_{\text{Edd}}$), supporting radiation-driven unification where intense accretion maintains high-column density. We also observe a moderate anti-correlation between [NII]/H$α$ and $λ_{\text{Edd}}$. Principal component analysis identifies ionizing power and the accretion-obscuration link as primary variance drivers, though both populations overlap significantly in the PC1--PC2 plane. Machine learning achieved high recall (0.80) using intrinsic X-ray luminosity, [OI]$λ$6300 and H$α$ luminosities, and $W2-W3$ colour. This demonstrates the potential for multi-wavelength signatures to verify CT candidates in future deep surveys where X-ray data is limited. Overall, our findings suggest CT AGNs are driven by high obscuration and accretion rates rather than a simple orientation effect.

astro-ph.GA↗

arXiv2026

F10.7 Index Prediction: A Multiscale Decomposition Strategy with Wavelet Transform for Performance Optimization

In this study, we construct Dataset A for training, validation, and testing, and Dataset B to evaluate generalization. We propose a novel F10.7 index forecasting method using wavelet decomposition, which feeds F10.7 together with its decomposed approximate and detail signals into the iTransformer model. We also incorporate the International Sunspot Number (ISN) and its wavelet-decomposed signals to assess their influence on prediction performance. Our optimal method is then compared with the latest method from S. Yan et al. (2025) and three operational models (SWPC, BGS, CLS). Additionally, we transfer our method to the PatchTST model used in H. Ye et al. (2024) and compare our method with theirs on Dataset B. Key findings include: (1) The wavelet-based combination methods overall outperform the baseline using only F10.7 index. The prediction performance improves as higher-level approximate and detail signals are incrementally added. The Combination 6 method integrating F10.7 with its first to fifth level approximate and detail signals outperforms methods using only approximate or detail signals. (2) Incorporating ISN and its wavelet-decomposed signals does not enhance prediction performance. (3) The Combination 6 method significantly surpasses S. Yan et al. (2025) and three operational models, with RMSE, MAE, and MAPE reduced by 18.22%, 15.09%, and 8.57%, respectively, against the former method. It also excels across four different conditions of solar activity. (4) Our method demonstrates superior generalization and prediction capability over the method of H. Ye et al. (2024) across all forecast horizons. To our knowledge, this is the first application of wavelet decomposition in F10.7 prediction, substantially improving forecast performance.

astro-ph.IM↗

arXiv2026

Prediction of Major Solar Flares Using Interpretable Class-dependent Reward Framework with Active Region Magnetograms and Domain Knowledge

In this work, we develop, for the first time, a supervised classification framework with class-dependent rewards (CDR) to predict $\geq$MM flares within 24 hr. We construct multiple datasets, covering knowledge-informed features and line-of sight (LOS) magnetograms. We also apply three deep learning models (CNN, CNN-BiLSTM, and Transformer) and three CDR counterparts (CDR-CNN, CDR-CNN-BiLSTM, and CDR-Transformer). First, we analyze the importance of LOS magnetic field parameters with the Transformer, then compare its performance using LOS-only, vector-only, and combined magnetic field parameters. Second, we compare flare prediction performance based on CDR models versus deep learning counterparts. Third, we perform sensitivity analysis on reward engineering for CDR models. Fourth, we use the SHAP method for model interpretability. Finally, we conduct performance comparison between our models and NASA/CCMC. The main findings are: (1)Among LOS feature combinations, R_VALUE and AREA_ACR consistently yield the best results. (2)Transformer achieves better performance with combined LOS and vector magnetic field data than with either alone. (3)Models using knowledge-informed features outperform those using magnetograms. (4)While CNN and CNN-BiLSTM outperform their CDR counterparts on magnetograms, CDR-Transformer is slightly superior to its deep learning counterpart when using knowledge-informed features. Among all models, CDR-Transformer achieves the best performance. (5)The predictive performance of the CDR models is not overly sensitive to the reward choices.(6)Through SHAP analysis, the CDR model tends to regard TOTUSJH as more important, while the Transformer tends to prioritize R_VALUE more.(7)Under identical prediction time and active region (AR) number, the CDR-Transformer shows superior predictive capabilities compared to NASA/CCMC.

cs.LG↗

arXiv2026

Investigating Ionospheric TEC Variations in Solar and Geomagnetic Influences Across Solar Activity Phases

This study examines the variability of ionospheric total electron content (VTEC) in response to solar and geomagnetic drivers across solar cycles 23 to 25. While the dominant effect of solar radiation on VTEC is well-known, a comprehensive understanding of how these relationships and their time-lags vary across distinct solar cycle phases and across cycles of differing intensity has been lacking. Using global VTEC data from the Chinese Academy of Sciences Global Ionospheric Maps (CASG) and solar-geophysical indices from NASA's OMNI dataset spanning from 1998 to 2025, this study bridges that gap by quantifying correlation strengths and time-lag relationships between VTEC and parameters such as $F_{10.7}$ solar flux, R sunspot number, Kp, Ap, and Dst indices, and solar wind properties. Results show that solar proxies, particularly $F_{10.7}$ and R sunspot number, exhibit the strongest, most consistent correlations with VTEC, especially during the ascending and descending phases of the solar cycle, with a characteristic $\sim2$-day lag attributed to thermospheric oxygen dynamics and ionospheric recombination processes. In contrast, geomagnetic indices exhibit weaker and phase-dependent correlations, while direct correlations between solar wind parameters and global VTEC are weak, as their influence is primarily mediated by geomagnetic activity and exhibits strong regional and temporal heterogeneity. Phase-resolved analyses further reveal that geomagnetic activity plays a more prominent role during transitional phases, while maximum and minimum periods are dominated by EUV variability and non-solar drivers, respectively. These findings highlight the necessity of incorporating solar phase and time-lag dependencies in ionospheric modelling and forecasting efforts.

astro-ph.SR↗

arXiv2026

Operational Solar Flare Forecasting System Using an Explainable Large Language Model

This study focuses on forecasting major (>=M-class) solar flares that can severely impact the near-Earth environment. We construct two types of datasets using the Space Weather HMI Active Region Patches (SHARP), and develop a flare prediction network based on large language model (LLMFlareNet). We apply SHapley Additive exPlanations (SHAP) to explain the model predictions. We develop an operational forecasting system based on the LLMFlareNet model. We adopt a daily mode for performance comparison across various operational forecasting systems under identical active region (AR) number and prediction date, using daily operational observational data. The main results are as follows. (1) Through ablation experiments and comparison with baseline models, LLMFlareNet achieves the best TSS scores of 0.720 +/- 0.040 on the ten cross-validation (CV) dataset with mixed ARs. (2) By both global and local SHAP analyses, we identify that R_VALUE is the most influential physical feature for the prediction of LLMFlareNet, aligning with flare magnetic reconnection theory. (3) In daily mode, LLMFlareNet achieves TSS scores of 0.680/0.571 (0.689/0.661, respectively) on the dataset with single/mixed ARs, markedly outperforming NASA/CCMC (SolarFlareNet, respectively). This work introduces the first application of a large language model as a universal computation engine with explainability method in this domain, and presents the first comparison between operational flare forecasting systems in daily mode. The proposed LLMFlareNet-based system demonstrates substantial improvements over existing systems.

astro-ph.SR↗

arXiv2025

Temporal variability in low-frequency radio interference: Insight from high-cadence monitoring at a candidate radio notification zone in Malaysia

Extensive radio frequency interference (RFI) monitoring is essential in the site selection process before constructing radio astronomy observatories, followed by mitigation strategies to minimize its adverse effects. Malaysia has an enormous prospect for radio astronomy due to its prominent location in the centre of Southeast Asia, but is challenged by its relatively high population density. In this research article, we perform high-cadence, low-frequency RFI monitoring at two sites, each representing an urban and a rural environment. Using modified generalized spectral kurtosis (GSK) as an RFI detection method, we ascertain the suitability of Glami Lemi, a rural area in the centre of Peninsular Malaysia previously assigned as a candidate radio notification zone (RNZ), as a potential site for radio astronomy observations due to its lower RFI contamination in our high-cadence monitoring, especially when compared with urban areas. We identified a number of persistent and transient RFI in our dataset, associate each of them with their potential origins and, if present, characterize their temporal evolution. A few types of RFI mitigation strategies were also tested and discussed. This study lays the groundwork for Malaysia's endeavours in establishing its first research-grade radio telescope, emphasizing the importance of robust RFI detection and mitigation strategies in optimizing observational outcomes.

astro-ph.IM↗

arXiv2025

Investigating the Jet Width Profile of CTA 102 with Very Long Baseline Interferometry at Parsec Scales

Active Galactic Nucleus jets have long be thought to exhibit a conical jet shape, but recently, several jets were found to have a transition from parabolic to conical structure. As more sources are investigated, this collimation profile appears to represent a common paradigm. Previous works suggest that the Bondi radius may serve as an indicator of the transition location, although discrepancies have been observed in some sources. To explore this further, we selected CTA 102 for which existing literature presents mixed evidence regarding the presence of a jet geometry break. We investigated the jet width profile of CTA 102 to study the possible transition changes in the jet, thereby improving the understanding of connection between Bondi radius and jet transition. We used multi-frequency VLBA images of CTA 102 at 2, 5, and 8 (single epoch), and 15, 22 and 43 GHz (stacked). The jet width profile was modeled with a single power law $W_{jet}\propto r^ε$ yielding a power-law index of $ε=0.69\pm0.02$, indicative of a quasi-parabolic geometry with no clear transition to a conical regime. The absence of discernible structural break around the Bondi radius implies that the physical conditions associated with the radius alone are insufficient to explain the jet collimation behaviour. On the other hand, we observe oscillatory features in the jet width profile, suggesting the influence of additional physical processes beyond gravitational confinement. These findings contribute to a more nuanced understanding of jet collimation in AGN and highlight the complexity of jet-environment interactions.

astro-ph.HE↗

arXiv2025

Rethinking Habitability using Biogenic Precursors: Formaldehyde in Millimeter Molecular Clouds of the Inner Galaxy

We present a comprehensive study of formaldehyde (H2CO) absorption and radio recombination line (H110a) emission in 215 molecular clouds from the Bolocam Galactic Plane Survey (BGPS), observed using the Nanshan 25-m radio telescope. H2CO was detected in 88 sources (40.93 percent) with 59 being new detections, while H110a emission was found in only 11 sources (5.12 percent), all coincident with H2CO absorption. There exists a correlation of H2CO fluxes with millimeter fluxes below a 3 Jy threshold and an increased dispersion above it, suggesting the sub-CMB cooling of H2CO. Cross-matching with kinematic distance catalogs revealed H2CO spanning galactocentric distances from 0.216 to 10.769 kpc, with column densities ranging from 7.82 x 10^11 to 6.69 x 10^14 cm-2. A significant inverse correlation was observed between H2CO detection fraction and galactocentric distance, suggesting enhanced star forming activity closer to the Galactic Center. These findings challenge traditional Galactic Habitable Zone (GHZ) models by demonstrating the presence of biogenic precursors in the inner Galaxy, shielded within dense molecular clouds. Our results underscore the importance of incorporating chemical tracers like H2CO, alongside physical constraints, to refine the boundaries of the GHZ and advance the research of prebiotic chemistry in the Milky Way.

astro-ph.GA↗

arXiv2023

The Limits of Water Maser Kinematics: Insights from High-Mass Protostar AFGL 5142-MM1

Multi-epoch VLBI observations measure 3D water maser motions in protostellar outflows, enabling analysis of inclination and velocity. However, these analyses assume that water masers and shock surfaces within outflows are co-propagating. We compared VLBI data on maser-traced bowshocks in high-mass protostar AFGL 5142-MM1, from seven epochs of archival data from the VLBI Exploration of Radio Astrometry (VERA), obtained from April 2014 to May 2015, and our newly-conducted data from the KVN and VERA Array (KaVA), obtained in March 2016. We find an inconsistency between the expected displacement of the bowshocks and the motions of individual masers. The separation between two opposing bowshocks in AFGL 5142-MM1 was determined to be $337.17\pm0.07~\rm{mas}$ in the KaVA data, which is less than an expected value of $342.1\pm0.7~\rm{mas}$ based on extrapolation of the proper motions of individual maser features measured by VERA. Our measurements imply that the bowshock propagates at a velocity of $24\pm3~\rm{km~s^{-1}}$, while the individual masing gas clumps move at an average velocity of $55\pm5~\rm{km~s^{-1}}$, i.e. the water masers are moving in the outflow direction at double the speed at which the bowshocks are propagating. Our results emphasise that investigations of individual maser features are best approached using short-term high-cadence VLBI monitoring, while long-term monitoring on timescales comparable to the lifetimes of maser features, are better suited to tracing the overall evolution of shock surfaces. Observers should be aware that masers and shock surfaces can move relative to each other, and that this can affect the interpretation of protostellar outflows.

astro-ph.SR↗

arXiv2021

A comprehensive analysis using 9 dark matter halo models on the spiral galaxy NGC 4321

This paper addressed the dark matter analysis on the spiral galaxy NGC 4321 (M100) by considering the nine different dark matter profiles so far lacking in the scientific literature, i.e. Pseudoisothermal, Burkert, NFW, Moore, Einasto, core-modified, DC14, coreNFW and Lucky13 profiles. In this paper, we analyzed the rotation curve analysis on the galaxy NGC 4321 by using nonlinear fitting of star, gaseous and dark matter halo equations with selected VLA HI observation data. Among the nine dark matter profiles, four dark matter profiles (DC14, Lucky13, Burkert and Moore profiles) showed declining features and hence found to be not suitable for this galaxy. This is concluded to be mainly due to the characteristics of those dark matter profiles and also due to the varying levels of problems within the inner regions fittings. For the remaining five accepted dark matter profiles, we further conducted analysis by using the reduced chi-square test. Four out of the five accepted dark matter profiles lie within the range of 0.40 < reduced chi-square < 1.70, except for the case of the core-modified profile. In addition, Pseudoisothermal profile achieved the best fitting i.e. reduced chi-square nearest to 1, mainly due to its linearity in the inner region and flatness at large radii.

astro-ph.GA↗

arXiv2018

Dark Matter in the Central Region of the Spiral Galaxy NGC 4321

We present our results of 12 CO(1-0) transition in the central region of NGC 4321 using the Atacama Large Millimeter and Sub-millimeter Array (ALMA). We found an unaccounted mass of $2.3 \times 10^9 M_{\odot}$ within the central 0.7 kpc of this galaxy. The expected mass of the supermassive black hole (SMBH) in this galaxy is much smaller than the unaccounted mass. The invisible mass is likely caused by dark matter in the central region of the galaxy, indicating a cuspy dark matter profile. We also investigated the Modified Newtonian Dynamics (MOND) as an alternative mechanism to explain the invisible mass. We noted that at the radius of 0.7 kpc of the galaxy, the acceleration is about $1.04 \times 10^-7~cm~s^-2$, which is much larger than the critical acceleration $a_{0} \sim 1.2 \times 10^-8 ~cm~s^-2$ in the MOND theory, suggesting that theory might not be able explain the unseen mass problem in central region of this galaxy.

astro-ph.GA↗

arXiv2018

Dark Matter in the Central Region of NGC 3256

We investigated the central mass distribution of the luminous infrared galaxy NGC 3256 at a distance of 35 Mpc by using CO(1-0) observations of the Atacama Large Millimeter and sub-millimeter Array (ALMA) and near-IR data of the Two Micron Sky Survey (2MASS). We found that there is a huge amount of invisible dynamical mass ($4.84 \times 10^{10} M_{\odot}$) in the central region of the galaxy. The invisible mass is likely caused by some dark matter, which might have a cuspy dark matter profile. We note that this dark matter is difficult to explain with the conventional Modified Newtonian Dynamics (MOND) model, which is only applicable at a low acceleration regime, whereas the acceleration at the central region of the galaxy is relatively strong. Therefore, this discovery might pose a challenge to the conventional MOND models.

astro-ph.GA↗

arXiv2015

Supernova Neutrino Background Bound on the SFR History

The purpose of the present study is to compare the predictions of different models of star formation rate (SFR) history in the universe with the upper limit of Super Kamiokande for the neutrino background. To this aim we have calculated the expected neutrino density for the most popular models of SFR history, Hogg et al. ,Glazebrook et al., Cole et al., Yuksel et al., Hernquist et al. and Kaplinghat et al. Differerent from previous studies we have used the $Λ$CDM model with $Ω_Λ = 0.7$. We have assumed that the detector used for the detection the neutrino flux is SuperK and also we have assumed that the electron neutrinos produced in the Supernovae oscillate equally to the three standard model flavors. By these assumptions all models stay below the upper limit of SuperK on the event rate and the detection of the supernova relic neutrino background (SRNB) remains undetected. Future neutrino detectors such as KM3Net will be able to detect the SRNB and distinguish between the models of the SFR history.

astro-ph.HE↗

arXiv2014

Rotation Curve with MOND and Dark Matter Halo profile for ESO138-G014

This paper is devoted to solve the galactic rotation problem for ESO138-G014 galaxy based on two theories: dark matter and Modified Newtonian Dynamics. Here we did the rotation curve analysis with two possible choices for the dark matter density profile, namely Burkert and Navarro, Frenk and White profiles. The analysis shows the dark matter distribution favored to Burkert profile (cored dark matter). The standard hypothesis for most spiral galaxies are known to be embedded in dark matter haloes has now been overshadowed by Modified Newtonian Dynamics, known as MOND, the leading alternative of dark matter. MOND addresses the problem of a new fundamental constant $a_0$, called the acceleration constant, at which acceleration scale of Newton second law fails to hold. In this respect, we investigate this issue by testing the rotation curve within the MOND framework with the observations to obtain the reliable disk mass, $M_D$. We investigate whether ESO138-G014 is compatible with MOND or dark matter is still favorable for the galactic rotation problem.

astro-ph.GA↗