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Chen Deng

Publications and source records attributed to Chen Deng.

At least 19 recordsLinked to original sources
arXiv2026

Signatures of Novikov-Thorne accretion disks around rotating black holes in semiclassical gravity with trace anomaly

Semiclassical gravity provides a promising framework to address the black hole singularity problem through quantum backreaction characterized by a coupling parameter, making it essential to thoroughly explore the accretion properties around such objects. In this paper, within the framework of semiclassical gravity with type-A trace anomaly, we investigate the thermal radiative signatures of Novikov-Thorne accretion disks around rotating black holes across diverse parameter spaces, focusing on the energy flux density, temperature profile, and thermal luminosity. Our findings demonstrate that the introduction of the coupling parameter suppresses disk emission, leading to lower peak values of both energy flux density and temperature, as well as lower peak values and corresponding peak frequencies in thermal luminosity compared to their Kerr counterparts in general relativity. In particular, this discrepancy becomes remarkably pronounced when the black hole possesses a high spin. Mechanistically, increasing the coupling parameter reinforces the effective gravitational field strength of the central compact object, which pushes the equatorial stable circular orbits outward and increases the specific energy of the orbiting matter, thereby reducing the radiative efficiency and weakening the overall disk emission. This suppression mechanism offers a practical astrophysical window to distinguish semiclassical gravity from general relativity and to place observational constraints on the coupling parameter via thermal disk spectra.

gr-qc↗
arXiv2026

A Missing Tool for Calculating Auto/Cross-correlation Function under Nonuniform Sampling Observations

Nonuniform sampling presents a long-standing challenge in astrophysical time-domain analysis, invalidating the standard autocorrelation and cross-correlation functions and forcing researchers to adopt ad-hoc methods like interpolation or binning, which introduce unquantified biases and lack rigorous error estimation. Here we introduce a new method for calculating the nonuniform autocorrelation function (NUACF) and nonuniform cross-correlation function (NUCCF) for irregularly sampled time series. Instead of relying on interpolation, it naturally evaluates the correlation function by incorporating time-interval weights and misalignment penalties. Monte Carlo simulations provide confidence bands for significance assessment and a complete error budget for the time delays that accounts for both flux uncertainties and sampling irregularity (essential but generally absent from existing methods). Through extensive simulations, we demonstrate our method outperforms traditional methods across various conditions, from strictly periodic to complex repeating variability patterns (e.g., intermittent but aperiodic). Its effectiveness is demonstrated via various real astrophysical data sets, revealing repetitive variability in stellar light curves, measuring time delays for multi-band disc reverberation in the AGN Fairall 9, and providing model-independent validation of time delays for the gravitationally lensed quasar HE 0435-1223. The method provides a rigorous and general solution to the ubiquitous problem of nonuniform sampling, positioning it as a useful tool for large-scale time-domain survey data analysis. The framework is also directly applicable to emerging time-domain phenomena such as fast radio bursts (FRBs), enabling, e.g., the study of correlations between persistent radio source luminosity and repeating FRB activity, or among the multi-parameter variability curves of FRB emission itself.

astro-ph.IM↗
arXiv2026

Constraints on the Low-frequency Radio Emission of the Galactic FRB Source SGR 1935+2154

We present a search for radio pulses from the Galactic magnetar SGR 1935+2154, a well-known source of fast radio bursts (FRBs), at $\sim$110 MHz using the Large Phased Array (LPA) of the Pushchino Radio Astronomy Observatory. Data from two active periods in 2020 (March -- May and September -- November, with $\sim 3.5$ minutes of daily coverage) were analyzed with new methods tailored to both FRB-like single pulses and pulsar-like periodic signals. No significant FRB-like pulses were found. Using Monte Carlo simulations, $3σ$ upper limits were derived for the burst rate: for a log-normal energy distribution the limit is $\sim$${10}^{1.5}~{\rm{d}}^{-1}$ for a mean of average monochromatic isotropic luminosity $L_{ν{\rm ,mean}}\sim1.3\times{10}^{29}~{\rm{erg~s^{-1}~ {Hz}^{-1}}}$ and a natural log-space scatter of $σ\sim0.85$; while for a power-law distribution it is $\sim$${10}^{1.8}~{\rm{d}}^{-1}$ for an index $β\lesssim3.0$ and a minimum average monochromatic isotropic luminosity $L_{ν{\rm{,min}}}\lesssim0.7\times{10}^{25}~{\rm{erg~s^{-1}~{Hz}^{-1}}}$. When folded at the known 3.24781628 s period of SGR 1935+2154, a weak pulse was noted (S/N $<$ 3.16), but the significance is insufficient for a secure detection of the pulsar-like emission signal. A conservative upper limit on the average monochromatic isotropic luminosity of any possible periodic emission is $2.08\times{10}^{19}~{\rm{erg~s^{-1}~{Hz}^{-1}}}$. Our results offer meaningful low-frequency upper limits on the burst rate of SGR 1935+2154, and hint for very faint pulsar-like radiation at meter wavelengths.

astro-ph.HE↗
arXiv2026

Decoding FRB Energetics and Frequency Features Hidden by Observational Incompleteness

Fast radio bursts (FRBs) are millisecond-duration extragalactic radio flashes likely powered by magnetars, yet their radiation mechanism remains unknown. Limited sensitivity and finite observing bandwidth inevitably lead to observational truncation, biasing our understanding of intrinsic burst properties. Assuming Gaussian-like spectra, we present a general inverse-modeling framework that reconstructs the intrinsic frequency and energy characteristics of repeating FRBs directly from truncated data, without spectral profile fitting. In our approach, detected bursts are classified as in-band (affected only by the sensitivity cutoff) or band-chipped (affected by both sensitivity and operating-band cutoffs) events. For in-band events, observed and intrinsic quantities are linked through a set of equations. For band-chipped bursts, with spectral peaks possibly outside the telescope's operating band, a population-based method is used to infer individual burst properties from the statistical properties of the entire sample. Applied to 2,223 bursts from FRB 20121102A, it is found that intrinsically energetic bursts tend to have narrower spectra than weak ones. We further quantify, for the first time, the number of out-of-band bursts, and reveal distinct frequency-evolution behaviors across active periods and frequency bands. Comparisons between reconstructed and original samples show that the sensitivity cutoff barely affects burst energy but biases the observed bandwidth, whereas the operating-band cutoff may cause severe energy leakage and bandwidth underestimation, suggesting that the energy release of some repeaters may be underestimated, with potential implications for the energy supply beyond the magnetar magnetosphere. Our methodology transforms incomplete archival observations into physically meaningful probes, bridging instrumental readouts and intrinsic FRB physics.

astro-ph.HE↗
arXiv2026

Diverse Morphologies of GRB X-Ray Plateaus within a Common Magnetar Framework

The origin of the X-ray plateau phase in gamma-ray bursts (GRBs) remains an open problem. In particular, it is unclear whether GRBs with different temporal morphologies (i.e., with a rising, flat, or decaying plateau) arise from a common underlying mechanism. Although magnetar energy injection is a leading explanation, previous studies have primarily inferred magnetar properties on a burst-by-burst basis and have not tested the model at the population level. Here we perform the first hierarchical population inference of magnetar parameters for a uniform sample of 185 long GRBs with X-ray plateaus within a conditional Poisson point-process framework. It is found that the observed plateau population is well reproduced by physically plausible magnetar populations. The inferred parameter distributions show no strong statistical separation among subclasses with different plateau morphologies. Nevertheless, all subclasses show a substantial intrinsic luminosity scatter, $σ_{L,\rm int}\sim0.5$--1.0 dex, whereas the intrinsic duration scatter remains considerably smaller. The results provide a population-level test of the magnetar interpretation of GRB X-ray plateaus, showing that the observed diversity of plateau morphologies does not require distinct magnetar populations.

astro-ph.HE↗
arXiv2026

Constraining the Supernova Remnant Environment of FRB 190520B with Dispersion Measure and Scattering Timescale

FRB 190520B is a repeating fast radio burst source whose large dispersion measure (DM) and temporal broadening suggest a dense and evolving local environment. In this work, we test the possibility that FRB 190520B originates from the core-collapse of a massive star so that its central engine is embedded in a supernova remnant (SNR) expanding into a wind environment, whose evolution is described by the self-similar solution. We use the observed DM and scattering timescale of FRB 190520B to constrain the physical parameters of its surrounding SNR and host-galaxy DM. Twenty typical cases are considered, arising from four ejecta profiles and five scattering prescriptions. It is found that only 6 cases are retained and provide acceptable fits. All retained cases have a shallow ejecta profile and a young source age of $t_0=79.8$--$169.8~{\rm yr}$. The ejecta mass is inferred to be large for all six cases, while the kinetic energy and mass-loss rate span a wide range. The secular DM evolution is reproduced better than the detailed scattering evolution. The up-drift behavior of the scattering residual suggests an additional component or more complicated structures inside the SNR. All retained cases are self-consistent within the adopted scattering theory and the circum-burst medium becomes transparent for GHz bursts before the inferred source ages.

astro-ph.HE↗
arXiv2026

Are Repeaters Prevalent Among the Known Fast Radio Burst Sources?

Fast radio bursts (FRBs) are millisecond radio pulses of unknown origin. Despite extensive follow-up observations, only $\sim3\%$ of FRBs have been confirmed as repeaters. It remains unclear whether the rest are truly one-off bursts, or essentially repeating sources that have only been detected once due to limited monitoring time. Using the second CHIME/FRB catalog, we test this debate by comparing non-repeaters with two repeater-based subsamples: the first-detected bursts of repeaters and their highest-fluence bursts. A non-parametric method that accounts for selection effects is employed to derive the energy functions and event rates of these samples. All samples are well described by broken power-law energy distributions with comparable break energies ($\sim 5\times10^{38}$ erg), but with significantly different slopes between repeating and non-repeating populations. Their event-rate evolution also differs significantly. Assuming $ρ(z) \propto (1+z)^B$, we have $B = -5.57^{+0.15}_{-0.15}$ for non-repeaters and $B = -8.63^{+0.46}_{-0.41}$ and $-9.10^{+0.55}_{-0.56}$ for the two repeater samples. Size-matched resampling shows that the repeater event-rate indices lie far outside the 5$σ$ range expected from non-repeater subsamples, ruling out sample size as the reason for the observed difference. These results indicate that at least a subset of one-off FRBs are intrinsically non-repeating, implying that repeating sources may represent a distinct and possibly less common population.

astro-ph.HE↗
arXiv2026

Construction of an analytic multi-component accretion environment and its application to Kerr black hole imaging

The construction of accretion environments is fundamental to black hole imaging. From a purely geometric perspective, we construct a novel analytic accretion environment comprising a geometrically thick disk, ring-like bumps with a Gaussian profile, and localized compact emission regions modeled by Gaussian distributions. This environment offers high flexibility, enabling independent adjustments of disk thickness, vertical structure, and the positions and morphologies of localized spots, thereby allowing it to qualitatively mimic high-energy astrophysical phenomena. Applying this model to the Kerr spacetime, we investigate the resulting images via radiative transfer and ray-tracing simulations. The results validate the effectiveness of our accretion model and reveal novel observational signatures of Kerr black holes under multi-component illumination, including multiple bright spots and arc-like structures. This work provides a convenient and fully analytic framework for modeling accretion in curved spacetimes, and offers a new perspective on inferring accretion mechanisms and transient high-energy processes from image features.

gr-qc↗
arXiv2026

Rational Orbits and Gravitational Waves in Static Spherical Spacetimes: An Open-Source Numerical Framework

Timelike orbits constitute a crucial probe for exploring the intrinsic properties of curved spacetimes, and the carried gravitational radiation signals provide a direct window into strong field gravity. In this paper, we develop a versatile computational framework based on Mathematica and the OpenMP parallel architecture to simulate the rational orbits of timelike particles and their gravitational radiation in static spherically symmetric spacetimes. Specifically, requiring only the user defined covariant metric, this numerical tool can efficiently calculate rational orbits across various configurations, as well as the corresponding gravitational wave polarization states and characteristic strains. The package presented here offers a highly efficient and comprehensive one-stop solution for investigating the properties of curved spacetimes and their potential observational signatures. To demonstrate the reliability and capability of our code, we apply it to the Schwarzschild spacetime as a test case, illustrating the functionality of the code across several key aspects, including the effective potential, stable orbital regions, rational and irrational orbits, and gravitational wave signals. Furthermore, we show that the gravitational waves emitted by an extreme-mass-ratio inspiral system composed of an intermediate mass black hole and the Galactic Center supermassive black hole have the potential to be identified by future space detectors.

gr-qc↗
arXiv2026

Reshaping the inner shadow of a Kerr black hole by a torn accretion disk

When an accretion flow extends to the event horizon, their intersection defines the contour of the inner shadow. However, the morphological evolution of this critical feature remains largely unexplored within a torn accretion disk system, a configuration comprising distinct sub-disks formed when a tilted disk is disrupted by frame-dragging. To address this, we phenomenologically construct a torn accretion disk model and numerically simulate the inner shadow of a Kerr black hole using relativistic backward ray-tracing. We discover that the torn disk geometry profoundly alters the black hole's observational signatures, inducing severe erosion of the inner shadow and generating novel features such as bifurcated shadows, crescent-like structures, and multiple orders of shadow rings. These exotic morphologies, which are predominantly governed by the spatial discontinuity between the sub-disks and the tilt angle of the outer sub-disk, are exceedingly difficult to replicate within standard equatorial accretion paradigms. Our findings demonstrate that these distinctive shadow structures hold significant potential to serve as robust diagnostic probes for torn accretion environments, simultaneously implying that relying solely on the inner shadow to test gravity theories is fundamentally insufficient.

gr-qc↗
arXiv2026

A second-scale periodicity in an active repeating fast radio burst source

Fast radio bursts (FRBs) are fierce radio flashes from the deep sky. Abundant observations have indicated that highly magnetized neutron stars might be involved in these energetic bursts, but the underlying trigger mechanism is still enigmatic. Especially, the widely expected periodicity connected to the spin of the central engine has never been discovered, which leads to further debates on the nature of FRBs. Here we report the first discovery of a $\sim$ 1.7 s period in the repeating source of FRB 20201124A. This is an active repeater, from which more than 2800 bursts have been detected over a total of 49 days. The phase-folding method is adopted to analyze the bursts on each day separately. While no significant periodic signal is found in most days, a clear periodicity does appear on two specific days: a period of 1.706024(13) s on MJD 59310, and a slightly larger period of 1.707968(9) s on MJD 59347. A global Monte Carlo analysis based on all single-day datasets yields a significance level of $5.5 σ$ for the periodicity. A period derivative of $6.11(5)\times10^{-10}$ s s$^{-1}$ can be derived from these two periods, which further implies a surface magnetic field strength of $1.03\times10^{15}$ G and a spin-down age of $44$ years for the central engine. It is concluded that FRB 20201124A should be associated with a young magnetar.

astro-ph.HE↗
arXiv2026

NeSy-CSA: A Neuro-Symbolic Framework for Open-Ended Critical Scenario Attribution

Understanding why discovered scenarios become critical in scenario-based testing is essential for effectively leveraging them in decision-making systems. Reasoning about such criticality can be formulated as an attribution problem. However, across different decision-making tasks, the causes of criticality may involve diverse state variables, interaction patterns, and failure mechanisms, making attribution an inherently open-ended problem beyond predefined explanation spaces. Existing attribution methods still struggle to balance open-ended reasoning flexibility with the interpretability and traceability required for critical scenario reasoning. To address this limitation, we propose NeSy-CSA, a neuro-symbolic framework that transforms open-ended critical scenario attribution from unconstrained explanation generation into structured and traceable reasoning. NeSy-CSA narrows the attribution space by selecting relevant factors, makes the reasoning process traceable through a dependency-aware evidence graph, and executes symbolic reasoning procedures derived from atomic operations, coordinated with evidence-constrained neural inference to support flexible open-ended attribution. We further introduce a process-level and result-level assessment module to evaluate the structural validity of the attribution process and the behavioral effectiveness of the attribution results under controlled interventions. Experiments across four decision-making environments show that NeSy-CSA improves two intervention-based measures of attribution effectiveness by 18.32% and 13.67% over LLM-based baselines. These results demonstrate its potential to transform discovered critical scenarios into reusable knowledge for subsequent testing and safety analysis.

cs.LG↗
arXiv2026

Gravitational emissions and light curves of quasi-periodic orbits in Schwarzschild spacetime embedded in a Dehnen-type dark matter halo

Timelike orbits in curved spacetimes encode intrinsic information about the background geometry and serve as critical probes for investigating gravitational theories and source distributions. In this study, we investigate strictly closed timelike orbits within a Schwarzschild spacetime embedded in a Dehnen-type dark matter halo. By solving the geodesic equations, we identify various configurations of these closed orbits and simulate their corresponding gravitational waves and electromagnetic light curves. Our findings reveal that the morphology of closed orbits is primarily governed by the ratio of the azimuthal period to the radial period. Notably, dark matter halo parameters such as the core scale and density parameters exert a significant amplification effect on the orbital scale, which further induces a discernible phase lag in the gravitational wave signals. Furthermore, within a specific parameter space, we discover a linear relationship between the number of peaks in the light curves and the number of orbital leaves. From a theoretical perspective, these findings reveal the multimessenger signatures of closed orbits, which may provide a potential theoretical foundation for establishing a connection between orbital dynamics and the surrounding dark matter environment.

gr-qc↗
arXiv2026

Gamma-Ray Bursts: Evidence for a Common Origin of X-ray Plateaus with Diverse Temporal Decay Index

A significant fraction of gamma-ray bursts (GRBs) exhibit a plateau in the early X-ray afterglow light curve, whose mechanism remains uncertain. While the post-plateau normal decay index ($α_2$) is commonly used to constrain the afterglow dynamics, the shallow-decay slope of the plateau itself ($α_1$) has received comparatively little attention. Recent observations, however, reveal substantial dispersion in $α_1$, raising the question of whether GRBs with rising, flat and mildly decaying plateaus represent intrinsically distinct populations. To address this question, we collect a uniform sample of 185 $\textit{Swift}$ GRBs with a well-defined plateau and divide them into three groups based on $α_1$. Using a non-parametric approach, we reconstruct their X-ray luminosity functions, redshift distributions and event rates. It is found that the three groups exhibit statistically consistent properties across all diagnostics, with no evidence for group-specific features. Monte Carlo perturbation tests further show that these results are insensitive to the adopted classification boundaries of $α_1$. Our results indicate that variations in the plateau slope $α_1$ do not define distinct GRB subclasses, but instead the sample constitutes a statistically uniform population governed by a common framework.

astro-ph.HE↗
arXiv2026

Modeling the Multi-Wavelength Afterglow of Short Gamma-Ray Bursts with a Plateau Phase

Short gamma-ray bursts (GRBs) exhibiting a plateau phase provide valuable insights into the post-merger activity of their central engines. Although the physical origin of the plateau remains uncertain, the magnetar energy injection model offers a compelling explanation that reproduces the observed temporal and luminosity features. However, previous studies relying solely on X-ray data have suffered from strong parameter degeneracies when constraining the magnetar parameters. Here we perform broadband afterglow modeling on seven short GRBs with plateau features by combining X-ray, optical, and radio observations within the framework of the magnetar energy injection model. Key model parameters are derived by using the Markov Chain Monte Carlo method. It is found that the energy injection substantially modifies the afterglow dynamics in most events. Compared with X-ray-only analyses, our broadband modeling yields systematically a lower magnetic field strength and a shorter spin period for the central magnetar, corresponding to a higher injection luminosity. The study clearly shows that incorporating multi-wavelength data effectively alleviates the degeneracy between the magnetar parameters and X-ray radiative efficiency. In addition, the distribution of our short GRBs differs markedly from long GRBs when they are plotted on the initial Lorentz factor versus gamma-ray energy plane. This offset, consistent with the observed harder spectrum of short GRBs, may serve as a useful diagnostic for investigating the progenitor as larger samples are available.

astro-ph.HE↗
arXiv2026

Statistical analysis of multi-band plateaus in gamma-ray burst afterglows

Plateau features are frequently observed in the afterglows of gamma-ray bursts (GRBs), yet their physical origins remain under debate. In this work, we compile a sample of 124 GRBs with known redshifts and simultaneous X-ray and optical afterglow observations. We categorize them into four subsets based on the existence of plateaus and the bands in which they appear. Namely, Dataset 1: plateaus are detected simultaneously in both X-ray and optical bands (75 bursts); Dataset 2: plateaus are only in X-rays (15 bursts); Dataset 3: plateaus appear only in the optical (17 bursts); Dataset 4: no plateaus in either band (17 bursts). We employ these datasets to test the applicability of the energy-injection model by examining whether the temporal decay index $α$ and the spectral index $β$ of GRB afterglows simultaneously satisfy the closure relations in X-ray and optical bands. We find that 47 bursts of Dataset 1 simultaneously obey the closure relations in both bands under the conditions of the electron spectral index $p>2$ and the injection parameter $q\in (0, 0.5)$, and 69 of the dataset for $p>1$ and $q\in (0, 0.8)$, providing a strong support for the energy-injection interpretation. However, for Datasets 2 and 3, although $α$ and $β$ of the plateaus mostly satisfy the closure relations, those in the other band show significant deviations, which implies that bursts with a single-band plateau are inconsistent with the interpretation of energy injection. Furthermore, we also compare the isotropic X-ray energy of plateaus with the rotational energy budget of millisecond magnetars.

astro-ph.HE↗
arXiv2025

A Statistical Analysis of Fluence and Energy Distributions of Non-repeating Fast Radio Bursts Detected by CHIME

Fast Radio Bursts (FRBs) are energetic radio bursts that typically last for milliseconds. They are mostly of extragalactic origin, but the progenitors, trigger mechanisms and radiation processes are still largely unknown. Here we present a comprehensive analysis on 415 non-repeating FRBs detected by CHIME, applying manual filtering to ensure sample completeness. It is found that the distribution of fluence can be approximated by a three-segment power-law function, with the power-law indices being $-3.76 \pm 1.61$, $0.20 \pm 0.68$ and $2.06 \pm 0.90$ in the low, middle, and high fluence segments, respectively. Both the total dispersion measure (\text{DM}) and the extragalactic \text{DM} follow a smoothly broken power-law distribution, with characteristic break DM values of $\sim 703$ pc $\rm cm^{-3}$ and $\sim 639$ pc $\rm cm^{-3}$, respectively. The redshifts are estimated from the extragalactic \text{DM} by using the Macquart relation, which are found to peak at $ z \sim 0.6$. The isotropic energy release ($E_{\text{iso}}$) is also derived for each burst. Two-Gaussian components are revealed in the distribution of $E_{\text{iso}}$, with the major population narrowly clustered at $\sim 2.3 \times 10^{40} {\rm erg}$. The minor population have a characteristic energy of $\sim 1.6 \times 10^{39}$ erg and span approximately one order of magnitude. The distribution hints a near-uniform energy release mechanism for the dominant population as expected from some catastrophic channels, whereas the lower-energy component (potentially including repeat-capable sources) may reflect a broader diversity in FRB origins, emission mechanisms and evolutionary stages.

astro-ph.HE↗
arXiv2025

A Statistical Study of the Gamma-Ray Burst and Supernova Association

The association between long gamma-ray bursts (LGRBs) and core-collapse supernovae (SNe) has been well established since the discovery of SN 1998bw, which was linked to the low-luminosity LGRB 980425. However, long-term monitoring of several well-localized, low-redshift LGRBs has yielded compelling evidence for the absence of accompanying SNe. Notably, two long bursts, GRB 211211A and GRB 230307A, show signatures consistent with kilonova emission from compact binary mergers, indicating that at least some long events may originate from progenitors other than core-collapse SNe. In this study, we conduct a comparative analysis of two samples of LGRBs, i.e., LGRBs with and without SN associations, to investigate the differences that may reveal intrinsic distinctions in their progenitors. A detailed examination of their prompt emission properties, host galaxy environments, and event rates is performed. While the two samples exhibit considerable overlap in most observed properties, a significant discrepancy in their event rate is revealed. LGRBs without SN association have an event rate that aligns well with the star formation rate, whereas that of SN-associated LGRBs differs significantly. It indicates that LGRBs without an SN association may constitute a distinct subclass with intrinsically different progenitors.

astro-ph.HE↗