arXiv subjects

Sujie Lin

Publications and source records attributed to Sujie Lin.

12 recordsLinked to original sources

arXiv2026

Reconstruction of Shower-like Events in NEON Using Likelihood and Graph Neural Network Methods

The Neutrino Observatory in the Nanhai (NEON) is a proposed deep-sea neutrino telescope deployed in the South China Sea. Accurate reconstruction of shower-like events is crucial for neutrino energy measurements and multi-messenger astronomy, yet it poses significant challenges due to seawater optical attenuation, irregular detector geometry, and substantial $^{40}\mathrm{K}$ ambient background. In this work, we present the first comprehensive reconstruction framework for shower-like events in NEON, encompassing both a physics-driven maximum likelihood estimation (MLE) method and a data-driven Graph Neural Network (GNN). The traditional MLE framework integrates spatial-isochronic hit selection, vertex reconstruction via time-residual M-estimator minimization, and decoupled directional and energy estimation based on pre-computed photon distribution tables. Physical calibrations, including PMT angular acceptance, hit-level time slewing corrections, and an effective line-source shower extension, are incorporated into the likelihood formulation. In parallel, a two-stage GNN is developed to capture intra-DOM PMT correlations and distance-weighted inter-DOM topological patterns. Simulation studies show that the MLE method achieves an overall median angular resolution of $4.19^\circ$ and an energy resolution of 25\%-37\% over 1 TeV to 1 PeV with negligible systematic bias. The GNN further improves reconstruction fidelity in the low-to-intermediate energy regime, achieving a median angular resolution of $1.8^\circ$ at 30 TeV and an energy resolution of $\sim$ 20\% between 40 and 300 TeV. Based on these reconstruction performances, the effective area and point-source discovery potential of NEON are evaluated. This framework establishes an essential reconstruction benchmark for NEON and provides practical methodologies for future next-generation deep-sea neutrino telescopes.

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arXiv2026

Risk assessment of muon single-event effects for low-altitude aircraft

With the rapid development of low-altitude economy, the radiation environment safety of low-altitude aircraft such as drones and electric vertical take-off and landing aircraft has attracted increasing attention. Although the dense lower atmosphere traditionally serves as an effective shield against cosmic radiation, the shrinking feature sizes of modern integrated circuits greatly enhance their vulnerability to single-event effects (SEEs). This study quantitatively evaluates muon-induced SEE risks for low-altitude aircraft in various regions of China under both static cosmic-ray background and ground-level enhancement (GLE) events, aiming to provide critical guidance for the next-generation low-altitude aviation platforms.Using city-specific atmospheric models within the CORSIKA framework, we simulate atmospheric shower processes and obtain reliable energy spectra for low-energy muons (10-100 MeV). We also employ simulation data from other research groups to estimate muon-induced SEE cross sections for transistors at different process nodes, including bulk, FD-SOI, and FinFET technologies. By incorporating solar energetic particle spectra associated with GLE events, we assess muon-induced SEE risks under both static and GLE conditions. Our results show that under static conditions, flight control systems with 1 MB memory using advanced nodes below 45 nm and bulk transistors face non-negligible muon-induced SEE risks in all Chinese cities. In contrast, systems with FD-SOI transistors can effectively mitigate these risks. For large-memory systems (1 GB), redundancy or other hardening measures are essential regardless of the process technology. Regarding GLE events, we introduce the concept of muon hazard levels to evaluate regional risk variations. During GLEs, the increase in muon-induced SEE risk is negligible in mid-to-low latitude regions but becomes significant at high latitudes.

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arXiv2026

Data-driven modeling of Galactic diffuse emission with multi-wavelength observations

We present a data-driven investigation of Galactic diffuse emission. Using multi-frequency Planck radio/microwave maps (30-857 GHz) and Fermi-LAT gamma-ray data (50 MeV-814 GeV), we construct a nonlinear mapping between radio emission and gamma-ray intensity through supervised machine learning. Our models achieve high predictive accuracy (R^2 > 0.90 in the 0.1-10 GeV range), demonstrating that multi-frequency radio observations encode sufficient information to reconstruct both spatial morphology and spectral properties of diffuse gamma-ray emission. By analyzing model performance across different frequency bands and spatial regions, we identify high-frequency radio bands as the dominant predictor, providing direct empirical support for the hadronic origin of Galactic 0.1-10 GeV gamma rays, while low-frequency radio bands for the leptonic origin above 10 GeV. Residual maps reveal coherent large-scale structures, including Loop I and III, highlighting regions where standard interstellar emission models are incomplete or biased. Compared with the GALPROP model, our machine learning approach yields a higher R^2=0.95 and lower mean absolute relative error (14.7%) in the inner Galactic disk and the Galactic center region. Our results illustrate that machine learning serves as a physically interpretable tool for multi-messenger astrophysics, providing a data-driven baseline for separating non-standard emission components and deriving new constraints on cosmic-ray propagation and interstellar medium structure.

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arXiv2026

Collective Winds of Massive Star Clusters as the Dominant PeVatrons for Galactic Cosmic Rays

The knee feature in the cosmic-ray energy spectrum around 4 PeV is widely believed to have a Galactic origin, but the acceleration mechanism and identification of PeVatrons remain key open questions in high-energy astrophysics. Recent precise measurements by LHAASO reveal that the proton and helium spectra exhibit a common rigidity-dependent spectral break at ~ 3.5 PV, imposing a stringent constraint on source models. In this work, we construct, for the first time, a time-dependent cosmic-ray injection model that incorporates the full evolution of massive stars together with the dynamical development of wind termination shocks. We find that stellar winds of individual massive stars cannot explain the common spectral break observed by LHAASO, as they yield distinct rigidity cutoffs for protons and helium. By contrast, collective winds of massive star clusters naturally reconcile this discrepancy through the mixing effect of stars at different evolutionary stages. We propose a stellar-dominated model in which supernova remnants dominate the GeV-TeV range, individual stellar winds dominate the TeV range, and collective cluster winds dominate the PeV knee region. This model successfully reproduces the rigidity-dependent spectral features of various species near 100 GV and 0.1 PV. It further makes two testable predictions for future observations. Around 0.5 PV, the energy spectra of carbon and oxygen are expected to exhibit hardening similar to that of helium, which can be verified by LHAASO observations. In the multi-TV range, the energy spectrum of magnesium is not expected to show hardening similar to that observed for helium, carbon, and oxygen, which can be tested by DAMPE observations.

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arXiv2026

Radio Study of G76.9+1.0 Pulsar Wind Nebula

Pulsar Wind Nebulae (PWNe) are key astrophysical laboratories for high energy phenomena. Specifically, radio observations and related polarimetry are essential probes to understand acceleration and transport, as well as PWN interaction with environment. We aim to better study the multi-wavelength morphology and magnetic geometry of \gname\ PWN (a system between early and middle ages). We conduct high resolution VLA observations at 3 cm (X band), 6 cm (C band), and 13 cm (S band) and compare them with the archival Chandra X-ray data. We also performed spectral analysis and radio polarimetry based on our radio observations. Our new VLA observations reveal a north-south double-lobed PWN bracketing a bridge-like feature, with the pulsar clearly resolved at C and S bands. The polarization fraction reaches 30\% across all bands, with the bridge region showing ordered north-south magnetic fields aligned with the X-ray torus elongation, while the southern outer lobe exhibits fields not following such a direction and the northern lobe displays a more chaotic configuration. Notably, we detect a significant radio-X-ray anti-correlation near the pulsar, with bright radio emission appearing just beyond the compact X-ray PWN boundary, multiwavelength spectral analysis suggest distinct particle populations. The radio PWN spectral index steepens from $\alpha\sim-0.3$ in the inner bridge to $<-1.0$ in the outer lobes, yet we suggest it is less likely related to synchrotron cooling. We tried to use a thick torus model with toroidal $B$-field to reproduce observed features; the result implies possible particle deceleration in the radio PWN. The equipartition magnetic field strength is estimated to be $\sim$15.3\,$\mu$G.

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arXiv2026

Deciphering the IceCube Diffuse Neutrino Observations via AGN Variability

The physical origin of the diffuse neutrino background and its spectral break at $\sim$ 30 TeV remain a major puzzle in multi-messenger astrophysics. In this work, we demonstrate that this spectral feature is a natural consequence of AGN activity cycles and the resulting cosmic ray (CR) propagation. We present a unified model coupling the active and quiescent phases of AGNs, where CRs accelerated in the active core undergo subsequent diffusion and hadronic interactions in the host galaxy during the quiescent phase. The superposition of these distinct evolutionary phases yields dual spectral breaks, particularly the one at tens of TeV. Under realistic energetics, our model simultaneously accounts for the IceCube diffuse flux and fits the neutrino emissions of diverse sources, ranging from the blazar TXS 0506+056 to the Seyfert galaxies NGC 7469, CGCG 420-015, and the Circinus Galaxy. Our findings reveal that temporal variability is essential for deciphering the cosmic neutrino landscape and tracking high-energy CR escape.

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arXiv2026

Catching TeV emission from GRB 221009A and alike with LHAASO, LACT and SWGO

Gamma-Ray Bursts (GRBs) are the most energetic electromagnetic explosions in the universe. Recently, the Large High Altitude Air Shower Observatory (LHAASO) reported the breakthrough observation of GRB 221009A with gamma-ray energies beyond 13 TeV. This discovery, together with the previous GRB detection well above 100 GeV, confirms the production of very-high-energy (VHE, $\gtrsim 100$ GeV) radiation which might be a common component of all bright GRBs. It is reasonable to expect that bright GRBs are important targets for ground-based gamma-ray experiments. In this work, we estimate the detection rate for current and upcoming ground-based gamma-ray observatories including LHAASO, Large Array of Imaging Atmospheric Cherenkov Telescopes (LACT) and the Southern Wide-field Gamma-ray Observatory (SWGO) under two emission models with GRB~221009A as the template: first, that they all share the same intrinsic VHE spectral shape; second, they have the same environmental parameter and electron spectral index, governing their synchrotron self-Compton (SSC) emission. Using the long GRB luminosity and redshift distribution function obtained from the Fermi-GBM GRB samples, and accounting for the cosmological effects and extra-galactic background light (EBL) absorption, we derive the expected VHE flux at Earth. The sensitivity analysis for LHAASO, the upcoming LACT, and SWGO to evaluate their detection potential across specific redshift and luminosity ranges has been performed. The corresponding 5$\sigma$ detection rates of 221009A-like GRBs for the two emission models are: LHAASO, 0.04-0.05 yr$^{-1}$; LACT, 0.03-0.06 yr$^{-1}$; SWGO, 0.2-0.4 yr$^{-1}$. These rates can vary by up to $\approx 24\%$ due to different EBL models.

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arXiv2026

Radio Study of Vela X Cocoon

The evolution of pulsar Wind Nebulae (PWNe) influences how high energy particles in the vicinity are generated and transport. The Vela PWN (only $\sim300$\,pc away), provides a rather rare case between young and well-evolved systems. We therefore performed new 6 and 16\,cm high-resolution observations of the Vela X Cocoon region with the Australia Telescope Compact Array (ATCA). The observations reveal a complex region with a $\sim0.5^\circ$ major curved filament extending to far south from the pulsar, as well as other intersecting filaments and wisps. Our spectral analysis hints its connection with the PWN. Our results also found strongly linearly polarized emission, ordered and tangential $B$-field to the filaments. We find the rotation measure (RM) and polarization fraction (PF) along the filament are anti-correlated with the total intensity. We develop a simple 3D model of a spiral filament to explain these, while the PF distribution requires external interpretations such as interaction with the reverse shock. Comparison with archival data suggests that large scale features like the major filament are generally stable and large motions near the X-ray filament, all these confirm the distinction between radio and X-ray features.

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arXiv2024

A proposed deep sea Neutrino Observatory in the Nanhai

Over the past ten years, several breakthroughs have been made in multi-messenger astronomy. Thanks to the IceCube Neutrino Observatory, the detection of astrophysical neutrinos was proved to be practical. However, due to the limited statistics and field of view, only a few sources have been associated with IceCube neutrinos, making new and larger neutrino telescopes necessary. We propose the NEutrino Observatory in the Nanhai (NEON), located in the South China Sea to be complementary for the global neutrino detectors. This proposal describes the design and layout of the array and reports on comprehensive simulations conducted to assess its performance. The NEON project, with a volume of 10 km$^3$, achieves an angular resolution of 0.1$^\circ$ at 100 TeV. With 10 years of operation, the project's 5$\sigma$ sensitivity is estimated as $E^2\Phi \sim 2 \times 10^{-10}$ GeV cm$^{-2}$ s$^{-1}$ for a source spectrum index of -2. We found that the variation in depth from 1700 to 3500 meters does not significantly influence the sensitivity to steady sources.

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arXiv2023

Multi-messenger Study of Galactic Diffuse Emission with LHAASO and IceCube Observations

With the breakthrough in PeV gamma-ray astronomy brought by the LHAASO experiment, the high-energy sky is getting richer than before. Lately, LHAASO Collaboration reported the observation of a gamma-ray diffuse emission with energy up to the PeV level from both the inner and outer Galactic plane. In these spectra, there is one bump that is hard to explain by the conventional cosmic-ray transport scenarios. Therefore, we introduce two extra components corresponding to unresolved sources with exponential-cutoff-power-law (ECPL) spectral shape, one with an index of 2.4, and 20 TeV cutoff energy, and another with index of 2.3 and 2 PeV cutoff energy. With our constructed model, we simulate the Galactic diffuse neutrino flux and find our results are in full agreement with the latest IceCube Galactic plane search. We estimate the Galactic neutrino contributes of $\sim 9\%$ of astrophysical neutrinos at 20 TeV. In the high-energy regime, as expected most of the neutrinos observed by IceCube should be from extragalactic environments.

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arXiv2023

A New Scenario of Solar Modulation Model during the Polarity Reversing

When the Galactic Cosmic Rays (GCRs) entering the heliosphere, they encounter the solar wind plasma, and their intensity is reduced, so-called solar modulation. The modulation is caused by the combination of a few factors, such as particle energies, solar activity and solar disturbance. In this work, a 2D numerical method is adopted to simulate the propagation of GCRs in the heliosphere with SOLARPROP, and to overcome the time-consuming issue, the machine learning technique is also applied. With the obtained proton local interstellar spectra (LIS) based on the observation from Voyager 1 and AMS-02, the solar modulation parameters during the solar maximum activity of cycle 24 have been found. It shows the normalization and index of the diffusion coefficient indeed reach a maximal value in February 2014. However, after taking into account the travel time of particles with different energies, the peak time was found postponed to November 2014 as expected. The nine-month late is so-called time lag.

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arXiv2020

Solar modulation of cosmic proton and helium with AMS-02

We investigate the solar modulation effect with the long time cosmic ray proton and helium spectrum measured by AMS-02 on the time scale of a Bartels rotation (27 days) between May 2011 and May 2017. The time-span covers the negative heliospheric magnetic field polarity cycle, the polarity reversal period and the positive polarity cycle. The unprecedented accuracy of AMS-02 observation data provide a good opportunity to improve the understanding of the time dependent solar modulation effect. In this work, a two-dimensional solar modulation model is used to compute the propagation of cosmic rays in the heliosphere. Some important ingredients of the model which reflect the global heliospherical environment are taken from the observations. The propagation equation is numerically solved with the pubic Solarprop code. We find that the drift effect is suppressed during the high solar activity period but nearly recovered in the first half of 2017. The time-dependent rigidity dependence of the mean free path is critical to reproduce the observations between August 2012 and October 2015.

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