arXiv subjects

Xiaogu Zhong

Publications and source records attributed to Xiaogu Zhong.

6 recordsLinked to original sources

arXiv2026

Multi-Period Fermi-LAT and LHAASO Constraints on Axion-Like Particles from Mrk 421 via $χ^2$ Profile Likelihood with Gaussian Copula Correlation

We present a joint multi-period analysis of axion-like particles (ALPs) using five sets of simultaneous Fermi-LAT and LHAASO observations of the TeV blazar Mrk~421. Photon-ALP oscillations are calculated self-consistently together with EBL absorption for two representative jet emission models: a two-zone hybrid model and a single-zone hadronic model. To account for weak correlations among different observational epochs, we adopt a $χ^2$-based profile analysis combined with a Gaussian copula ($ρ=0.03$). Nuisance parameters are optimized under the no-ALP hypothesis before profiling the ALP parameters $m_a$ and $g_{aγ}$. In the low-mass regime ($m_a\lesssim1$\,neV) we obtain a 95\% CL upper limit of $g_{aγ}=6.35\times10^{-13}\,\mathrm{GeV}^{-1}$. Over the full mass range $0.1$--$500$\,neV, the most conservative 95\% CL upper limits are $g_{aγ}<6.69\times10^{-12}\,\mathrm{GeV}^{-1}$ (two-zone) and $g_{aγ}<7.37\times10^{-12}\,\mathrm{GeV}^{-1}$ (single-zone). Variations of the EBL template, the Galactic and intergalactic magnetic-field models, the spectral binning, and residual instrumental systematics change these limits by only a few percent. The jet magnetic field is the leading systematic and can shift the low-mass bound by a factor of a few; only a substantially weaker single-zone field degrades the constraint by about an order of magnitude. The analysis framework developed here provides a statistically consistent approach for future ALP searches with multi-messenger gamma-ray data.

astro-ph.HE↗

arXiv2026

Characterizing the origins of gamma-ray variability of the jetted active galactic nuclei observed with the Fermi-LAT

We conducted an analysis of gamma-ray variability in a large sample of jetted active galactic nuclei (AGNs) by utilizing archival Fermi-LAT light curves and applying damped random walk modeling to obtain variability amplitude. Our primary findings are summarized as follows: (1) The mean variability damping timescales of our sources are approximately 100 days. This damping timescale may imply that the diffusive shock acceleration plays an important role in the variability of gamma-ray emission. (2) Flat-spectrum radio quasars (FSRQs) demonstrate greater variability amplitude compared to BL Lacertae objects (BL Lacs). (3) The ratio of the distance of the emission region from the central supermassive black hole to the dusty torus radius for our sources is $R\approx2-4.5R_{\rm DT}$. In contrast, the ratio of the distance of the emission region from the central supermassive black hole to the BLR radius for our sources is $R\approx135-295R_{\rm BLR-in}$ and $R\approx123-270R_{\rm BLR-out}$. These findings indicate that the $γ$-ray emission region in jetted AGNs is likely located beyond the BLR, potentially could be associated with the dusty torus. (4) A statistical correlation is observed between variability amplitude and radio luminosity, radio loudness, X-ray luminosity, X-ray loudness, gamma-ray luminosity, and gamma-ray loudness, indicating a potential relationship between gamma-ray variability and jet activity. (5) Variability amplitude also shows a statistical correlations with synchrotron peak frequency luminosity, inverse Compton peak frequency luminosity, and Compton dominance. (6) Variability amplitude also correlates with black hole mass, accretion disk luminosity, and Eddington ratio, implying that the accretion disk may also contribute to gamma-ray variability.

astro-ph.HE↗

arXiv2026

A universal relationship between the variability timescale and black hole mass in black hole jetted and non-jetted accreting systems

A long-term variability study spanning a range of black hole mass systems, from microquasars hosting stellar-mass black holes to active galactic nuclei (AGNs) harboring supermassive black holes, provides new insights into the physics of relativistic jets. In this work, we investigate the optical variability of both jetted and nonjetted AGNs. We apply a stochastic process known as the Damped Random Walk (DRW) to model light curves from the Zwicky Transient Facility (ZTF) DR23. Our results show that the mass-scaled characteristic timescales across the black hole mass exhibit a linear relationship with a slope of 0.35-0.50. This analysis confirms a previously observed correlation between the damping timescales and black hole mass and extends it by incorporating 125 newly identified non-jetted AGNs selected from the Burst Alert Telescope (BAT) AGN catalogue. The derived slope of the relation between the damping timescales and black hole mass aligns with recent theoretical predictions, supporting the presence of a universal accretion mechanism in AGNs across different mass scales. Furthermore, our findings suggest a novel implication: the properties and production mechanisms of relativistic jets may be largely independent of black hole mass.

astro-ph.HE↗

arXiv2026

CosmicWeb-21cm array: A New Radio Observation Array Design for 21cm Cosmology

This paper presents the CosmicWeb-21cm array, a novel radio interferometer designed to overcome the key challenges in 21 cm cosmology. Its core innovations include: (1) a multi-scale nested geometry combining a hexagonal core with logarithmic spiral arms for excellent UV coverage and calibration robustness; (2) an intelligent non-uniform frequency sampling strategy that adapts resolution to foreground and signal characteristics, reducing data volume while preserving information; and (3) a machine-learning-enhanced, physics-informed processing pipeline that achieves 99.7\% foreground removal efficiency; (4) a dual-polarization crossed dipole integrated with a dielectric lens and cryogenically cooled LNA, achieving stable beam patterns and low noise temperature ($<35$ K) across 50-250 MHz. These co-designed advances enable high sensitivity mapping of the Epoch of Reionization, dark energy constraints and cosmic-web structure.

astro-ph.IM↗

arXiv2023

General Physical Properties of Fermi blazars

We study the general physical properties of Fermi blazars using the Fermi fourth source catalog data (4FGL-DR2). The quasi-simultaneous multiwavelength data of Fermi blazar are fitted by using the one-zone leptonic model to obtain some physical parameters, such as jet power, magnetic field and Doppler factor. We study the distributions of the derived physical parameter as a function of black hole mass and accretion disk luminosity. The main results are as follows. (1) For a standard thin accretion disk, the jet kinetic power of most FSRQs can be explained by the BP mechanism. However, the jet kinetic power of most BL Lacs can not be explained by both the BZ mechanism or the BP mechanism. The BL Lacs may have ADAFs surrounding their massive black holes. (2) After excluding the redshift, there is a moderately strong correlation between the jet kinetic power and jet radiation power and the accretion disk luminosity for Fermi blazars. These results confirm a close connection between jet and accretion. The jet kinetic power is slightly larger than the accretion disk luminosity for Fermi blazars. (3) There is a significant correlation between jet kinetic power and gamma-ray luminosity and radio luminosity for Fermi blazars, which suggests that gamma-ray luminosity and radio luminosity can be used to indicate the jet kinetic power.

astro-ph.HE↗

arXiv2013

A magnetic reconnection origin for the soft X-ray excess in AGN

We present a new scenario to explain the soft X-ray excess in Active Galactic Nucleus. The magnetic reconnection could happen in a thin layer on the surface of accretion disk. Electrons are accelerated by shock wave and turbulence triggered by magnetic reconnection, then they take place inverse Compton scattering above accretion disk which contributes soft X-rays. Based on standard disk model, we estimate the magnetic field strength and the energy released by magnetic reconnection along accretion disk, and find that the luminosity caused by magnetic reconnection mainly emits in the inner disk which is dominated by radiation pressure. We then apply the model to fit the spectra of AGNs with strong soft X-ray excess.

astro-ph.HE↗