arXiv subjects

Wen-Qiang Liang

Publications and source records attributed to Wen-Qiang Liang.

7 recordsLinked to original sources

arXiv2026

Revealing the Physical Driver of the Baldwin Effect: Gas Density in the Broad-Line Region

The Baldwin effect --- the inverse correlation between the equivalent width of emission lines and the continuum luminosity in active galactic nuclei (AGNs) --- has been known for nearly five decades, yet its physical origin remains poorly understood. Using a sample of 41,159 radio quasars constructed from the Sloan Digital Sky Survey and the Low-Frequency Array Two-metre Sky Survey, we investigate the origin and underlying physics of the Baldwin effect of MgII broad emission lines in both radio-quiet (RQ) and radio-loud (RL) quasars. We find that the slope $β$ of the Baldwin effect is positively correlated with the Eddington ratio $λ_{\rm Edd}$ in both populations, and RL quasars exhibit steeper $β$ than their RQ quasars at fixed $λ_{\rm Edd}$. Photoionization simulations reveal that the $β$ is primarily governed by the gas density in the broad-line region (BLR): lower gas densities yield steeper slopes. This density-driven mechanism naturally connects the Baldwin effect to the broader AGN evolutionary context. Specifically, higher $λ_{\rm Edd}$ drive stronger accretion disk winds, leading to denser BLRs and shallower $β$. Our findings indicate that BLR gas density serves as the primary physical driver underlying the "global" Baldwin effect, offering a physically grounded framework for interpreting AGN accretion states and their coupled evolution with host galaxies.

astro-ph.GA↗

arXiv2025

The infrared traced star formation rates of associated absorption lines quasars

Some optically selected quasars exhibit Mg II assoicated absorption lines (AALs), and its origin remains unclear. In this paper, we compile a sample of 1769 quasars, with or without Mg II AALs. Of which 1689 are Far-Infrared (FIR) detected quasars and the rest are not detected in FIR. For the FIR undetected quasars, we obtain stacks for both with and without Mg II AAL quasars. Then we estimate the star formation rates (SFRs) within quasar host galaxies based on their FIR luminosities derived from their FIR greybody components, and find that, although quasars with Mg II AALs have significantly redder median composite spectra than those without Mg II AALs, the SFR distributions of the two types of quasars are statistically indistinguishable. These results do not require an evolutionary link between the quasars with and without Mg II AALs, and would be reconciled if an orientation effect cannot be ignored among the quasars hosting different types of absorption lines.

astro-ph.GA↗

arXiv2024

Observational Evidence of Particles Acceleration by Relativistic Magnetic Reconnection in Gamma-ray Bursts

Gamma-ray bursts (GRBs) as the most energetic explosions in the modern universe have been studied over half a century, but the physics of the particle acceleration and radiation responsible for their observed spectral behaviors are still not well understood. Based on the comprehensive analysis of the pulse properties in both bright GRB~160625B and GRB~160509A, for the first time, we identify evidences of particle acceleration by relativistic magnetic reconnection from the evolutionary behavior of the two spectral breaks ($E_{\rm p}$ and $E_{\rm cut}$). Meanwhile, the adiabatic cooling process of the emitting particles in the magnetic reconnection regions produces a relation between the spectral index and the flux. We also discuss the physics behind spectral energy correlations. Finally, we argue that the identification of an anticorrelation between $E_{\rm cut}$ and $L_{\rm iso}$ may opens a new avenue for diagnostics of the physics of the particle acceleration and radiation in a variety of astrophysical sources.

astro-ph.HE↗

arXiv2024

Reconstruction of luminosity function from flux-limited samples

The properties of the progenitors of gamma-ray bursts (GRBs) and of their environment are encoded in their luminosity function and cosmic formation rate. They are usually recovered from a flux-limited sample based on Lynden-Bell's $c^{-}$ method. However, this method is based on the assumption that the luminosity is independent of the redshift. Observationally, if correlated, people use nonparametric $τ$ statistical method to remove this correlation through the transformation, $L^{\prime}=L/g(z)$, where $z$ is the burst redshift, and $g(z)=(1+z)^{k}$ parameterizes the underlying luminosity evolution. However, the application of this method to different observations could result in very different luminosity functions. By the means of Monte Carlo simulation, in this paper, we demonstrate that the origin of an observed correlation, measured by the $τ$ statistical method, is a complex combination of multiple factors when the underlying data are correlated. Thus, in this case, it is difficult to unbiasedly reconstruct the underlying population distribution from a truncated sample, unless the detailed information of the intrinsic correlation is accurately known in advance. In addition, we argue that an intrinsic correlation between luminosity function and formation rate is unlikely eliminated by a misconfigured transformation, and the $g(z)$, derived from a truncated sample with the $τ$ statistical method, does not necessarily represent its underlying luminosity evolution.

astro-ph.GA↗

arXiv2023

GRB 200829A: External Shock Origin of the Very Early Prompt Emission?

Long-duration GRB~200829A was detected by Fermi-GBM and Swift-BAT/XRT, and then rapidly observed by other ground-based telescopes. It has a weak $γ$-ray emission in the very early phase and followed by a bright spiky $γ$-ray emission pulse. The radiation spectrum of the very early emission is best fitted by a power-law function with index $\sim -1.7$. However, the bright spiky $γ$-ray pulse, especially the time around the peak, exhibits a distinct two-component radiation spectra, i.e., Band function combined with a blackbody radiation spectrum. We infer the photospheric properties and reveal a medium magnetization at photospheric position by adopting the initial size of the outflow as $r_0=10^9$~cm. It implies that Band component in this pulse may be formed during the dissipation of magnetic field. The power-law radiation spectra found in the very early prompt emission may imply the external-shock origination of this phase. Then, we perform Markov Chain Monte Carlo method fitting on the light-curves of this burst, where the jet corresponding to the $γ$-ray pulses at around $20$~s is used to refresh the external-shock. It is shown that the light-curves of very early phase and X-ray afterglow after $40$~s, involving the X-ray bump at around $100$~s, can be well modelled in the external-shock scenario. For the obtained initial outflow, we estimate the minimum magnetization factor of the jet based on the fact that the photospheric emission of this jet is missed in the very early phase.

astro-ph.HE↗

arXiv2022

Jets in a Gamma-Ray Burst During its Prompt Emission: Evolution of Lorentz Factor

Knowledge about the Lorentz factor and its evolution of relativistic jets in gamma-ray bursts (GRBs) is crucial to understand their physics. An exact value of bulk Lorentz factor can be estimated based on a high-energy spectral cutoff, which may appear in GRBs' prompt emission owing to the absorption of photon-photon pair production. In this work, we focus on the investigation of the bulk Lorentz factor evolution of jets in an individual burst. Based on \textsl{Fermi} observations, we search for the bursts with multiple $γ$-ray pulses characterized by a high-energy spectral cutoff, and nine GRBs are obtained. Together with the estimation of the pulse duration and radiation spectrum, the Lorentz factor of jets corresponding to different pulses in an individual GRB are estimated. It is shown that the Lorentz factor of jets in an individual GRB fluctuates within a certain range and without a general trend in these nine GRBs. In addition, the Lorentz factors of the jets in GRBs~130821A, 160509A and 160625B seem to increase with time. We also study the relations among $L_{\rm iso }$, $E_{\rm p,z}$, and $Γ$ for the pulses in our sample, which is found to be consistent with that found in previous works.

astro-ph.HE↗

arXiv2022

Spectral evolution responsible for the transition from positive lags to negative lags in Gamma-ray Bursts

It was well known that most of gamma-ray bursts (GRBs) are dominated by positive spectral lags, while a small fraction of GRBs show negative lags. However, Wei et al. firstly identified a well-defined transition from positive lags to negative lags in GRB 160625B, and then got robust limits on possible violation of Lorentz Invariance (LIV) based on the observation. Recently, such a transition has been found in three different emission episodes in \thisgrb by Gunapati et al., which provides us a great opportunity to investigate whether the transition results from LIV-induced observed spectral lags. Our analysis shows that the LIV model can not be compatible with the current observations, whereas, only the spectral evolution induced spectral lags could responsible for the transition. So, spectral evolution can also explain the positive to negative lag in GRB 190530A.

astro-ph.HE↗