arXiv subjects

Hou-Dun Zeng

Publications and source records attributed to Hou-Dun Zeng.

7 recordsLinked to original sources

arXiv2026

Time-dependent Evolution of Proton Spectra in Supernova Remnants and Their Contribution to Galactic Cosmic Rays

Recent $\gamma$-ray observations indicate that the proton spectra of supernova remnants (SNRs) are well described by broken power laws, with both the spectral break energy, $E_{\mathrm{br}}$, and the low-energy spectral index, $\alpha$, exhibiting systematic evolution with SNR age. The physical origin of these evolutionary trends and their implications for the Galactic cosmic-ray (CR) population remain poorly understood. In this work, we develop the temporal evolution model for protons in SNRs by extending the semi-analytical framework of Zhang \& Fang, in which both the maximum acceleration energy and the injection spectral index evolve with the dynamical evolution of the remnant. The calculated proton spectra reproduce the age-dependent trends of both $E_{\mathrm{br}}$ and $\alpha$ inferred from observations. We adopt the proton spectrum at the onset of the radiative phase as the source spectrum for Galactic CR propagation and incorporate the intrinsic dispersion of source spectral indices among SNRs. The resulting cumulative Galactic proton spectrum is then calculated within a diffusion model. The propagated spectrum agrees well with the observed CR proton flux over a broad energy range, particularly above several tens of GeV. Our results provide a self-consistent framework linking the time-dependent evolution of proton acceleration in individual SNRs to the Galactic CR proton spectrum observed at Earth, and further support the long-standing hypothesis that SNRs are the dominant sources of Galactic CR protons below the knee.

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arXiv2025

Constraining the Luminosity Function and Delay-Time Distribution of Short Gamma-Ray Bursts for Multimessenger Gravitational-Wave Detection Rate Estimation

In this work, we analyze the most recent short gamma-ray burst (sGRB) sample detected by the \emph{Fermi} satellite to reassess the sGRB luminosity function and formation rate. Using the empirical redshift-luminosity correlation, we first determine the pseudo redshifts of 478 sGRBs. Then, we use the maximum likelihood method to constrain the luminosity function and formation rate of sGRBs under various delay-time distribution models, finding the Gaussian delay model statistically preferred over the power-law and lognormal delay models based on the Deviance Information Criterion. The local formation rate of sGRBs is $R_{\mathrm{sGRB}}(0)=1.37_{-0.27}^{+0.30}$ $\mathrm{Gpc^{-3}\,yr^{-1}}$, largely independent of the adopted delay-time distribution model. Additionally, we investigate the potential for joint detection of sGRBs and their gravitational wave (GW) counterparts from binary neutron star mergers using both current and future GRB and GW facilities. For sGRB detection, we consider three existing satellites: \emph{Fermi}, the Space-based multi-band astronomical Variable Objects Monitor (\emph{SVOM}), and the Einstein Probe (\emph{EP}). For GW detection, we examine two International GW Networks (IGWN): a four-detector network consisting of LIGO Hanford, Livingston, Virgo, and KAGRA (IGWN4) and an upcoming five-detector network that includes these four detectors plus LIGO India (IGWN5). Incorporating the angular dependence of sGRB jet emission energy, our results show that for different delay-time distribution models, the joint sGRB and GW detection rates for \emph{Fermi}, \emph{SVOM}, and \emph{EP} with IGWN4 (IGWN5) lie within 0.19--0.27 $\mathrm{yr^{-1}}$ (0.93--1.35 $\mathrm{yr^{-1}}$), 0.07--0.10 $\mathrm{yr^{-1}}$ (0.51--0.79 $\mathrm{yr^{-1}}$), and 0.01--0.03 $\mathrm{yr^{-1}}$ (0.15--0.27 $\mathrm{yr^{-1}}$), respectively.

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arXiv2024

Evolution of High-energy Electron Distribution in Pulsar Wind Nebulae

In this paper, we analyze the spectral energy distributions (SEDs) of 17 powerful (with a spin-down luminosity greater than $10^{35}$ erg s$^{-1}$) young (with an age less than 15000 yrs) pulsar wind nebulae (PWNe) using a simple time-independent one-zone emission model. Our aim is to investigate correlations between model parameters and the ages of the corresponding PWNe, thereby revealing the evolution of high-energy electron distributions within PWNe. Our findings are as follows: (1) The electron distributions in PWNe can be characterized by a double power-law with a superexponential cutoff; (2) As PWNe evolve, the high-energy end of the electron distribution spectrum becomes harder with the index decreasing from approximately 3.5 to 2.5, while the low-energy end spectrum index remains constant near 1.5; (3) There is no apparent correlation between the break energy or cutoff energy and the age of PWNe. (4) The average magnetic field within PWNe decreases with age, leading to a positive correlation between the energy loss timescale of electrons at the break energy or the high-energy cutoff, and the age of the PWN. (5) The total electron energy within PWNe remains constant near $2 \times 10^{48}$ erg, while the total magnetic energy decreases with age.

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arXiv2022

The Stellar-mass Function of Long Gamma-Ray Burst Host Galaxies

Long gamma-ray bursts (GRBs) have been discussed as a potential tool to probe the cosmic star formation rate (SFR) for a long time. Some studies found an enhancement in the GRB rate relative to the galaxy-inferred SFR at high redshifts, which indicates that GRBs may not be good tracers of star formation. However, in these studies, the GRB rate measured at any redshift is an average over all galaxies at that epoch. A deep understanding of the connection between GRB production and environment also needs to characterize the population of GRB host galaxies directly. Based on a complete sample of GRB hosts, we constrain the stellar-mass function (SMF) of GRB hosts, and examine redshift evolution in the GRB host population. Our results confirm that a strong redshift evolution in energy (with an evolution index of $δ=2.47^{+0.73}_{-0.89}$) or in density ($δ=1.82^{+0.22}_{-0.59}$) is needed in order to account for the observations. The GRB host SMF can be well described by the Schechter function with a power-law index $ξ\approx-1.10$ and a break mass $M_{b,0}\approx4.9\times10^{10}$ ${\rm M}_\odot$, independent of the assumed evolutionary effects. This is the first formulation of the GRB host SMF. The observed discrepancy between the GRB rate and the galaxy-inferred SFR may also be explained by an evolving SMF.

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arXiv2021

Effect of axion-like particles on the spectrum of the extragalactic gamma-ray background

Axion-like particles (ALPs) provide a feasible explanation for the observed lower TeV opacity of the Universe. If the anomaly TeV transparency is caused by ALPs, then the fluxes of distant extragalactic sources will be enhanced at photon energies beyond TeV, resulting in an enhancement of the observed extragalactic gamma-ray background (EGB) spectrum. In this work, we have investigated the ALP modulation on the EGB spectrum at TeV energies. Our results show that in the most optimistic case, the existence of ALPs can cause the EGB spectrum to greatly deviate from the prediction of a pure extragalactic-background-light (EBL) absorption scenario. The deviation occurs at approximately $\gtrsim$1 TeV, and the current EGB measurements by Fermi-LAT cannot identify such an effect. We also find that most of the sensitive ALP parameters have been ruled out by existing constraints, leaving only a small region of unrestricted parameters that can be probed using the EGB effect investigated in this work. Observations from forthcoming very-high-energy instruments like LHAASO and CTA may be beneficial for the study of this effect.

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arXiv2021

Revisiting the luminosity and redshift distributions of long gamma-ray bursts

In this work, we update and enlarge the long gamma-ray burst (GRB) sample detected by the {\it Swift} satellite. Given the incomplete sampling of the faint bursts and the low completeness in redshift measurement, we carefully select a subsample of bright {\it Swift} bursts to revisit the GRB luminosity function (LF) and redshift distribution by taking into account the probability of redshift measurement. Here we also explore two general expressions for the GRB LF, i.e., a broken power-law LF and a triple power-law LF. Our results suggest that a strong redshift evolution in luminosity (with an evolution index of $δ=1.92^{+0.25}_{-0.37}$) or in density ($δ=1.26^{+0.33}_{-0.34}$) is required in order to well account for the observations, independent of the assumed expression of the GRB LF. However, in a one-on-one comparison using the Akaike information criterion, the best-fitting evolution model involving the triple power-law LF is statistically preferred over the best-fitting one involving the broken power-law LF with a relative probability of $\sim94.3$\% versus $\sim5.7$\%. Extrapolating our fitting results to the flux limit of the whole {\it Swift} sample, and considering the trigger probability of {\it Swift}/Burst Alert Telescope in detail, we find that the expectations from our evolution models provide a good representation of the observed distributions of the whole sample without the need for any adjustment of the model free parameters. This further confirms the reliability of our analysis results.

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arXiv2019

The Luminosity Function and Formation Rate of A Complete Sample of Long Gamma-Ray Bursts

We study the luminosity function and formation rate of long gamma-ray bursts (GRBs) by using a maximum likelihood method. This is the first time this method is applied to a well-defined sample of GRBs that is complete in redshift. The sample is composed of 99 bursts detected by the $Swift$ satellite, 81 of them with measured redshift and luminosity for a completeness level of $82\%$. We confirm that a strong redshift evolution in luminosity (with an evolution index of $δ=2.22^{+0.32}_{-0.31}$) or in density ($δ=1.92^{+0.20}_{-0.21}$) is needed in order to reproduce the observations well. But since the predicted redshift and luminosity distributions in the two scenarios are very similar, it is difficult to distinguish between these two kinds of evolutions only on the basis of the current sample. Furthermore, we also consider an empirical density case in which the GRB rate density is directly described as a broken power-law function and the luminosity function is taken to be non-evolving. In this case, we find that the GRB formation rate rises like $(1+z)^{3.85^{+0.48}_{-0.45}}$ for $z\leq2$ and is proportional to $(1+z)^{-1.07^{+0.98}_{-1.12}}$ for $z\geq2$. The local GRB rate is $1.49^{+0.63}_{-0.64}$ Gpc$^{-3}$ yr$^{-1}$. The GRB rate may be consistent with the cosmic star formation rate (SFR) at $z\leq2$, but shows an enhancement compared to the SFR at $z\geq2$.

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