arXiv subjects

Zejun Jiang

Publications and source records attributed to Zejun Jiang.

9 recordsLinked to original sources

arXiv2026

To understand the radiative processes of pulsars and fast radio bursts with the FAST

The radiative mechanism of coherent radio emission has remained an enigma since the discovery of pulsars, even the emergence of fast radio bursts (FRBs), which exhibit similarities to the single-pulse behavior of pulsars and have opened a new view for deciphering the long-standing mystery. Besides tremendous efforts in modelling, advanced facilities matter for solving the problem. The authors review the observational breakthroughs from the Five-hundred-meter Aperture Spherical radio Telescope (FAST), which are providing pivotal insights to unravel the underlying physics of pulsars and FRBs. This study offers a novel perspective in the era when pulsars meet FRBs, and further investigations are encouraged to utilize the highly sensitive telescope, the FAST.

astro-ph.HE↗

arXiv2023

Implications of a Possible Spectral Structure of Cosmic-ray Protons Unveiled by the DAMPE

The recent observations revealed that the cosmic-ray (CR) proton spectrum showed a complex structure: the hardening at $\rm \sim 200~GeV$ and softening at $\rm \sim 10~TeV$. However, so far the physical origins of this spectral feature remain strongly debated. In this work, we simulate the acceleration of cosmic-ray protons in a nearby Supernova remnant (SNR) by solving numerically the hydrodynamic equations and the equation for the quasi-isotropic CR momentum distribution in the spherically symmetrical case to derive the spectrum of protons injected into the interstellar medium (ISM), and then simulate the propagation process of those accelerated CR particles to calculate the proton fluxes reaching the Earth. Besides, we use the DRAGON numerical code to calculate the large-scale cosmic-ray proton spectrum. Our simulated results are in good agreement with the observed data (including the observed data of proton fluxes and dipole anisotropy). We conclude that the spectral feature of cosmic-ray protons in this energy band may originate from the superposition of the distribution from the nearby SNR and background diffusive cosmic-ray component. We find that the release of particles from this nearby SNR has a time delay. Besides, it can be found that the nonlinear response of energetic particles, release time of CR protons, and age of the local SNR can leave strong signatures in the spectrum of the resulting CR proton fluxes.

astro-ph.HE↗

arXiv2022

Dynamically Retrieving Knowledge via Query Generation for Informative Dialogue Generation

Knowledge-driven dialog system has recently made remarkable breakthroughs. Compared with general dialog systems, superior knowledge-driven dialog systems can generate more informative and knowledgeable responses with pre-provided knowledge. However, in practical applications, the dialog system cannot be provided with corresponding knowledge in advance because it cannot know in advance the development of the conversation. Therefore, in order to make the knowledge dialogue system more practical, it is vital to find a way to retrieve relevant knowledge based on the dialogue history. To solve this problem, we design a knowledge-driven dialog system named DRKQG (Dynamically Retrieving Knowledge via Query Generation for informative dialog response). Specifically, the system can be divided into two modules: the query generation module and the dialog generation module. First, a time-aware mechanism is utilized to capture context information, and a query can be generated for retrieving knowledge through search engine. Then, we integrate the copy mechanism and transformers, which allows the response generation module to produce responses derived from the context and retrieved knowledge. Experimental results at LIC2022, Language and Intelligence Technology Competition, show that our module outperforms the baseline model by a large margin on automatic evaluation metrics, while human evaluation by the Baidu Linguistics team shows that our system achieves impressive results in Factually Correct and Knowledgeable.

cs.CL↗

arXiv2022

Trajectories and Radiation of Charged Particles in the Pulsar Magnetosphere

Trajectories and radiation of the accelerating electrons are studied in the pulsar magnetosphere approximated as the electromagnetic field of the Deutsch's solutions. Because the electrons are accelerated rapidly to ultra-relativistic velocity near the neutron star surface, the electron velocity vector (and then its trajectory) is derived from the balance between Lorentz force and radiation reaction force, which makes the pitch angle between electron trajectories and magnetic field lines nonzero in most part of the magnetosphere. In such a case, the spectral energy distributions (SEDs) of synchro-curvature radiation for the accelerating electrons with a mono-energetic form are calculated. Our results indicate that: (i) the pitch angle is the function of electron position ($r, \theta, \phi$) in the open field line regions, and increases with increasing $r$ and $\theta$ as well as increasing the inclination angle; (ii) the radius of curvature becomes large along the particle trajectory, and (iii) the SED appears a double peak structure depending on the emission position, where the synchrotron radiation plays an important role in X-ray band and curvature radiation mainly works in GeV band, which is only determined by parameters $\alpha$ and $\zeta$

hep-ph↗

arXiv2022

Ultrahigh-energy Gamma-Ray Radiation from the Crab Pulsar Wind Nebula

It has been long debated whether the high-energy gamma-ray radiation from the Crab nebula stems from leptonic or hadronic processes. In this work, we investigate the multi-band non-thermal radiation from the Crab pulsar wind nebula with the leptonic and leptonic-hadronic hybrid models, respectively. Then we use the Markov Chain Monte Carlo(MCMC) sampling technology and method of sampling trace to study the stability and reasonability of the model parameters according to the recent observed results and obtain the best-fitting values of parameters. Finally, we calculate different radiative components generated by the electrons and protons in the Crab nebula. The modeling results indicate that the pure leptonic origin model with the one-zone only can partly agree with some segments of the data from various experiments (including the $\rm PeV$ gamma-ray emission reported by the LHAASO and the other radiation ranging from the radio to very high energy (VHE) gamma-ray waveband), and the contribution of hadronic interaction is hardly constrained. However, we find that the hadronic process may also contribute, especially in the energy range exceeding the $\rm PeV$. In addition, it can be inferred that the higher energy signals from the Crab nebula could be observed in the future.

astro-ph.HE↗

arXiv2021

Likely GeV emission from an old Supernova Remnant: SNR G206.9+2.3

A novel $\gamma$-ray supernova remnant (SNR) G206.9+2.3 is first reported in this study. We arrived at this conclusion after analyzing 12.4 years of observation data of the Fermi Large Area Telescope (Fermi-LAT). The photon flux of the remnant was (1.19$\pm$0.59) 10$^{-9}$ cm$^{-2}$ s$^{-1}$, and its power-law spectral index was 2.22$\pm$0.19 in the 0.2-500 GeV energy band. Moreover, we found that the test statistic values of the global fit from the four different energy bands were greater than 9. We identified that this was a real $\gamma$-ray signal. Furthermore, we found that its GeV spatial location was in good agreement with that of its radio band. Its spectral energy distribution and light curve properties were similar to those of SNRs. We suggest that the novel $\gamma$-ray source is a likely counterpart to SNR G206.9+2.3. Consequently, we discuss its likely leptonic or hadronic origin.

astro-ph.HE↗

arXiv2021

likely Detection of GeV gamma-Ray Emission from the composite supernova remnant COMP G327.1+1.1 with Fermi-LAT

We report the likely GeV $\gamma$-ray emission from the composite supernova remnant (SNR) COMP G327.1+1.1 by analyzing $\sim$12.2 years of the \textit{Fermi} Large Area Telescope (\textit{Fermi}-LAT) Pass 8 data. We found the features of its \textbf{ranges of} spectrum and luminosity are well consistent with those of the observed COMP SNRs in the Milky Way. Moreover, the position of the source matches those in radio and TeV energy bands, we propose that the $\gamma$-ray source is likely to be a GeV counterpart of COMP G327.1+1.1. Considering the case of the association from COMP G327.1+1.1 and the $\gamma$-ray source, we interpreted its broadband spectral energy distribution (SED) by using three simple stationary models including one-zone and two-zone leptonic models and one-zone leptohadronic model. We found that the simple two-zone model dominated by leptons can better explain its SED. More high-energy data are expected to firmly confirm the association between the $\gamma$-ray source and COMP G327.1+1.1 in the future.

astro-ph.HE↗

arXiv2021

Detection of GeV $\gamma$-Ray Emission from supernova remnant SNR G15.9+0.2 with Fermi-LAT

We first report GeV $\gamma$-ray emission from supernova remnant (SNR) G15.9+0.2 in this work. The results show that its power-law spectral index is 2.94$\pm$0.25 with a 6.47$\sigma$ significance level, and the $\gamma$-ray emission can be characterized by a two-dimensional (2D) Gaussian spatial distribution, which has a better improvement than the case of a point source. Moreover, we find that its likely counterparts from the radio, X-ray, and TeV energy bands are well coincident with its spatial location. We suggest that the new $\gamma$-ray emission may originate from SNR G15.9+0.2. Analyzing the variability from 12.4 years of the light curve (LC), we identify that this LC exists weak variability with a 2.69$\sigma$ variability significance level. We investigated the 2D Gaussian extended region and did not identify certified active galactic nuclei from the region of this SNR; thus, we suggest that the new $\gamma$-ray emission may originate from SNR G15.9+0.2. On this basis, we discussed the probable origins of its $\gamma$-ray radiation from leptonic and hadronic scenarios, respectively.

astro-ph.HE↗

arXiv2021

Fermi-LAT Detection of GeV Gamma-Ray Emission from The Highly Asymmetric Shell Supernova Remnant: SNR G317.3-0.2

In this paper, we report the first extended GeV $\gamma$-ray emission, at a significant level of $\sim$ 8.13$\sigma$, from the region of the supernova remnant (SNR) SNR G317.3-0.2 by analyzing $\sim$ 12.2 years of Fermi Large Area Telescope (Fermi-LAT) Pass 8 data in the work. The best-fit position of the new $\gamma$-ray source matches that of the 843 MHz radio energy band of SNR G317.3-0.2, and there is no significant variability of the photon flux of the corresponding light curve (LC) in the data for the 12.2 year period; therefore, by excluding other known $\gamma$-ray sources or candidates within a 2$\sigma$ error radius from the best-fit position of SNR G317.3-0.2, we suggest that the $\gamma$-ray source is likely to be a GeV counterpart of SNR G317.3-0.2.

astro-ph.HE↗