arXiv subjects

Yunchuan Xiang

Publications and source records attributed to Yunchuan Xiang.

8 recordsLinked to original sources

arXiv2026

Spin precession in the strong deflection limit

The strong deflection limit (SDL) of the deflection angle is well established for general spherically symmetric spacetimes, but a systematic SDL treatment of spin precession has been lacking. We derive the SDL expansion for the spin precession angle of particles propagating along geodesics in static, spherically symmetric, and asymptotically flat spacetimes. The SDL coefficients are obtained, and a simple relation linking the precession angle to the deflection one is established. Applying the formalism to Schwarzschild and Reissner-Nordstr\"om (RN) spacetimes, we obtain fully analytic SDL coefficients for the former and perturbative charge corrections to $\mathcal{O}(Q^2)$ for the latter. These results explicitly verify the universal spin-flip of massless particles in backward scattering, which is the underlying mechanism governing the absence of the glory spot. While the spin precession of massless particles is charge-independent, massive particles acquire a non-trivial charge dependence that distinguishes the RN case from Schwarzschild.

gr-qc↗

arXiv2026

A Novel Pipeline for the Identification of New Gamma-Ray Blazars from the 4FGL-Xiang-DR2 Catalog Based on Multi-wavelength Flux Distributions

The identification and classification of Fermi blazars are core topics in high-energy astrophysics. To enable precise spatial cross-identification, we constructed two high-precision catalogs: the updated 4FGL-Xiang-DR2 (DR2) and a supplementary version of the fifth edition of Roma-BZCAT (\texttt{5BZCAT\_err}). We then developed and applied a novel four-step analytical pipeline combining cross-matching with the statistical analysis of multi-band flux distributions to identify new Fermi blazars. The analytical pipeline has yielded several key results in the systematic comparison of BZBs and BZQs. We found that among single statistical metrics, kurtosis is the most powerful discriminator (MAD~$>$~1.64). At the overall distribution level, the 1.4~GHz, 843~MHz, 5~GHz, 0.1--2.4~keV, and 0.3--10~keV bands show significant divergence (JSD~$>$~0.3). Building on these findings, our proposed ``Box-Cox$+$TND'' model successfully fits the observed flux distributions between BZBs and BZQs. Applying this entire pipeline, we successfully identified 17 new blazars. The validity of these associations is strongly supported by our multi-wavelength flux model, which confirms that 15 of the 17 candidates are statistically consistent with the known blazar population, falling within the $2σ$ confidence interval. Although the two remaining sources exhibit some statistical deviation in the gamma-ray band, their strong consistency in other wavebands, coupled with high spatial association probabilities, leads us to conclude that their associations are also reliable and should not be readily excluded.

astro-ph.HE↗

arXiv2024

The precession of particle spin in spherical symmetric spacetimes

In this work, we will explore the precession of particle spins in spherical spacetimes. We first argue that the geometrical optics (WKB) approximation is insufficient, due to the absence of a glory spot in the backward scattering of massless particles, making an analysis of spin precession necessary. We then derive the precession equation assuming the spin is parallel transported, which is supported by the sub-leading order of the WKB approximation. The precession equation applies to both massless and massive particles. For particles moving at the speed of light, we show that spin is always reversed after backward scattering in any spherically symmetric spacetime, confirming the absence of a glory spot for massless particles. Finally, we solve the precession equation for Schwarzschild and Reissner-Nordstr\"om spacetimes and discuss the spin precession of massive particles, particularly in the non-relativistic limit. We find that, in Schwarzschild spacetime, the spin precession for particles moving with very small velocities compared to the speed of light depends only on the deflection angle, while in Reissner-Nordstr\"om spacetime, it also depends on the black hole charge, as revealed by the expansion derived from the strong lensing approximation.

gr-qc↗

arXiv2023

Fermi-LAT detection of A new starburst galaxy candidate: IRAS 13052-5711

A likely starburst galaxy (SBG), IRAS 13052-5711, which is the most distant SBG candidate discovered to date, was found by analyzing 14.4 years of data from the Fermi large-area telescope (Fermi-LAT). This SBG's significance level is approximately 6.55$σ$ in the 0.1-500 GeV band. Its spatial position is close to that of 4FGL J1308.9-5730, determined from the Fermi large telescope fourth-source Catalog (4FGL). Its power-law spectral index is approximately 2.1, and its light curve (LC) for 14.4 years has no significant variability. These characteristics are highly similar to those of SBGs found in the past. We calculate the SBG's star formation rate (SFR) to be 29.38 $\rm M_{\odot}\ yr^{-1}$, which is within the SFR range of SBGs found to date. Therefore, IRAS 13052-5711 is considered to be a likely SBG. In addition, its 0.1-500 GeV luminosity is (3.28 $\pm$ 0.67) $\times 10^{42}\ \rm erg\ s^{-1}$, which deviates from the empirical relationship of the $γ$-ray luminosity and the total infrared luminosity. We considered a hadronic model to explain the GeV spectrum of IRAS 13052-5711.

astro-ph.HE↗

arXiv2021

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

We first report GeV $γ$-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$0.25 with a 6.47$σ$ significance level, and the $γ$-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 $γ$-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$σ$ 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 $γ$-ray emission may originate from SNR G15.9+0.2. On this basis, we discussed the probable origins of its $γ$-ray radiation from leptonic and hadronic scenarios, respectively.

astro-ph.HE↗

arXiv2021

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

A novel $γ$-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 $γ$-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 $γ$-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 $γ$-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 $γ$-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 $γ$-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 $γ$-ray source and COMP G327.1+1.1 in the future.

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 $γ$-ray emission, at a significant level of $\sim$ 8.13$σ$, 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 $γ$-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 $γ$-ray sources or candidates within a 2$σ$ error radius from the best-fit position of SNR G317.3-0.2, we suggest that the $γ$-ray source is likely to be a GeV counterpart of SNR G317.3-0.2.

astro-ph.HE↗