arXiv subjects

Qinyuan Zhang

Publications and source records attributed to Qinyuan Zhang.

4 recordsLinked to original sources

arXiv2025

Cosmogenic Neutrino Point Source and KM3-230213A

Cosmogenic neutrinos (CNs) are produced by ultra-high energy cosmic rays (UHECRs) interacting with cosmic background radiation. We investigated the properties of CN point/extended sources, i.e, the neutrino spectrum, and angular profile as functions of time, by assuming that UHECR sources are transient events, such as gamma-ray bursts. The properties depend much on the intergalactic magnetic field (IGMF), but the angular extent is in general sub-degree, within which the CN flux can overshoot the diffuse CN flux in early time. The nearby CN point sources could be detected for the low IGMF case by future neutrino telescopes. The recent KM3-230213A event is possible to account for by a nearby transient CN source, rather than diffuse CN emission. Observations of CN point sources will provide a chance to search for UHECR sources.

astro-ph.HE↗

arXiv2025

Observe Gamma-Rays and Neutrinos Associated with Ultra-High Energy Cosmic Rays

IceCube measures a diffuse neutrino flux comparable to the Waxman-Bahcall bound, which suggests the possibility that the ultra-high energy cosmic rays (UHECRs) have a common origin with diffuse high energy neutrinos. We propose high energy gamma-ray and/or neutrino observations toward the arrival directions of UHECRs to search for the sources and test this possibility. We calculate the detection probability of gamma-ray/neutrino sources, and find that the average probability per UHECR of >10 EeV is $\sim$10% if the sensitivity of the gamma-ray or neutrino telescope is $\sim$10$^{-12}$ erg cm$^{-2}$s$^{-1}$ and the source number density is $\sim$10$^{-5}$ Mpc$^{-3}$. Future gamma-ray and neutrino observations toward UHECRs, e.g., by LHAASO-WCDA, CTA, IceCube/Gen2, are encouraged to constrain the density of UHECR sources or even identify the sources of UHECRs.

astro-ph.HE↗

arXiv2025

Overall Ultra-high Energy Neutrino Emission from GRBs during Jet Expansion

The ultra-relativistic jet released in gamma-ray bursts (GRBs) is expected to produce ultra-high-energy cosmic rays (UHECRs), prompt gamma-ray emission and hence prompt high-energy neutrinos by photopion interactions. In this work, we calculate the time-integrated neutrino spectrum during the expansion of jets by taking into account the time evolution of cosmic ray and secondary spectra and neutrino production. We numerically solve the continuity equations for nucleons, pions, and muons for their spectral evolution. Since pion and muon damping weakens as the jet expands, the neutrino production at large radii at high energies may dominate that around the jet energy dissipation radius. Compared with the usually adopted approaches that only consider neutrino production around the energy dissipation radius, the overall UHE neutrino fluence integrated over time can be significantly larger, and the flavor fraction of electron neutrinos as function of neutrino energy is different at UHE, due to neutrino production at radii much larger than the energy dissipation radius. The faster magnetic field decay leads to larger UHE neutrino fluence, and the UHE neutrino spectra is weakly dependent on the energy dissipation radius and the jet Lorentz factor. Observations of prompt EeV neutrinos from GRBs by the next-generation neutrino telescopes, e.g., GRAND and IceCube-Gen2, will test the hypothesis of GRBs as UHECR sources and probe the physics of GRB jets.

astro-ph.HE↗

arXiv2024

Implication of Jet Physics from MeV Line Emission of GRB 221009A

Ultrarelativistic jets are believed to play an important role in producing prompt emission and afterglow of gamma-ray bursts (GRBs), but the nature of the jet is poorly known owing to the lack of decisive features observed in the prompt emission. The discovery of an emission line evolving from about 37 to 6 MeV in the brightest-of-all-time GRB 221009A provides an unprecedented opportunity to probe GRB jet physics. The time evolution of the central energy of the line with power-law index $-1$ is naturally explained by the high-latitude curvature effect. Under the assumption that the line emission is generated in the prompt emission by $e^\pm$ pair production, cooling, and annihilation in the jet, we can strictly constrain jet physics with observed line emission properties. We find that the radius of the emission region is $r\gtrsim10^{16}$ cm. The narrow line width of $\sim10\%$ requires that the line emission occurs within $\sim10\%$ of the dynamical time, which further implies short timescales of pair cooling to the nonrelativistic state and pair annihilation, as well as a slightly clumpy emission region. If the jet's Lorentz factor is $Γ\gtrsim400$, the fast cooling requirement needs an energy density of magnetic field in the jet much larger than that of prompt gamma rays, i.e., a magnetically dominated jet. The temporal behavior of line flux suggests some angle dependence of line emission. We also discuss the difficulties of other scenarios for the observed emission line.

astro-ph.HE↗