arXiv subjects

Yong-Zhong Qian

Publications and source records attributed to Yong-Zhong Qian.

At least 37 records · Page 2Linked to original sources

arXiv2022

Comparison of simulated neutrino emission models with data on Supernova 1987A

We compare models of supernova (SN) neutrino emission with the Kamiokande II data on SN 1987A using the Bayesian approach. These models are taken from simulations and are representative of current 1D SN models. We find that models with a brief accretion phase of neutrino emission are the most favored. This result is not affected by varying the overall flux normalization or considering neutrino oscillations. We also check the compatibility of the best-fit models with the data.

astro-ph.HE↗

arXiv2021

Stationary solutions for fast flavor oscillations of a homogeneous dense neutrino gas

We present a method to find the stationary solutions for fast flavor oscillations of a homogeneous dense neutrino gas. These solutions correspond to collective rotation of all neutrino polarization vectors around a fixed axis in the flavor space on average, and are conveniently studied in the co-rotating frame. We show that these solutions can account for the numerical results of explicit evolution calculations, and that even with the simplest assumption of adiabatic evolution, they can provide the average survival probabilities to good approximation. We also discuss improvement of these solutions and their use as estimates of the effects of fast oscillations in astrophysical environments.

astro-ph.HE↗

arXiv2020

Nucleosynthesis of an $11.8\,M_\odot$ Supernova with 3D Simulation of the Inner Ejecta: Overall Yields and Implications for Short-Lived Radionuclides in the Early Solar System

Based on a 3D supernova simulation of an $11.8\,M_\odot$ progenitor model with initial solar composition, we study the nucleosynthesis using tracers covering the innermost $0.1\,M_\odot$ of the ejecta. These ejecta are mostly proton-rich and contribute significant amounts of $^{45}$Sc and $^{64}$Zn. The production of heavier isotopes is sensitive to the electron fraction and hence the neutrino emission from the proto-neutron star. The yields of these isotopes are rather uncertain due to the approximate neutrino transport used in the simulation. In order to obtain the total yields for the whole supernova, we combine the results from the tracers with those for the outer layers from a suitable 1D model. Using the yields of short-lived radionuclides (SLRs), we explore the possibility that an $11.8\,M_\odot$ supernova might have triggered the formation of the solar system and provided some of the SLRs measured in meteorites. In particular, we discuss two new scenarios that can account for at least the data on $^{41}$Ca, $^{53}$Mn, and $^{60}$Fe without exceeding those on the other SLRs.

astro-ph.HE↗

arXiv2020

Potential Impact of Fast Flavor Oscillations on Neutrino-driven Winds and Their Nucleosynthesis

The wind driven by the intense neutrino emission from a protoneutron star (PNS) is an important site for producing nuclei heavier than the Fe group. Because of certain features in the neutrino angular distributions, the so-called fast flavor oscillations may occur very close to the PNS surface, effectively resetting the neutrino luminosities and energy spectra that drive the wind. Using the unoscillated neutrino emission characteristics from two core-collapse supernova simulations representative of relevant progenitors at the lower and higher mass end, we study the potential effects of fast flavor oscillations on neutrino-driven winds and their nucleosynthesis. We find that such oscillations can increase the total mass loss by factors up to ~ 1.5-1.7 and lead to significantly more proton-rich conditions. The latter effect can greatly enhance the production of 64Zn and the so-called light p-nuclei 74Se, 78Kr, and 84Sr. Implications for abundances in metal-poor stars, Galactic chemical evolution in general, and isotopic anomalies in meteorites are discussed.

astro-ph.HE↗

arXiv2020

Constraining the Milky Way Mass Profile with Phase-Space Distribution of Satellite Galaxies

We estimate the Milky Way (MW) halo properties using satellite kinematic data including the latest measurements from Gaia DR2. With a simulation-based 6D phase-space distribution function (DF) of satellite kinematics, we can infer halo properties efficiently and without bias, and handle the selection function and measurement errors rigorously in the Bayesian framework. Applying our DF from the EAGLE simulation to 28 satellites, we obtain an MW halo mass of $M=1.23_{-0.18}^{+0.21}\times 10^{12} M_\odot$ and a concentration of $c=9.4_{ -2.1}^{ +2.8}$ with the prior based on the $M$-$c$ relation. The inferred mass profile is consistent with previous measurements but with better precision and reliability due to the improved methodology and data. Potential improvement is illustrated by combining satellite data and stellar rotation curves. Using our EAGLE DF and best-fit MW potential, we provide much more precise estimates of kinematics for those satellites with uncertain measurements. Compared to the EAGLE DF, which matches the observed satellite kinematics very well, the DF from the semi-analytical model based on the dark-matter-only simulation Millennium II (SAM-MII) over-represents satellites with small radii and velocities. We attribute this difference to less disruption of satellites with small pericenter distances in the SAM-MII simulation. By varying the disruption rate of such satellites in this simulation, we estimate a $\sim 5\%$ scatter in the inferred MW halo mass among hydrodynamics-based simulations.

astro-ph.GA↗

arXiv2020

Neutrino signal from proto-neutron star evolution: Effects of opacities from charged-current-neutrino interactions and inverse neutron decay

We investigate the impact of charged current neutrino processes on the formation and evolution of neutrino spectra during the deleptonization of proto-neutron stars. To this end we develop the full kinematics of these reaction rates consistent with the nuclear equation of state, including weak magnetism contributions. This allows us to systematically study the impact of inelastic contributions and weak magnetism on the $ν_e$ and $\barν_e$ luminosities and average energies. Furthermore, we explore the role of the inverse neutron decay, also known as the direct Urca process, on the emitted spectra of $\barν_e$. This process is commonly considered in the cooling scenario of cold neutron stars but has so far been neglected in the evolution of hot proto-neutron stars. We find that the inverse neutron decay becomes the dominating opacity source for low-energy $\barν_e$. Accurate three-flavor Boltzmann neutrino transport enables us to relate the magnitude of neutrino fluxes and spectra to details of the treatment of weak processes. This allows us to quantify the corresponding impact on the conditions relevant for the nucleosynthesis in the neutrino-driven wind, which is ejected from the proto-neutron star surface during the deleptonization phase.

astro-ph.HE↗

arXiv2020

Neutrino Production Associated with Late Bumps in Gamma-Ray Bursts and Potential Contribution to Diffuse Flux at IceCube

IceCube has detected many TeV--PeV neutrinos, but their astrophysical origins remain largely unknown. Motivated by the observed late-time X-ray/optical bumps in some gamma-ray bursts (GRBs), we examine the correlation between IceCube neutrinos and GRBs allowing delayed neutrinos $\sim$days after the prompt gamma rays. Although we have not found any definitive correlation, up to $\sim$10\% of the events observed so far at IceCube may have been neutrinos produced by the late-time GRB activities at $\sim$1 day. Assuming a connection between some IceCube events and the late GRB bumps, we show in a model-independent way that GRB sites capable of producing late $\sim$PeV neutrinos should be nonrelativistic or mildly relativistic. We estimate the diffuse neutrino flux from such sources and find that they can possibly account for a few IceCube events. Future observations of high-energy neutrinos and late-time GRB afterglows can further test the above proposed connection.

astro-ph.HE↗

arXiv2019

A Versatile and Accurate Method for Halo Mass Determination from Phase-Space Distribution of Satellite Galaxies

We propose a versatile and accurate method to estimate the halo mass and concentration from the kinematics of satellite galaxies. We construct the 6D phase-space distribution function of satellites from a cosmological simulation based on the similarity of internal dynamics for different halos. Within the Bayesian statistical framework, not only can we infer the halo mass and concentration efficiently, but also treat various observational effects, including the selection function, incomplete data, and measurement errors, in a rigorous and straightforward manner. Through tests with mock samples, we show that our method is valid and accurate, and more precise than pure steady-state methods. It can constrain the halo mass to within ~ 20% using only 20 tracers and has a small intrinsic uncertainty of ~ 10%. In addition to the clear application to the Milky Way and similar galaxies, our method can be extended to galaxy groups or clusters.

astro-ph.GA↗

arXiv2019

New \textsl{s}-process Mechanism in Rapidly-Rotating Massive Pop II Stars

We report a new mechanism for the \textsl{s} in rotating massive metal-poor stars. Our models show that above a critical rotation speed, such stars evolve in a quasi-chemically-homogeneous fashion, which gives rise to a prolific \textsl{s}-process. Rotation-induced mixing results in primary production of $^{13}$C, which subsequently makes neutrons via $^{13}\mathrm{C}(α,\mathrm{n})^{16}\mathrm{O}$ during core He burning. Neutron capture can last up to $\sim 10^{13}\,\mathrm{s}$ ($\sim 3\times 10^{5}$~yr) with the peak central neutron density ranging from $\sim10^7$ to $10^{8}\,\mathrm{cm}^{-3}$. Depending on the rotation speed and the mass loss rate, a strong \textsl{s} can occur with production of elements up to Bi for progenitors with initial metallicities of $[Z]\lesssim -1.5$. This result suggests that rapidly-rotating massive metal-poor stars are likely the first site for the main \textsl{s}-process. We find that these stars can potentially explain the early onset of the \textsl{s}-process and some of the carbon-enhanced metal-poor (CEMP-\textsl{s} and CEMP-\textsl{r/s}) stars with strong enrichment attributed to the \textsl{s} or a mixture of the \textsl{r}-process and the \textsl{s}-process.

astro-ph.SR↗

arXiv2019

Presupernova neutrino signals as potential probes of neutrino mass hierarchy

We assess the potential of using presupernova neutrino signals at the Jiangmen Underground Neutrino Observatory (JUNO) to probe the yet-unknown neutrino mass hierarchy. Using models for stars of 12, 15, 20, and 25 solar masses, we find that if the electron antineutrino signals from such a star can be predicted precisely and the star is within ~440-880 pc, the number of events of electron antineutrino captures on protons detected within one day of its explosion allows to determine the hierarchy at the > ~95% confidence level. For determination at this level using such signals from Betelgeuse, which is at a distance of ~222 pc, the uncertainty in the predicted number of signals needs to be < ~14-30%. In view of more realistic uncertainties, we discuss and advocate a model-independent determination using both electron neutrino and antineutrino signals from Betelgeuse. This method is feasible if the cosmogenic background for neutrino-electron scattering events can be reduced by a factor of ~2.5-10 from the current estimate. Such reduction might be achieved by using coincidence of the background events, the exploration of which for JUNO is highly desirable.

astro-ph.HE↗

arXiv2019

Active-sterile Neutrino Oscillations in Neutrino-driven Winds: Implications for Nucleosynthesis

A protoneutron star produced in a core-collapse supernova (CCSN) drives a wind by its intense neutrino emission. We implement active-sterile neutrino oscillations in a steady-state model of this neutrino-driven wind to study their effects on the dynamics and nucleosynthesis of the wind in a self-consistent manner. Using vacuum mixing parameters indicated by some experiments for a sterile $ν_s$ of $\sim 1$ eV in mass, we observe interesting features of oscillations due to various feedback. For the higher $ν_s$ mass values, we find that oscillations can reduce the mass loss rate and the wind velocity by a factor of $\sim 1.6$--2.7 and change the electron fraction critical to nucleosynthesis by a significant to large amount. In the most dramatic cases, oscillations shifts nucleosynthesis from dominant production of $^{45}$Sc to that of $^{86}$Kr and $^{90}$Zr during the early epochs of the CCSN evolution.

astro-ph.HE↗

arXiv2019

Rate of dark photon emission from electron positron annihilation in massive stars

We calculate the rate of production of dark photons from electron-positron pair annihilation in hot and dense matter characteristic of supernova progenitors. Given the non-linear dependence of the emission rate on the dark photon mass and current astrophysical constraints on the dark photon parameter space, we focus on the mass range of 1--10 MeV. For the conditions under consideration both mixing with the in-medium photon and plasma effects on the electron dispersion relation are non-negligible and are explored in detail. We perform our calculations to the leading order in the fine-structure constant. Transverse and longitudinal photon modes are treated separately given their different dispersion relations. We consider the implications for the evolution of massive stars when dark photons decay either into particles of the standard model or of the dark sector.

hep-ph↗

arXiv2018

$s$-Process in Massive Carbon-Enhanced Metal-Poor Stars

Observations suggest that the interstellar medium (ISM) might have been highly enriched in carbon at very early times. We explore nucleosynthesis in massive carbon-enhanced metal-poor (CEMP) stars of $12$--$40\,\mathrm{M}_\odot$ formed from such an ISM with ${\rm [Fe]}\leq-2$. We find substantial production of elements heavier than Fe, mostly up to Sr, by the weak \textsl{s}-process in stars with initial abundances of ${\rm [CNO]}\gtrsim-1.5$. Even heavier elements, up to Ba, can be produced for ${\rm [CNO]}\gtrsim-0.5$. The efficiency of this \textsl{s}-process is sensitive to the initial enhancement of C (or more generally, CNO) and mass of the star, with the yield increasing approximately linearly with the initial Fe abundance. The \textsl{s}-process in CEMP stars of $\gtrsim 20 \,\mathrm{M}_\odot$ with ${\rm [CNO]}\gtrsim -1.5$ can be an important source for heavy elements in the Early Galaxy.

astro-ph.SR↗

arXiv2018

New Neutron-Capture Site in Massive Pop III and Pop II Stars as a Source for Heavy Elements in the Early Galaxy

We propose a new neutron-capture site in early metal-poor and metal-free stars of $\sim 20$--$30 \,\mathrm{M}_\odot$ that results from proton ingestion in the He shell during late stages of the stars' lives. Most of the neutron capture occurs in the first $\lesssim 10^6\,$s following proton ingestion when $^{13}{\rm C}(α,\mathrm{n})^{16}\mathrm{O}$ produces neutron densities typical of the intermediate neutron-capture process. This phase may be followed by another lasting $\gtrsim 10^7\,$s with $^{17}\mathrm{O}(α,\mathrm{n})^{20}\mathrm{Ne}$ producing much lower neutron densities typical of the slow neutron-capture process. We explore the dependence of the proposed neutron-capture nucleosynthesis on the amount and time of proton ingestion, the initial metallicity, and the ensuing supernova shock. We obtain a range of heavy element abundance patterns including those attributed to the slow neutron-capture process or a combination of the slow and rapid neutron-capture processes. Our results can account for the observed ubiquity of heavy elements such as Sr and Ba in the early Galaxy and explain puzzling abundance patterns of these elements in at least some very metal-poor (VMP) stars including those of the carbon-enhanced varieties. In the latter case, the explanation by the single site proposed here differs from the existing paradigm that attributes various classes of VMP stars to enrichment by multiple different sites.

astro-ph.SR↗

arXiv2018

Production of Mo and Ru isotopes in neutrino-driven winds: implications for solar abundances and presolar grains

The origin of the so-called $p$-isotopes $^{92,94}\mathrm{Mo}$ and $^{96,98}\mathrm{Ru}$ in the solar system remains a mystery as several astrophysical scenarios fail to account for them. In addition, data on presolar silicon carbide grains of type X (SiC X) exhibit peculiar Mo patterns, especially for $^{95,97}\mathrm{Mo}$. We examine production of Mo and Ru isotopes in neutrino-driven winds associated with core-collapse supernovae (CCSNe) over a wide range of conditions. We find that proton-rich winds can make dominant contributions to the solar abundance of $^{98}\mathrm{Ru}$, significant contributions to those of $^{96}$Ru ($\lesssim 40\%$) and $^{92}$Mo ($\lesssim 27\%$), and relatively minor contributions to that of $^{94}$Mo ($\lesssim 14\%$). In contrast, neutron-rich winds make negligible contributions to the solar abundances of $^{92,94}$Mo and cannot produce $^{96,98}$Ru. However, we show that some neutron-rich winds can account for the peculiar Mo patterns in SiC X grains. Our results can be generalized if conditions similar to those studied here are also obtained for other types of ejecta in either CCSNe or neutron star mergers.

astro-ph.HE↗

arXiv2018

Neutrinos, supernovae, and the origin of the heavy elements

Stars of ~8-100 solar masses end their lives as core-collapse supernovae (SNe). In the process they emit a powerful burst of neutrinos, produce a variety of elements, and leave behind either a neutron star or a black hole. The wide mass range for SN progenitors results in diverse neutrino signals, explosion energies, and nucleosynthesis products. A major mechanism to produce nuclei heavier than iron is rapid neutron capture, or the r process. This process may be connected to SNe in several ways. A brief review is presented on current understanding of neutrino emission, explosion, and nucleosynthesis of SNe.

astro-ph.HE↗

arXiv2017

Determination of Dark Matter Halo Mass from Dynamics of Satellite Galaxies

We show that the mass of a dark matter halo can be inferred from the dynamical status of its satellite galaxies. Using 9 dark-matter simulations of halos like the Milky Way (MW), we find that the present-day substructures in each halo follow a characteristic distribution in the phase space of orbital binding energy and angular momentum, and that this distribution is similar from halo to halo but has an intrinsic dependence on the halo formation history. We construct this distribution directly from the simulations for a specific halo and extend the result to halos of similar formation history but different masses by scaling. The mass of an observed halo can then be estimated by maximizing the likelihood in comparing the measured kinematic parameters of its satellite galaxies with these distributions. We test the validity and accuracy of this method with mock samples taken from the simulations. Using the positions, radial velocities, and proper motions of 9 tracers and assuming observational uncertainties comparable to those of MW satellite galaxies, we find that the halo mass can be recovered to within $\sim$40%. The accuracy can be improved to within $\sim$25% if 30 tracers are used. However, the dependence of the phase-space distribution on the halo formation history sets a minimum uncertainty of $\sim$20% that cannot be reduced by using more tracers. We believe that this minimum uncertainty also applies to any mass determination for a halo when the phase space information of other kinematic tracers is used.

astro-ph.GA↗

arXiv2016

Evidence from stable isotopes and Be-10 for solar system formation triggered by a low-mass supernova

About 4.6 billion years ago, some event disturbed a cloud of gas and dust, triggering the gravitational collapse that led to the formation of the solar system. A core-collapse supernova, whose shock wave is capable of compressing such a cloud, is an obvious candidate for the initiating event. This hypothesis can be tested because supernovae also produce telltale patterns of short-lived radionuclides, which would be preserved today as isotopic anomalies. Previous studies of the forensic evidence have been inconclusive, finding a pattern of isotopes differing from that produced in conventional supernova models. Here we argue that these difficulties either do not arise or are mitigated if the initiating supernova was a special type, low in mass and explosion energy. Key to our conclusion is the demonstration that short-lived Be-10 can be readily synthesized in such supernovae by neutrino interactions, while anomalies in stable isotopes are suppressed.

astro-ph.SR↗