arXiv subjects

Yu-Yang Wang

Publications and source records attributed to Yu-Yang Wang.

4 recordsLinked to original sources

arXiv2024

Spin Symmetry in Thermally-Assisted-Occupation Density Functional Theory

For electronic systems with multi-reference (MR) character, Kohn-Sham density functional theory (KS-DFT) with the conventional exchange-correlation (xc) energy functionals can lead to incorrect spin densities and related properties. For example, for H2 dissociation, the spin-restricted and spin-unrestricted solutions obtained with the same xc energy functional in KS-DFT can be distinctly different, yielding the unphysical spin-symmetry breaking effects in the spin-unrestricted solutions. Recently, thermally-assisted-occupation density functional theory (TAO-DFT) has been shown to resolve the aforementioned spin-symmetry breaking, when the fictitious temperature is properly chosen. In this work, a response theory based on TAO-DFT is developed to demonstrate that TAO-DFT with a sufficiently large fictitious temperature can always resolve the unphysical spin-symmetry breaking in MR systems. To further support this, TAO-DFT calculations with various fictitious temperatures are performed for the dissociation of H2, N2, He2, and Ne2 as well as the twisted ethylene.

physics.chem-ph↗

arXiv2023

The Apertif Radio Transient System (ARTS): Design, Commissioning, Data Release, and Detection of the first 5 Fast Radio Bursts

Fast Radio Bursts must be powered by uniquely energetic emission mechanisms. This requirement has eliminated a number of possible source types, but several remain. Identifying the physical nature of Fast Radio Burst (FRB) emitters arguably requires good localisation of more detections, and broadband studies enabled by real-time alerting. We here present the Apertif Radio Transient System (ARTS), a supercomputing radio-telescope instrument that performs real-time FRB detection and localisation on the Westerbork Synthesis Radio Telescope (WSRT) interferometer. It reaches coherent-addition sensitivity over the entire field of the view of the primary dish beam. After commissioning results verified the system performed as planned, we initiated the Apertif FRB survey (ALERT). Over the first 5 weeks we observed at design sensitivity in 2019, we detected 5 new FRBs, and interferometrically localised each of these to 0.4--10 sq. arcmin. All detections are broad band and very narrow, of order 1 ms duration, and unscattered. Dispersion measures are generally high. Only through the very high time and frequency resolution of ARTS are these hard-to-find FRBs detected, producing an unbiased view of the intrinsic population properties. Most localisation regions are small enough to rule out the presence of associated persistent radio sources. Three FRBs cut through the halos of M31 and M33. We demonstrate that Apertif can localise one-off FRBs with an accuracy that maps magneto-ionic material along well-defined lines of sight. The rate of 1 every ~7 days next ensures a considerable number of new sources are detected for such study. The combination of detection rate and localisation accuracy exemplified by the 5 first ARTS FRBs thus marks a new phase in which a growing number of bursts can be used to probe our Universe.

astro-ph.HE↗

arXiv2021

X-ray Plateaus in Gamma-Ray Burst Afterglows and Their Application in Cosmology

For gamma-ray bursts (GRBs) with a plateau phase in the X-ray afterglow, a so called $L-T-E$ correlation has been found which tightly connects the isotropic energy of the prompt GRB ($E_{γ,\rm{iso}}$) with the end time of the X-ray plateau ($T_{a}$) and the corresponding X-ray luminosity at the end time ($L_{X}$). Here we show that there is a clear redshift evolution in the correlation. Furthermore, since the power-law indices of $L_{X}$ and $E_{γ,\rm{iso}}$ in the correlation function are almost identical, the $L-T-E$ correlation is insensitive to cosmological parameters and cannot be used as a satisfactory standard candle. On the other hand, based on a sample including 121 long GRBs, we establish a new three parameter correlation that connects $L_{X}$, $T_{a}$ and the spectral peak energy $E_{\rm{p}}$, i.e. the $L-T-E_{\rm{p}}$ correlation. This correlation strongly supports the so-called Combo-relation established by Izzo et al. (2015). After correcting for the redshift evolution, we show that the de-evolved $L-T-E_{\rm{p}}$ correlation can be used as a standard candle. By using this correlation alone, we are able to constrain the cosmological parameters as $Ω_{m}=0.389^{+0.202}_{-0.141}$ ($1σ$) for the flat $Λ$CDM model, or $Ω_{m}=0.369^{+0.217}_{-0.191}$, $w=-0.966^{+0.513}_{-0.678}$ ($1σ$) for the flat $w$CDM model. Combining with other cosmological probes, more accurate constraints on the cosmology models are presented.

astro-ph.HE↗

arXiv2019

Calibration of gamma-ray bursts luminosity correlations using gravitational waves as standard sirens

Gamma-ray bursts (GRBs) are a potential tool to probe high-redshift universe. However, the circularity problem enforces people to find model-independent methods to study the luminosity correlations of GRBs. Here, we present a new method which uses gravitational waves as standard sirens to calibrate GRB luminosity correlations. For the third-generation ground-based GW detectors (i.e., Einstein Telescope), the redshifts of gravitational wave (GW) events accompanied electromagnetic counterparts can reach out to $\sim 4$, which is more distant than type Ia supernovae ($z\lesssim 2$). The Amati relation and Ghirlanda relation are calibrated using mock GW catalogue from Einstein Telescope. We find that the $1σ$ uncertainty of intercepts and slopes of these correlations can be constrained to less than 0.2\% and 8\% respectively. Using calibrated correlations, the evolution of dark energy equation of state can be tightly measured, which is important for discriminating dark energy models.

astro-ph.HE↗