arXiv subjects

W. Cui

Publications and source records attributed to W. Cui.

At least 37 records · Page 2Linked to original sources

arXiv2023

The Three Hundred project: A Machine Learning method to infer clusters of galaxies mass radial profiles from mock Sunyaev-Zel'dovich maps

We develop a machine learning algorithm to infer the 3D cumulative radial profiles of total and gas mass in galaxy clusters from thermal Sunyaev-Zel'dovich effect maps. We generate around 73,000 mock images along various lines of sight using 2,522 simulated clusters from the \thethreehundred{} project at redshift $z< 0.12$ and train a model that combines an autoencoder and a random forest. Without making any prior assumptions about the hydrostatic equilibrium of the clusters, the model is capable of reconstructing the total mass profile as well as the gas mass profile, which is responsible for the SZ effect. We show that the recovered profiles are unbiased with a scatter of about $10\%$, slightly increasing towards the core and the outskirts of the cluster. We selected clusters in the mass range of $10^{13.5} \leq M_{200} /(\hMsun) \leq 10^{15.5}$, spanning different dynamical states, from relaxed to disturbed halos. We verify that both the accuracy and precision of this method show a slight dependence on the dynamical state, but not on the cluster mass. To further verify the consistency of our model, we fit the inferred total mass profiles with an NFW model and contrast the concentration values with those of the true profiles. We note that the inferred profiles are unbiased for higher concentration values, reproducing a trustworthy mass-concentration relation. The comparison with a widely used mass estimation technique, such as hydrostatic equilibrium, demonstrates that our method recovers the total mass that is not biased by non-thermal motions of the gas.

astro-ph.CO↗

arXiv2022

X-ray morphology due to charge-exchange emissions used to study the global structure around Mars

Soft x-ray emissions induced by solar wind ions that collide with neutral material in the solar system have been detected around planets, and were proposed as a remote probe for the solar wind interaction with the Martian exosphere. A multi-fluid three-dimensional magneto-hydrodynamic model is adopted to derive the global distributions of solar wind particles. Spherically symmetric exospheric H, H$_2$, He, O, and CO$_2$ density profiles and a sophisticated hybrid model that includes charge-exchange and proton/neutral excitation processes are used to study the low triplet line ratio $G=\frac{i+f}{r}$ (0.77$\pm$0.58) of O VII and total x-ray luminosity around Mars. We further calculate the emission factor $α$-value with different neutrals over a wide ion abundance and velocity ranges. Our results are in good agreement with those of previous reports. The evolution of the charge stage of solar wind ions shows that sequential recombination due to charge-exchange can be negligible at the interaction region. This only appears below the altitude of 400~km. The anonymous low disk $G$ ratio can be easily explained by the collisional quenching effect at neutral densities higher than 10$^{11}$cm$^{-3}$. However, the quenching contribution is small in Mars' exosphere and only appears below 400~km. Charge-exchange with H$_2$ and N$_2$ is still the most likely reason for this low $G$-ratio. X-ray emissivity maps in collisions with different neutrals differ from each other. A clear bow shock in the collision with all the neutrals is in accordance with previous reports. The resulting total x-ray luminosity of 6.55~MW shows a better agreement with the XMM-Newton observation of 12.8$\pm$1.4~MW than that of previous predictions.

astro-ph.EP↗

arXiv2022

Shocks in the Stacked Sunyaev-Zel'dovich Profiles of Clusters II: Measurements from SPT-SZ + Planck Compton-y Map

We search for the signature of cosmological shocks in stacked gas pressure profiles of galaxy clusters using data from the South Pole Telescope (SPT). Specifically, we stack the latest Compton-y maps from the 2500 deg^2 SPT-SZ survey on the locations of clusters identified in that same dataset. The sample contains 516 clusters with mean mass = 1e14.9 msol and redshift = 0.55. We analyze in parallel a set of zoom-in hydrodynamical simulations from The Three Hundred project. The SPT-SZ data show two features: (i) a pressure deficit at R/R200m = $1.08 \pm 0.09$, measured at $3.1σ$ significance and not observed in the simulations, and; (ii) a sharp decrease in pressure at R/R200m = $4.58 \pm 1.24$ at $2.0σ$ significance. The pressure deficit is qualitatively consistent with a shock-induced thermal non-equilibrium between electrons and ions, and the second feature is consistent with accretion shocks seen in previous studies. We split the cluster sample by redshift and mass, and find both features exist in all cases. There are also no significant differences in features along and across the cluster major axis, whose orientation roughly points towards filamentary structure. As a consistency test, we also analyze clusters from the Planck and Atacama Cosmology Telescope Polarimeter surveys and find quantitatively similar features in the pressure profiles. Finally, we compare the accretion shock radius (Rsh_acc) with existing measurements of the splashback radius (Rsp) for SPT-SZ and constrain the lower limit of the ratio, Rsh_acc/Rsp > $2.16 \pm 0.59$.

astro-ph.CO↗

arXiv2021

The Three Hundred-NIKA2 Sunyaev-Zeldovich Large Program twin samples: Synthetic clusters to support real observations

The simulation database of THE THREE HUNDRED Project has been used to pick synthetic clusters of galaxies with properties close to the observational targets of the NIKA2 camera Sunyaev-Zeldovich (SZ) Large Program. Cross-matching of cluster parameters such as mass and redshift of the cluster in the two databases has been implemented to generate the so-called twin samples for the Large Program. This SZ Large Program is observing a selection of galaxy clusters at intermediate and high redshift $\left( 0.5 < z < 0.9 \right)$, covering one order of magnitude in mass. These are SZ-selected clusters from the Planck and Atacama Cosmology Telescope catalogs, wherein the selection is based on their integrated Compton parameter values, $Y_{500}$: the value of the parameter within the characteristics radius $R_{500}$. THE THREE HUNDRED hydrodynamical simulations provide us with hundreds of clusters satisfying these redshift, mass, and $Y_{500}$ requirements. In addition to the standard post-processing analysis of the simulation, mock observational maps are available mimicking X-ray, optical, gravitational lensing, radio, and SZ observations of galaxy clusters. The primary goal of employing the twin samples is to compare different cluster mass proxies from synthetic X-ray, SZ effect and optical maps (via the velocity dispersion of member galaxies and lensing $κ$-maps) of the clusters. Eventually, scaling laws between different mass proxies and the cluster mass will be cross-correlated to reduce the scatter on the inferred mass and the mass bias will be related to various physical parameters.

astro-ph.CO↗

arXiv2021

Cosmic filaments delay quenching inside clusters

We investigate how large-scale cosmic filaments impact the quenching of galaxies within one virial radius of 324 simulated clusters from The Three Hundred project. We track cosmic filaments with the versatile, observation-friendly program DisPerSE and identify halos hosting galaxies with VELOCIRaptor. We find that cluster galaxies close to filaments tend to be more star-forming, bluer, and contain more cold gas than their counterparts further away from filaments. This effect is recovered at all stellar masses. This is in stark contrast with galaxies residing outside of clusters, where galaxies close to filaments show clear signs of density related pre-processing. We first show that the density contrast of filaments is reduced inside the intra-cluster medium. Moreover, examination of flows around and into cluster galaxies shows that the gas flows in intra-cluster filaments are colder and tend to stream along with galaxies in their midst, partially shielding them from strangulation by the hot, dense intra-cluster medium. This also preserves accretion onto satellites and limit ram pressure.

astro-ph.GA↗

arXiv2021

HXMT Identification of a non-thermal X-ray burst from SGR J1935+2154 and with FRB 200428

Fast radio bursts (FRBs) are short pulses observed in radio band from cosmological distances. One class of models invoke soft gamma-ray repeaters (SGRs), or magnetars, as the sources of FRBs. Some radio pulses have been observed from some magnetars, however, no FRB-like events had been detected in association any magnetar burst, including one giant flare. Recently, a pair of FRB-like bursts (FRB 200428 hereafter) separated by milliseconds (ms) were detected from the general direction of the Galactic magnetar SGR J1935+2154. Here we report the detection of a non-thermal X-ray burst in the 1-250 keV energy band with the Insight-HXMT satellite, which we identify as emitted from SGR J1935+2154. The burst showed two hard peaks with a separation of 34 ms, broadly consistent with that of the two bursts in FRB 200428. The delay time between the double radio and X-ray peaks is about 8.57 s, fully consistent with the dispersion delay of FRB 200428. We thus identify the non-thermal X-ray burst is associated with FRB 200428 whose high energy counterpart is the two hard peaks in X-ray. Our results suggest that the non-thermal X-ray burst and FRB 200428 share the same physical origin in an explosive event from SGR J1935+2154.

astro-ph.HE↗

arXiv2021

Carbon nanotubes collapse phase diagram with arbitrary number of walls. Collapse modes and macroscopic analog

Carbon nanotubes tend to collapse when their diameters exceed a certain threshold, or when a sufficiently large external pressure is applied on their walls. Their radial stability of tubes has been studied in each of these cases, however a general theory able to predict collapse is still lacking. Here, we propose a simple model predicting stability limits as a function of the tube diameter, the number of walls and the pressure. The model is supported by atomistic simulations, experiments, and is used to plot collapse phase diagrams. We have identified the most stable carbon nanotube, which can support a maximum pressure of 18 GPa before collapsing. The latter was identified as a multiwall tube with an internal tube diameter of 12nm and 30 walls. This maximum pressure is lowered depending on the internal tube diameter and the number of walls. We then identify a tube diameter domain in which the radial mechanical stability can be treated as equivalent to macroscopic tubes, known to be described by the canonical Lévy-Carrier law. This multiscale behavior is shown to be in good agreement with experiments based on O-ring gaskets collapse, proposed as a simple macroscopic parallel to nanotubes in this domain.

physics.comp-ph↗

arXiv2020

Insight-HXMT observations of Swift J0243.6+6124: the evolution of RMS pulse fractions at super-Eddington luminosity

Based on Insight-HXMT data, we report on the pulse fraction evolution during the 2017-2018 outburst of the newly discovered first Galactic ultraluminous X-ray source (ULX) Swift J0243.6+6124. The pulse fractions of 19 observation pairs selected in the rising and fading phases with similar luminosity are investigated. The results show a general trend of the pulse fraction increasing with luminosity and energy at super-critical luminosity. However, the relative strength of the pulsation between each pair evolves strongly with luminosity. The pulse fraction in the rising phase is larger at luminosity below $7.71\times10^{38}$~erg~s$^{-1}$, but smaller at above. A transition luminosity is found to be energy independent. Such a phenomena is firstly confirmed by Insight-HXMT observations and we speculate it may have relation with the radiation pressure dominated accretion disk.

astro-ph.HE↗

arXiv2020

Constraining the cross-section of dark matter with giant radial arcs in galaxy clusters

We compare the statistics and morphology of giant arcs in galaxy clusters using N-body and non-radiative SPH simulations within the standard cold dark matter model and simulations where dark matter has a non-negligible probability of interaction (parametrized by its cross-section), i.e self-interacting dark matter (SIDM). We use a ray-tracing technique to produce a statistically large number of arcs around six simulated galaxy clusters at different redshifts. Since dark matter is more likely to interact in colliding clusters than in relaxed clusters, and this probability of interaction is largest in denser regions, we focus our analysis on radial arcs (which trace the lensing potential in the central region better than tangential arcs) in galaxy clusters which underwent (or are undergoing) a major merger. We find that self-interacting dark matter produces fewer radial arcs than standard cold dark matter but they are on average more magnified. We also appreciate differences in the arc morphology that could be used to statistically favor one model versus the other.

astro-ph.CO↗

arXiv2020

Do model emission line galaxies live in filaments at z~1?

Current and future cosmological surveys are targeting star-forming galaxies at $z\sim 1$ with nebular emission lines. We use a state-of-the-art semi-analytical model of galaxy formation and evolution to explore the large scale environment of star-forming emission line galaxies (ELGs). Model ELGs are selected such that they can be compared directly with the DEEP2, VVDS, eBOSS-SGC and DESI surveys. The large scale environment of the ELGs is classified using velocity-shear-tensor and tidal-tensor algorithms. Half of the model ELGs live in filaments and about a third in sheets. Model ELGs which reside in knots have the largest satellite fractions. We find that the shape of the mean halo occupation distribution of model ELGs varies widely for different large scale environments. To interpret our results, we also study fixed number density samples of ELGs and galaxies selected using simpler criteria, with single cuts in stellar mass, star formation rate and [OII] luminosity. The fixed number density ELG selection produces samples that are close to L[OII] and SFR selected samples for densities above $10^{-4.2}h^{3}{\rm Mpc}^{-3}$. ELGs with an extra cut in stellar mass applied to fix their number density, present differences in sheets and knots with respect to the other samples. ELGs, SFR and L[OII] selected samples with equal number density have similar large scale bias but their clustering below separations of $1h^{-1}$Mpc is different.

astro-ph.GA↗

arXiv2020

Insight-HXMT firm detection of the highest energy fundamental cyclotron resonance scattering feature in the spectrum of GRO J1008-57

We report on the observation of the accreting pulsar GRO J1008-57 performed by Insight-HXMT at the peak of the source's 2017 outburst. Pulsations are detected with a spin period of 93.283(1) s. The pulse profile shows double peaks at soft X-rays, and only one peak above 20 keV. The spectrum is well described by the phenomenological models of X-ray pulsars. A cyclotron resonant scattering feature is detected with very high statistical significance at a centroid energy of $E_{\rm cyc}=90.32_{-0.28}^{+0.32}$ keV, for the reference continuum and line models, HIGHECUT and GABS respectively. Detection is very robust with respect to different continuum models. The line energy is significantly higher than what suggested from previous observations, which provided very marginal evidence for the line. This establishes a new record for the centroid energy of a fundamental cyclotron resonant scattering feature observed in accreting pulsars. We also discuss the accretion regime of the source during the Insight-HXMT observation.

astro-ph.HE↗

arXiv2020

Insight-HXMT insight into switch of the accretion mode: the case of the X-ray pulsar 4U 1901+03

We use the In data collected during the 2019 outburst from X-ray pulsar 4U 1901+03 to complement the orbital parameters reported by Fermi/GBM. Using the Insight-HXMT, we examine the correlation between the derivative of the intrinsic spin frequency and bolometric flux based on accretion torque models. It was found that the pulse profiles significantly evolve during the outburst. The existence of two types of the profile's pattern discovered in the Insight-HXMT data indicates that this source experienced transition between a super-critical and a sub-critical accretion regime during its 2019 outburst. Based on the evolution of the pulse profiles and the torque model, we derive the distance to 4U 1901+03 as 12.4+-0.2 kpc.

astro-ph.HE↗

arXiv2020

The evolution of the broadband temporal features observed in the black-hole transient MAXI J1820+070 with Insight-HXMT

We study the evolution of the temporal properties of MAXI 1820+070 during the 2018 outburst in its hard state from MJD 58190 to 58289 with Insight-HXMT in a broad energy band 1-150 keV. We find different behaviors of the hardness ratio, the fractional rms and time lag before and after MJD 58257, suggesting a transition occurred at around this point. The observed time lags between the soft photons in the 1-5 keV band and the hard photons in higher energy bands, up to 150 keV, are frequency-dependent: the time lags in the low-frequency range, 2-10 mHz, are both soft and hard lags with a timescale of dozens of seconds but without a clear trend along the outburst; the time lags in the high-frequency range, 1-10 Hz, are only hard lags with a timescale of tens of milliseconds; first increase until around MJD 58257 and decrease after this date. The high-frequency time lags are significantly correlated to the photon index derived from the fit to the quasi-simultaneous NICER spectrum in the 1-10 keV band. This result is qualitatively consistent with a model in which the high-frequency time lags are produced by Comptonization in a jet.

astro-ph.HE↗

arXiv2020

Discovery of delayed spin-up behavior following two large glitches in the Crab pulsar, and the statistics of such processes

Glitches correspond to sudden jumps of rotation frequency ($ν$) and its derivative ($\dotν$) of pulsars, the origin of which remains not well understood yet, partly because the jump processes of most glitches are not well time-resolved. There are three large glitches of the Crab pulsar, detected in 1989, 1996 and 2017, which were found to have delayed spin-up processes before the normal recovery processes. Here we report two additional glitches of the Crab pulsar occurred in 2004 and 2011 for which we discovered delayed spin up processes, and present refined parameters of the largest glitch occurred in 2017. The initial rising time of the glitch is determined as $<0.48$ hour. We also carried out a statistical study of these five glitches with observed spin-up processes. The two glitches occurred in 2004 and 2011 have delayed spin-up time scales ($τ_{1}$) of $1.7\pm0.8$\,days and $1.6\pm0.4$\,days, respectively. We find that the $Δν$ vs. $|Δ{\dotν}|$ relation of these five glitches is similar to those with no detected delayed spin-up process, indicating that they are similar to the others in nature except that they have larger amplitudes. For these five glitches, the amplitudes of the delayed spin-up process ($|Δν_{\rm d1}|$) and recovery process ($Δν_{\rm d2}$), their time scales ($τ_{1}$, $τ_{2}$), and permanent changes in spin frequency ($Δν_{\rm p}$) and total frequency step ($Δν_{\rm g}$) have positive correlations. From these correlations, we suggest that the delayed spin-up processes are common for all glitches, but are too short and thus difficult to be detected for most glitches.

astro-ph.HE↗

arXiv2020

Evidence for proton acceleration up to TeV energies based on VERITAS and Fermi-LAT observations of the Cas A SNR

We present a study of $γ$-ray emission from the core-collapse supernova remnant Cas~A in the energy range from 0.1GeV to 10TeV. We used 65 hours of VERITAS data to cover 200 GeV - 10 TeV, and 10.8 years of \textit{Fermi}-LAT data to cover 0.1-500 GeV. The spectral analysis of \textit{Fermi}-LAT data shows a significant spectral curvature around $1.3 \pm 0.4_{stat}$ GeV that is consistent with the expected spectrum from pion decay. Above this energy, the joint spectrum from \textit{Fermi}-LAT and VERITAS deviates significantly from a simple power-law, and is best described by a power-law with spectral index of $2.17\pm 0.02_{stat}$ with a cut-off energy of $2.3 \pm 0.5_{stat}$ TeV. These results, along with radio, X-ray and $γ$-ray data, are interpreted in the context of leptonic and hadronic models. Assuming a one-zone model, we exclude a purely leptonic scenario and conclude that proton acceleration up to at least 6 TeV is required to explain the observed $γ$-ray spectrum. From modeling of the entire multi-wavelength spectrum, a minimum magnetic field inside the remnant of $B_{\mathrm{min}}\approx150\,\mathrm{μG}$ is deduced.

astro-ph.HE↗

arXiv2020

A search for prompt gamma-ray counterparts to fast radio bursts in the Insight-HXMT data

No robust detection of prompt electromagnetic counterparts to fast radio bursts (FRBs) has yet been obtained, in spite of several multi-wavelength searches carried out so far. Specifically, X/gamma-ray counterparts are predicted by some models. We planned on searching for prompt gamma-ray counterparts in the Insight-Hard X-ray Modulation Telescope (Insight-HXMT) data, taking advantage of the unique combination of large effective area in the keV-MeV energy range and of sub-ms time resolution. We selected 39 FRBs that were promptly visible from the High-Energy (HE) instrument aboard Insight-HXMT. After calculating the expected arrival times at the location of the spacecraft, we searched for a significant excess in both individual and cumulative time profiles over a wide range of time resolutions, from several seconds down to sub-ms scales. Using the dispersion measures in excess of the Galactic terms, we estimated the upper limits on the redshifts. No convincing signal was found and for each FRB we constrained the gamma-ray isotropic-equivalent luminosity and the released energy as a function of emission timescale. For the nearest FRB source, the periodic repeater FRB180916.J0158+65, we find $L_{γ,iso}<5.5\times 10^{47}$ erg/s over 1 s, whereas $L_{γ,iso}<10^{49}-10^{51}$ erg/s for the bulk of FRBs. The same values scale up by a factor of ~100 for a ms-long emission. Even on a timescale comparable with that of the radio pulse itself no keV-MeV emission is observed. A systematic association with either long or short GRBs is ruled out with high confidence, except for subluminous events, as is the case for core-collapse of massive stars (long) or binary neutron star mergers (short) viewed off axis. Only giant flares from extra-galactic magnetars at least ten times more energetic than Galactic siblings are ruled out for the nearest FRB.

astro-ph.HE↗

arXiv2020

Switches between accretion structures during flares in 4U 1901+03

We report on our analysis of the 2019 outburst of the X-ray accreting pulsar 4U 1901+03 observed with Insight-HXMT and NICER. Both spectra and pulse profiles evolve significantly in the decaying phase of the outburst. Dozens of flares are observed throughout the outburst. They are more frequent and brighter at the outburst peak. We find that the flares, which have a duration from tens to hundreds of seconds, are generally brighter than the persistent emission by a factor of $\sim$ 1.5. The pulse profile shape during the flares can be significantly different than that of the persistent emission. In particular, a phase shift is clearly observed in many cases. We interpret these findings as direct evidence of changes of the pulsed beam pattern, due to transitions between the sub- and super-critical accretion regimes on a short time scale. We also observe that at comparable luminosities the flares' pulse profiles are rather similar to those of the persistent emission. This indicates that the accretion on the polar cap of the neutron star is mainly determined by the luminosity, i.e., the mass accretion rate.

astro-ph.HE↗

arXiv2020

A decade of multi-wavelength observations of the TeV blazar 1ES 1215+303: Extreme shift of the synchrotron peak frequency and long-term optical-gamma-ray flux increase

Blazars are known for their variability on a wide range of timescales at all wavelengths. Most studies of TeV gamma-ray blazars focus on short timescales, especially during flares. With a decade of observations from the Fermi-LAT and VERITAS, we present an extensive study of the long-term multi-wavelength radio-to-gamma-ray flux-density variability, with the addition of a couple of short-time radio-structure and optical polarization observations of the blazar 1ES 1215+303 (z=0.130), with a focus on its gamma-ray emission from 100 MeV to 30 TeV. Multiple strong GeV gamma-ray flares, a long-term increase in the gamma-ray and optical flux baseline and a linear correlation between these two bands are observed over the ten-year period. Typical HBL behaviors are identified in the radio morphology and broadband spectrum of the source. Three stationary features in the innermost jet are resolved by VLBA at 43.1, 22.2, and 15.3 GHz. We employ a two-component synchrotron self-Compton model to describe different flux states of the source, including the epoch during which an extreme shift in energy of the synchrotron peak frequency from infrared to soft X-rays is observed.

astro-ph.HE↗