分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Tidal disruption events (TDEs) that occur in active galactic nuclei (AGN) with dusty tori are a special class of sources. TDEs can generate ultrafast and large opening-angle wind, which will almost inevitably collide with the preexisting AGN dusty tori a few years later after the TDE outburst. The wind-torus interactions drive two kinds of shocks: the bow shocks at the windward side of the torus clouds, and the cloud shocks inside the torus clouds. In a previous work, we proved that the shocked clouds will give rise to considerable X-ray emissions which can reach $10^{41-42}$ erg s$^{-1}$ (so called \emph{years delayed X-ray afterglows}). In this work, we focus on the radiations of high energy particles accelerated at both shocks. Benefitting from the strong radiation field at the inner edge of the torus, the inverse Compton scatterings of AGN photons by relativistic electrons at bow shocks dominate the overall gamma-ray radiation. The gamma-ray luminosity can reach $10^{41}~{\rm erg s^{-1}} (L_{\rm kin}/10^{45}{\rm erg s^{-1}})$, where $L_{\rm kin}$ is the kinetic luminosity of TDE wind. Synchrotron radiation at bow shocks contributes to the radio afterglow with a luminosity of 10$^{38-39} ~{\rm erg s^{-1}} (L_{\rm kin}/10^{45}{\rm erg s^{-1}})$ at 1-10 GHz if the magnetic field is 100 mGauss, and extends to infrared with a luminosity of $\sim 10^{39-40}~{\rm erg s^{-1}} (L_{\rm kin}/10^{45}{\rm erg s^{-1}})$. Our scenario provides a prediction of the years delayed afterglows in multiple wavebands for TDEs and reveals their connections.
分类： 物理学 >> 核物理学 提交时间： 2016-09-18
摘要： A foremost task in understanding the nature of the X(3872) involves the discrimination of the two-quark and multiquark configurations. In this work, we propose a method to probe the short-distance component of the X(3872) by measuring the ratio between the Bc semileptonic and nonleptonic decays into the X(3872). We demonstrate that if the X(3872) production mechanism is through the c¯c component, the ratios would be universal and could be reliably predicted in theory. Measurements of these ratios at LHC and the next-generation electron-positron colliders are capable of validating/invalidating this production mechanism and providing deeper insights into the nature of the X(3872).
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We discuss the stochastic gravitational-wave spectrum from dark confinement and chiral phase transitions in the early Universe. Specifically, we look at pure Yang-Mills theory for an arbitrary number of colours as well as SU(3) with quarks in different representations. We utilise thermodynamic lattice data and map it to effective models, such as the Polyakov-loop and the PNJL model. This allows us to compute gravitational-wave parameters and the corresponding gravitational-wave signal. We compare the signal to future gravitational-wave observatories such as the Big Bang Observer and DECIGO.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Random sampling in high dimensions has successfully been applied to phenomena as diverse as nuclear resonances, neural networks and black hole evaporation. Here we revisit an elegant argument by the British physicist Dennis Sciama, which demonstrated that were our universe random, it would almost certainly have a negligible chance for life. Under plausible assumptions, we show that a random universe can masquerade as `intelligently designed,' with the fundamental constants instead appearing to be fined tuned to achieve the highest probability for life to occur. For our universe, this mechanism may only require there to be around a dozen currently unknown fundamental constants. More generally, this mechanism appears to be important for data science analysis on constrained sets. Finally, we consider wider applications.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： With the rapid development of deep learning technology, more and more researchers apply it to gravitational wave (GW) data analysis. Previous studies focused on a single deep learning model. In this paper we design an ensemble algorithm combining a set of convolutional neural networks (CNN) for GW signal recognition. The whole ensemble model consists of two sub-ensemble models. Each sub-ensemble model is also an ensemble model of deep learning. The two sub-ensemble models treat data of Hanford and Livinston detectors respectively. Proper voting scheme is adopted to combine the two sub-ensemble models to form the whole ensemble model. We apply this ensemble model to all reported GW events in the first observation and second observation runs (O1/O2) by LIGO-VIRGO Scientific Collaboration. We find that the ensemble algorithm can clearly identify all binary black hole merger events except GW170818. We also apply the ensemble model to one month (August 2017) data of O2. There is no false trigger happens although only O1 data are used for training. Our test results indicate that the ensemble learning algorithms can be used in real-time GW data analysis.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We report the discovery of CXOU J191100-595621 and CXOU J191012-595619, two galaxy clusters serendipitously detected in the direction of globular cluster NGC 6752, based on archival {\it Chandra} observations with a total exposure time of $\sim 344$ ks. The deep {\it Chandra} X-ray data enabled us to measure properties of both systems, which result in a redshift of $z=0.239\pm0.013$ and $z=0.375\pm0.016$, a temperature of $kT=3.32^{+0.57}_{-0.46}$ keV and $kT=3.71^{+1.18}_{-0.86}$ keV, an iron abundance of $Z_{\rm Fe}=0.64^{+0.34}_{-0.29}Z_{\rm Fe\odot}$ and $Z_{\rm Fe}=1.29^{+0.97}_{-0.65}Z_{\rm Fe\odot}$, and a rest-frame full band (0.5-7 keV) luminosity of $L_{\rm X}=9.2^{+1.2}_{-1.1}\times 10^{43} {\rm \, erg\, s^{-1}}$ and $L_{\rm X}=9.9^{+2.7}_{-2.2}\times 10^{43} {\rm \, erg\, s^{-1}}$ for CXOU J191100-595621 and CXOU J191012-595619, respectively. The temperature profile of CXOU J191100-595621 is found to decreases with decreasing radius, indicating a cool core in this cluster. The hydrostatic equilibrium estimation suggests the clusters are moderately weighted, with $M_{500}=(1.3\pm0.4)\times 10^{14}\, M_{\odot}$ and $M_{500}=(2.0\pm1.5)\times 10^{14}\, M_{\odot}$, respectively. We search for optical and radio counterparts of X-ray point sources in the clusters. Three active galactic nuclei are found, among which one is identified with a narrow-angle-tail radio galaxy, and one is found to associated with the brightest central galaxy (BCG) of CXOU J191100-595621.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Random sampling in high dimensions has successfully been applied to phenomena as diverse as nuclear resonances, neural networks and black hole evaporation. Here we revisit an elegant argument by the British physicist Dennis Sciama, which demonstrated that were our universe random, it would almost certainly have a negligible chance for life. Under plausible assumptions, we show that a random universe can masquerade as `intelligently designed,' with the fundamental constants instead appearing to be fined tuned to achieve the highest probability for life to occur. For our universe, this mechanism may only require there to be around a dozen currently unknown fundamental constants. More generally, this mechanism appears to be important for data science analysis on constrained sets. Finally, we consider wider applications.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Cassiopeia A (Cas A) supernova remnant shows strong radiation from radio to gamma-ray bands. The mechanism of gamma-ray radiation in Cas A and its possible contribution to PeV cosmic rays are still under debate. The X-ray imaging reveals an asymmetric profile of Cas A, suggesting the existence of a jet-like structure. In this work, we propose an asymmetrical model for Cas A, consisting of a fast moving jet-like structure and a slowly expanding isotropic shell. This model can account for the multi-wavelength spectra of Cas A, especially for the power-law hard X-ray spectrum from $\sim$ 60 to 220 keV. The GeV to TeV emission from Cas A should be contributed by both hadronic and leptonic processes. Moreover, the jet-like structure may produce a gamma-ray flux of $\sim 10^{-13}\rm erg\ cm^{-2}\ s^{-1}$ at $\sim 100$ TeV, to be examined by LHAASO and CTA.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Tidal disruption event (TDE) can launch an ultrafast outflow. If the black hole is surrounded by large amounts of clouds, outflow-cloud interaction will generate bow shocks, accelerate electrons and produce radio emission. Here we investigate the interaction between a non-relativistic outflow and clouds in active galaxies, which is manifested as outflow-BLR (broad line region) interaction, and can be extended to outflow-torus interaction. This process can generate considerable radio emission, which may account for the radio flares appearing a few months later after TDE outbursts. Benefitting from efficient energy conversion from outflow to shocks and the strong magnetic field, outflow-cloud interaction may play a non-negligible, or even dominating role in generating radio flares in a cloudy circumnuclear environment if the CNM density is no more than 100 times the Sgr A*-like one. In this case, the evolution of radio spectra can be used to directly constrain the properties of outflows.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The Mingantu Spectral Radioheliograph (MUSER), a new generation of solar dedicated radio imaging-spectroscopic telescope, has realized high-time, high-angular, and high-frequency resolution imaging of the sun over an ultra-broadband frequency range. Each pair of MUSER antennas measures the complex visibility in the aperture plane for each integration time and frequency channel. The corresponding radio image for each integration time and frequency channel is then obtained by inverse Fourier transformation of the visibility data. In general, the phase of the complex visibility is severely corrupted by instrumental and propagation effects. Therefore, robust calibration procedures are vital in order to obtain high-fidelity radio images. While there are many calibration techniques available -- e.g., using redundant baselines, observing standard cosmic sources, or fitting the solar disk -- to correct the visibility data for the above-mentioned phase errors, MUSER is configured with non-redundant baselines and the solar disk structure cannot always be exploited. Therefore it is desirable to develop alternative calibration methods in addition to these available techniques whenever appropriate for MUSER to obtain reliable radio images. In the case that a point-like calibration source containing an unknown position error, we have for the first time derived a mathematical model to describe the problem and proposed an optimization method to calibrate this unknown error by studying the offset of the positions of radio images over a certain period of the time interval. Simulation experiments and actual observational data analyses indicate that this method is valid and feasible. For MUSER's practical data the calibrated position errors are within the spatial angular resolution of the instrument. This calibration method can also be used in other situations for radio aperture synthesis observations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We revisit the possibility that Dark Matter is composed of stable scalar glueballs of a confining dark ${\rm SU}(3)$ gauge theory coupled only to gravity. The relic abundance of dark glueballs is studied for the first time in a thermal effective theory accounting for strong-coupling dynamics. An important ingredient of our analysis is the use of an effective potential for glueballs that is fitted by lattice simulations. We predict the relic abundance to be in the range $0.12\zeta_{T}^{-3}\Lambda/(137.9 {\rm eV}) \lesssim \Omega h^{2}\lesssim 0.12\zeta_{T}^{-3}\Lambda/(82.7 {\rm eV})$, with $\Lambda$ being the confinement scale, $\zeta_{T}$ the visible-to-dark sector temperature ratio and the uncertainty is coming from the fit to lattice data. This prediction is an order of magnitude smaller than the existing glueball abundance results in the literature. Our framework can be easily generalised to different gauge groups and modified cosmological histories paving the way towards consistent exploration of strongly-coupled dark sectors and their cosmological implications.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： When considered as orthogonal bases in distinct vector spaces, the unit vectors of polarization directions and the Laguerre-Gaussian modes of polarization amplitude are inseparable, constituting a so-called classical entangled light beam. Equating this classical entanglement to quantum entanglement necessary for computing purpose, we show that the parallelism featured in Shor's factoring algorithm is equivalent to the concurrent light-path propagation of an entangled beam or pulse train. A gedanken experiment is proposed for executing the key algorithmic steps of modular exponentiation and Fourier transform on a target integer $N$ using only classical manipulations on the amplitudes and polarization directions. The multiplicative order associated with the sought-after integer factors is identified through a four-hole diffraction interference from sources obtained from the entangled beam profile. The unique mapping from the fringe patterns to the computed order is demonstrated through simulations for the case $N=15$.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： Simultaneous wireless information and power transfer (SWIPT) is a remarkable technology to support both the data and the energy transfer in the era of Internet of Things (IoT). In this paper, we proposed a long-range optical wireless information and power transfer system utilizing retro-reflectors, a gain medium, a telescope internal modulator to form the resonant beam, achieving high-power and high-rate SWIPT. We adopt the transfer matrix, which can depict the beam modulated, resonator stability, transmission loss, and beam distribution. Then, we provide a model for energy harvesting and data receiving, which can evaluate the SWIPT performance. Numerical results illustrate that the proposed system can simultaneously supply 0$\sim$9 W electrical power and 18 bit/s/Hz spectral efficiency over 20 m distance.
分类： 物理学 >> 核物理学 提交时间： 2016-08-30
摘要： Flavor SU(3) symmetry is a powerful tool to analyze charmed baryon decays, however its applicability remains to be experimentally validated. Since there is not much data on Ξc decays, various exclusive Λc decays especially the ones into a neutron state are essential for the test of flavor symmetry. These decay modes are also helpful to investigate final state interactions in charmed baryon decays. In this work, we discuss the explicit roles of Λc decays into a neutron in testing the flavor symmetry and exploring final state interactions. The involved decay modes include semileptonic decays, two-body and three-body non-leptonic decays, but all of them have not been experimentally observed to date.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： As a dedicated solar radioheliograph, the MingantU SpEctral RadioHeliograph (MUSER) has a maximum baseline of more than 3000 meters and a frequency range of 400 MHz -- 15 GHz. According to the classical radio interferometry theory, the non-coplanar baseline effect (i.e., w-term effect) would be considered and calibrated for such a radio instrument. However, little previous literature made the qualitative or quantitative analyses on w-term effects of solar radioheliograph in-depth. This study proposes a complete quantitative analysis of w-term effects for the MUSER. After a brief introduction of the MUSER, we systematically investigate the baseline variations over a year and analyze the corresponding variations of w-term. We further studied the effects of the w-term in the imaging for the specified extended source, i.e., the Sun. We discussed the possible effects of the w-term, such as image distortion and so on. The simulated results show that the w-term is an essential and unavoidable issue for solar radio imaging with high spatial resolution.
分类： 物理学 >> 基本粒子与场物理学 提交时间： 2017-08-05
摘要： In the three-dimensional sl(N) Chern-Simons higher-spin theory, we prove that the conical surplus and the black hole solution are related by the S-transformation of the modulus of the boundary torus. Then applying the modular group on a given conical surplus solution, we generate a 'SL(2,Z)' family of smooth constant solutions. We then show how these solutions are mapped into one another by coordinate transformations that act non-trivially on the homology of the boundary torus. After deriving a thermodynamics that applies to all the solutions in the 'SL(2,Z)' family, we compute their entropies and free energies, and determine how the latter transform under the modular transformations. Summing over all the modular images of the conical surplus, we write down a (tree-level) modular invariant partition function.
分类： 天文学 >> 天文学 提交时间： 2024-02-28 合作期刊: 《Research in Astronomy and Astrophysics》
摘要： Using archival Fermi-LAT data with a time span of ∼12 yr, we study the population of Millisecond Pulsars (MSPs) in Globular Clusters (GlCs) and investigate their dependence on cluster dynamical evolution in the Milky Way. We show that the γ-ray luminosity (Lγ) and emissivity (i.e.,= Lγ/M, with M the cluster mass) are good indicators of the population and abundance of MSPs in GlCs, and they are highly dependent on the dynamical evolution history of the host clusters. Specifically speaking, the dynamically older GlCs with more compact structures are more likely to have larger Lγ and , and these trends can be summarized as strong correlations with cluster stellar encounter rate Γ and the specific encounter rate (Λ = Γ/M), with Lγ ∝ Γ0.70±0.11 and ∝ Λ0.73±0.13 for dynamically normal GlCs. However, as GlCs evolve into deep core collapse, these trends are found to be reversed, implying that strong encounters may have lead to the disruption of Low-Mass X-ray Binaries and ejection of MSPs from core-collapsed systems. Besides, the GlCs are found to exhibit larger with increasing stellar mass function slope (∝ 10(0.57±0.1)α), decreasing tidal radius () and distances from the Galactic Center (GC, ). These correlations indicate that, as GlCs losing kinetic energy and spiral in toward the GC, tidal stripping and mass segregation have a preference in leading to the loss of normal stars from GlCs, while MSPs are more likely to concentrate to cluster center and be deposited into the GC. Moreover, we gauge of GlCs is ∼10–1000 times larger than the Galactic bulge, the latter is thought to reside thousands of unresolved MSPs and may be responsible for the GC γ-ray excess, which supports that GlCs are generous contributors to the population of MSPs in the GC.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We conduct a detailed analysis of an M1.3 limb flare occurring on 2017 July 3, which have the X-ray observations recorded by multiple hard X-ray telescopes, including Hard X-ray Modulation Telescope (Insight-HXMT), Ramaty High Energy Solar Spectroscopic Imager (RHESSI), and The Fermi Gamma-ray Space Telescope (FERMI). Joint analysis has also used the EUV imaging data from the Atmospheric Imaging Assembly (AIA) aboard the Solar Dynamic Observatory. The hard X-ray spectral and imaging evolution suggest a lower corona source, and the non-thermal broken power law distribution has a rather low break energy $\sim$ 15 keV. The EUV imaging shows a rather stable plasma configuration before the hard X-ray peak phase, and accompanied by a filament eruption during the hard X-ray flare peak phase. Hard X-ray image reconstruction from RHESSI data only shows one foot point source. We also determined the DEM for the peak phase by SDO/AIA data. The integrated EM beyond 10 MK at foot point onset after the peak phase, while the $>$ 10 MK source around reconnection site began to fade. The evolution of EM and hard X-ray source supports lower corona plasma heating after non-thermal energy dissipation. The combination of hard X-ray spectra and images during the limb flare provides the understanding on the interchange of non-thermal and thermal energies, and relation between lower corona heating and the upper corona instability.
分类： 光学 >> 量子光学 提交时间： 2023-02-19
摘要： The synthetic dimension, a research topic of both fundamental significance and practical applications, is attracting increasing attention in recent years. In this paper, we propose a theoretical framework to construct arbitrary synthetic dimensions, or N-boson synthetic lattices, using multiple bosons on one-dimensional lattices. We show that a one-dimensional lattice hosting N indistinguishable bosons can be mapped to a single boson on a N-dimensional lattice with high symmetry. Band structure analyses on this N-dimensional lattice can then be mathematically performed to predict the existence of exotic eigenstates and the motion of N-boson wavepackets. As illustrative examples, we demonstrate the edge states in two-boson Su-Schrieffer-Heeger synthetic lattices without interactions, interface states in two-boson Su-Schrieffer-Heeger synthetic lattices with interactions, and weakly-bound triplon states in three-boson tight-binding synthetic lattices with interactions. The interface states and weakly-bound triplon states have not been thoroughly understood in previous literatures. Our proposed theoretical framework hence provides a novel perspective to explore the multi-boson dynamics on lattices with boson-boson interactions, and opens up a future avenue in the fields of multi-boson manipulation in quantum engineering.
分类： 物理学 >> 核物理学 提交时间： 2016-09-13
摘要： We study S-wave resonance contributions to the B0(s)→J/ψπ+π− and Bs→π+π−ℓ+ℓ− decays in the perturbative QCD (PQCD) framework by introducing two-hadron distribution amplitudes for final states. The Breit-Wigner formula for the f0(500), f0(1500) and f0(1790) resonances and the Flatt\'e model for the f0(980)resonance are adopted to parameterize the time-like scalar form factors in the two-pion distribution amplitudes, which include both resonant and nonresonant contributions. The resultant branching fraction and differential branching fraction in the pion-pair invariant mass for each resonance channel are consistent with experimental data. The determined S-wave two-pion distribution amplitudes, containing the information of both resonant and nonresonant rescattering phases, can be employed to predict direct CP asymmetries of other three-body hadronic B meson decays in various localized regions of two-pion phase space.
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