查看更多>>摘要：A warm corona has been widely proposed to explain the soft excess(SE)in X-ray above the 2-10 keV power law extrapolation in Active Galactic Nuclei(AGNs).In actual spectral fittings,the warm coronal seed photon temperature(Ts)is usually assumed to be far away from the soft X-ray,but kTs can reach close to 0.1 keV in the standard accretion disk model.In this study,we used Monte Carlo simulations to obtain radiation spectra from a slab-like warm corona and fitted the spectra using the spherical-geometry-based routine THCOMP or a thermal component.Our findings reveal that high Ts can influence the fitting results.A moderately high kTs(around 0.03 keV)can result in an apparent low-temperature and flat SE,while an extremely high kTs(around 0.07 keV)can even produce an unobserved blackbody-like SE.Our conclusions indicate that,for spectral fittings of the warm coronal radiation(SE in AGNs),kTs should be treated as a free parameter with an upper limit,and an accurate coronal geometry is necessary when kTs＞0.01 keV.
查看更多>>摘要：For real-time processing of ultra-wide bandwidth low-frequency pulsar baseband data,we designed and implemented an ultra-wide bandwidth low-frequency pulsar data processing pipeline(UWLPIPE)based on the shared ringbuffer and GPU parallel technology.UWLPIPE runs on the GPU cluster and can simultaneously receive multiple 128 MHz dual-polarization VDIF data packets preprocessed by the front-end FPGA.After aligning the dual-polarization data,multiple 128M subband data are packaged into PSRDADA baseband data or multi-channel coherent dispersion filterbank data,and multiple subband filterbank data can be spliced into wideband data after time alignment.We used the Nanshan 26 m radio telescope with the L-band receiver at 964～1732 MHz to observe multiple pulsars.Finally,we processed the data using DSPSR software,and the results showed that each subband could correctly fold out the pulse profile,and the wideband pulse profile accumulated by multiple subbands could be correctly aligned.
查看更多>>摘要：The China Space Station Telescope(CSST)is a telescope with 2 m diameter,obtaining images with high quality through wide-field observations.In its first observation cycle,to capture time-domain observation data,the CSST is proposed to observe the Galactic halo across different epochs.These data have significant potential for the study of properties of stars and exoplanets.However,the density of stars in the Galactic center is high,and it is a well-known challenge to perform astrometry and photometry in such a dense star field.This paper presents a deep learning-based framework designed to process dense star field images obtained by the CSST,which includes photometry,astrometry,and classifications of targets according to their light curve periods.With simulated CSST observation data,we demonstrate that this deep learning framework achieves photometry accuracy of 2％and astrometry accuracy of 0.03 pixel for stars with moderate brightness mag=24(i band),surpassing results obtained by traditional methods.Additionally,the deep learning based light curve classification algorithm could pick up celestial targets whose magnitude variations are 1.7 times larger than magnitude variations brought by Poisson photon noise.We anticipate that our framework could be effectively used to process dense star field images obtained by the CSST.
查看更多>>摘要：After launching a jet,outflows of magnetar were used to account for the achromatic plateau of afterglow and the early X-ray flux plateau known as"internal plateau".The lack of detecting magnetic dipole emission together with the energy injection feature in a single observation poses confusion until the long gamma-ray burst(GRB)210610B is detected.GRB 210610B is presented with an optical bump following an early X-ray plateau during the afterglow phase.The plateau followed by a steep decline flux overlays in the steadily decaying X-ray flux with index αx,l～2.06,indicating an internal origin and that can be fitted by the spin-down luminosity law with the initial plateau luminosity log10Lx～48.29 erg s-1 and the characteristic spin-down timescale T～2818 s.A subsequent bump begins at～4000 s in the R band with a rising index αR,1～-0.30 and peaks at～14125 s,after which a decay index αR,2～0.87 and finally transiting to a steep decay with αR,3～1.77 achieve the closure relation of the external shock for the normal decay phase as well as the magnetar spin-down energy injection phase,provided that the average value of the photon index Γγ=1.80 derived from the spectral energy distributions(SEDs)between the X-ray and optical afterglow.The closure relation also works for the late X-ray flux.Akin to the traditional picture of GRB,the outflow powers the early X-ray plateau by dissipating energy internally and collides with the leading decelerating blast burst as time goes on,which could interpret the exotic feature of GRB 210610B.We carry out a Markov Chain Monte Carlo simulation and obtain a set of best parameters:εB(≌)4.7 × 10-5,εe(≌)0.15,EK,iso(≌)4.6 × 1053erg,T0(≌)832,A*(≌)0.10,Linj,0(≌)3.55 × 1050erg s-1.The artificial light curve can fit the afterglow data well.After that,we estimated the average Lorentz factor and the X-ray radiation efficiency of the later ejecta are 35％and 0.13％,respectively.
查看更多>>摘要：In star formation regions,the complex organic molecules(COMs)that contain peptide bonds(-NH-C(=O)-)play a major role in the metabolic process because-NH-C(=O)-is connected to amino acids(R-CHNH2-COOH).Over the past few decades,many COMs containing peptide-like bonds have been detected in hot molecular cores(HMCs),hot corinos,and cold molecular clouds,however,their prebiotic chemistry is poorly understood.We present the first detection of the rotational emission lines of formamide(NH2CHO)and isocyanic acid(HNCO),which contain peptide-like bonds toward the chemically rich HMC G358.93-0.03 MM1,using high-resolution and high-sensitivity Atacama Large Millimeter/submillimeter Array bands 6 and 7.We estimate that the column densities of NH2CHO and HNCO toward G358.93-0.03 MM1 are(2.80±0.29)× 1015cm-2 and(1.80±0.42)× 1016cm-2 with excitation temperatures of 165±21K and 170±32K,respectively.The fractional abundances of NH2CHO and HNCO toward G358.93-0.03 MM1 are(9.03±1.44)× 10-10 and(5.80±2.09)× 10-9.We compare the estimated abundances of NH2CHO and HNCO with the existing three-phase warm-up chemical model abundance values and notice that the observed and modeled abundances are very close.We conclude that NH2CHO is produced by the reaction of NH2 and H2CO in the gas phase toward G358.93-0.03 MM1.Likewise,HNCO is produced on the surface of grains by the reaction of NH and CO toward G358.93-0.03 MM1.We also find that NH2CHO and HNCO are chemically linked toward G358.93-0.03 MM1.
查看更多>>摘要：The polar magnetic fields of the Sun play an important role in governing solar activity and powering fast solar wind.However,because our view of the Sun is limited in the ecliptic plane,the polar regions remain largely uncharted.Using the high spatial resolution and polarimetric precision vector magnetograms observed by Hinode from 2012 to 2021,we investigate the long-term variation of the magnetic fields in polar caps at different latitudes.The Hinode magnetic measurements show that the polarity reversal processes in the north and south polar caps are non-simultaneous.The variation of the averaged radial magnetic flux density reveals that,in each polar cap,the polarity reversal is completed successively from the 70° latitude to the pole,reflecting a poleward magnetic flux migration therein.These results clarify the polar magnetic polarity reversal process at different latitudes.
查看更多>>摘要：In this paper,we analyze the spectral energy distributions of 17 powerful(with a spin-down luminosity greater than 1035 erg s-1)young(with an age less than 15,000 yr)pulsar wind nebulae(PWNe)using a simple time-independent one-zone emission model.Our aim is to investigate correlations between model parameters and the ages of the corresponding PWNe,thereby revealing the evolution of high-energy electron distributions within PWNe.Our findings are as follows:(1)The electron distributions in PWNe can be characterized by a double power-law with a super-exponential cutoff.(2)As PWNe evolve,the high-energy end of the electron distribution spectrum becomes harder with the index decreasing from approximately 3.5 to 2.5,while the low-energy end spectrum index remains constant near 1.5.(3)There is no apparent correlation between the break energy or cutoff energy and the age of PWNe.(4)The average magnetic field within PWNe decreases with age,leading to a positive correlation between the energy loss timescale of electrons at the break energy or the high-energy cutoff,and the age of the PWN.(5)The total electron energy within PWNe remains constant near 2 × 1048 erg,while the total magnetic energy decreases with age.
查看更多>>摘要：Sulfur chemistry in the formation process of low-mass stars and planets remains poorly understood.The protoplanetary disks are the birthplace of planets and its distinctive environment provides an intriguing platform for investigating models of sulfur chemistry.We analyzed the Atacama Large Millimeter/submillimeter Array observations of CS 7-6 transitions in the HD 163296 disk and performed astrochemical modeling to explore its sulfur chemistry.We simulated the distribution of sulfur-containing molecules and compared it with observationally deduced fractional column densities.We have found that the simulated column density of CS is consistent with the observationally deduced fractional column densities,while the simulated column density of C2S is lower than the observationally deduced upper limits on column densities.This results indicate that we have a good understanding of the chemical properties of CS and C2S in the disk.We also investigated the influence of the C/O ratio on sulfur-containing molecules and found that the column densities of SO,SO2,and H2S near the central star are dependent on the C/O ratio.Additionally,we found that the N[CS]/N[SO]ratio can serve as a promising indicator of the disk's C/O ratio in HD 163296.Overall,the disk of HD 163296 provides a favorable environment for the detection of sulfur-containing molecules.
查看更多>>摘要：Active reflectors are often used to compensate the surface distortion caused by environmental factors that degrade the electromagnetic performance of large high-frequency reflector antennas.This is crucial for maintaining high gain operation in antennas.A distortion compensation method for the active reflector of a large dual-reflector antenna is proposed.A relationship is established between the surface deformation and the optical path difference for the primary reflector by geometric optics.Subsequently,employing finite element analysis,a polynomial fitting approach is used to describe the impact of adjusting points on the reflector surface based on the coordinates of each node.By standardizing the positions of various panels on the reflector,the fitting ns can be applied to the reflector panels of similar shapes.Then,based on the distribution characteristics of the primary reflector panels,the adjustment equation for the actuators is derived by the influence matrix method.It can be used to determine the adjustment amount of actuators to reduce the rms of the optical path difference.And,the least squares method is employed to resolve the matrix equation.The example of a 110 m aperture dual-reflector antenna is carried out by finite element analysis and the proposed method.The results show that the optical path difference is reduced significantly at various elevation cases,which indicates that the proposed method is effective.
查看更多>>摘要：Superthin galaxies are observed to have stellar disks with extremely small minor-to-major axis ratios.In this work,we investigate the formation of superthin galaxies in the TNG100 simulation.We trace the merger history and investigate the evolution of galaxy properties of a selected sample of superthin galaxies and a control sample of galaxies that share the same joint probability distribution in the stellar-mass and color diagram.Through making comparisons between the two galaxy samples,we find that present-day superthin galaxies had similar morphologies as the control sample counterparts at higher redshifts,but have developed extended flat"superthin"morphologies since z～1.During this latter evolution stage,superthin galaxies undergo an overwhelmingly higher frequency of prograde mergers(with orbit-spin angle θorb≤40°).Accordingly the spins of their dark matter halos have grown significantly and become noticeably higher than those of their normal disk counterparts.This further results in the buildup of their stellar disks at larger distances much beyond the regimes of normal disk galaxies.We also discuss the formation scenario of those superthin galaxies that live in larger dark matter halos as satellite galaxies therein.
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