In order to search for intensity fluctuations on the HCN（1-0） and HCO＋（1-0） line pro- files, which could arise due to possible small-scale inhomogeneous structure, long-term observations of high-mass star-forming...In order to search for intensity fluctuations on the HCN（1-0） and HCO＋（1-0） line pro- files, which could arise due to possible small-scale inhomogeneous structure, long-term observations of high-mass star-forming cores S140 and S199 were carried out. The data were processed by the Fourier filtering method. Line temperature fluctuations that exceed the noise level were detected. Assuming the cores consist of a large number of randomly moving small thermal fragments, the total number of frag- ments is - 4 × 106 for the region with linear size - 0.1 pc in S140 and - 106 for the region with linear size - 0.3 pc in S 199. Physical parameters of fragments in S 140 were obtained from detailed modeling of the HCN emission in the framework of the clumpy cloud model.展开更多
Due to the low spatial resolution of images taken from the Chang＇e-1 （CE-I） orbiter, the details of the lunar surface are blurred and lost. Considering the limited spatial resolution of image data obtained by a CCD...Due to the low spatial resolution of images taken from the Chang＇e-1 （CE-I） orbiter, the details of the lunar surface are blurred and lost. Considering the limited spatial resolution of image data obtained by a CCD camera on CE-1, an example-based super-resolution （SR） algorithm is employed to obtain high- resolution （HR） images. SR reconstruction is important for the application of image data to increase the resolution of images. In this article, a novel example-based algorithm is proposed to implement SR reconstruction by single-image analysis, and the computational cost is reduced compared to other example-based SR methods. The results show that this method can enhance the resolution of images using SR and recover detailed information about the lunar surface. Thus it can be used for surveying HR terrain and geological features. Moreover, the algorithm is significant for the HR processing of remotely sensed images obtained by other imaging systems.展开更多
We performed detailed time-resolved spectroscopy of bright tong gamma- ray bursts （GRBs） which show significant GeV emissions （GRB 080916C, GRB 090902B and GRB 090926A）. In addition to the standard Band model, we ...We performed detailed time-resolved spectroscopy of bright tong gamma- ray bursts （GRBs） which show significant GeV emissions （GRB 080916C, GRB 090902B and GRB 090926A）. In addition to the standard Band model, we also use a model consisting of a black body and a power law to fit the spectra. We find that for the latter model there are indications of an additional soft component in the spectra. While previous studies have shown that such models are required for GRB 090902B, here we find that a composite spectral model consisting of two blackbodies and a power law adequately fits the data of all the three bright GRBs. We investigate the evolution of the spectral parameters and find several interesting features that appear in all three GRBs, like （a） temperatures of the blackbodies are strongly correlated with each other, （b） fluxes in the black body components are strongly correlated with each other, （c） the temperatures of the black body trace the profile of the individual pulses of the GRBs, and （d） the characteristics of power law components like the spectral index and the delayed onset bear a close similarity to the emission characteristics in the GeV regions. We discuss the implications of these results and the possibility of identifying the radiation mechanisms during the prompt emission of GRBs.展开更多
We investigate the wavelet transform of yearly mean relative sunspot number series from 1700 to 2002. The curve of the global wavelet power spectrum peaks at 11-yr, 53-yr and 101-yr periods. The evolution of the ampli...We investigate the wavelet transform of yearly mean relative sunspot number series from 1700 to 2002. The curve of the global wavelet power spectrum peaks at 11-yr, 53-yr and 101-yr periods. The evolution of the amplitudes of the three periods is studied. The results show that around 1750 and 1800, the amplitude of the 53-yr period was much higher than that of the the 11-yr period, that the ca. 53-yr period was apparent only for the interval from 1725 to 1850, and was very low after 1850, that around 1750, 1800 and 1900, the amplitude of the 101-yr period was higher than that of the 11-yr period and that, from 1940 to 2000, the 11-yr period greatly dominates over the other two periods.展开更多
The Large sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) medium-resolution spectral survey of Galactic Nebulae(MRS-N) has conducted for more than three years since 2018 September and observed more than190...The Large sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) medium-resolution spectral survey of Galactic Nebulae(MRS-N) has conducted for more than three years since 2018 September and observed more than190 thousand nebular spectra and 20 thousand stellar spectra.However,there is not yet a data processing pipeline for nebular spectra.To significantly improve the accuracy of nebulae classification and their physical parameters,we developed the MRS-N Pipeline.This article presented in detail each data processing step of the MRS-N Pipeline,such as removing cosmic rays,merging single exposure,fitting sky light emission lines,wavelength recalibration,subtracting skylight,measuring nebular parameters,creating catalogs and packing spectra.Finally,a description of the data products,including nebular spectra files and parameter catalogs,is provided.展开更多
The nature of random errors in any data set is Gaussian, which is a well established fact according to the Central Limit Theorem. Supernovae type Ia data have played a crucial role in major discoveries in cosmology. U...The nature of random errors in any data set is Gaussian, which is a well established fact according to the Central Limit Theorem. Supernovae type Ia data have played a crucial role in major discoveries in cosmology. Unlike in laboratory experiments, astronomical measurements cannot be performed in controlled situations. Thus, errors in astronomical data can be more severe in terms of systematics and non-Gaussianity compared to those of laboratory experiments. In this paper, we use the Kolmogorov-Smiruov statistic to test non-Gaussianity in high-z supernovae data. We apply this statistic to four data sets, i.e., Gold data （2004）, Gold data （2007）, the Union2 catalog and the Union2.1 data set for our analysis. Our results show that in all four data sets the errors are consistent with a Gaussian distribution.展开更多
In this work,we present a systematic comp arison of single-and multiple-sc attering models for dust-scattered starlight across the UV sky and attempt to derive a simulation model of multiple-scattered radiation using ...In this work,we present a systematic comp arison of single-and multiple-sc attering models for dust-scattered starlight across the UV sky and attempt to derive a simulation model of multiple-scattered radiation using the single-scattered radiation.Our new simulated multiple-scattering model uses a critical angle(θ_(c)),which is dependent on optical depth(τ),albedo(a),and phase function asymmetry(g),to replace the computationally intensive full Monte Carlo treatment.We find that multiple-scattering becomes increasingly important in almost all optical depths,depending on the scattering geometry.UV-bright stars show a peak scattering intensity near the stellar disk,dropping by an order of magnitude within 10°-15°and merging with the background at 40°-50°,whereas fainter or more distant stars require larger angular separations to reach the same relative reduction.We introduce a functional form,I_(θ)=I_(0)(1-tanh(SP×θ)),to describe the radial decrease in scattered intensity,with the slope parameter declining systematically for more distant stars.Depending on a star's position,multiplescattered fluxes can exceed single-scattered fluxes by up to 200%,and both converge at a critical angle,θ_(c),which depends logarithmically on stellar distance and is governed byτ,a,and g.Notably,θ_(c)remains independent of Galactic longitude or latitude,underscoring the robust,geometry-driven nature of the scattering process.展开更多
This study numerically investigates the formation of high-velocity molecular clouds(HVMCs)in the Galactic Center(GC)based on the X-ray emission analysis.We employ three-dimensional magnetohydrodynamic simulations to e...This study numerically investigates the formation of high-velocity molecular clouds(HVMCs)in the Galactic Center(GC)based on the X-ray emission analysis.We employ three-dimensional magnetohydrodynamic simulations to explore the propagation and acceleration of HVMCs with starburst-driven winds,considering vertical,horizontal,and no magnetic field scenarios.Our results reveal that the envelope gas(with a typical T~10~8 K and density~10^(-2)cm^(-3))of molecular clouds(MCs)as a result of the shock interaction is responsible for X-ray emission.Additionally,some clear boundary exists between the interstellar medium(ISM),envelope gas and MCs,and the envelope gas protects the MCs in the heated environment of the shock wave.In theory,it is challenging to distinguish between the envelope gas,MCs and ISM in terms of X-ray emission.Our simulations suggest that the envelope gas has a significant impact on the survival and emission characteristics of MCs,providing insights into the complex interactions from the supernova feedback mechanisms in the GC.展开更多
Determining accurate pulsar timing model parameters is essential for establishing TT(PT),a realization of Terrestrial Time(TT)based on a pulsar timescale(PT).This study discusses the impact of different data spans on ...Determining accurate pulsar timing model parameters is essential for establishing TT(PT),a realization of Terrestrial Time(TT)based on a pulsar timescale(PT).This study discusses the impact of different data spans on the accuracy of pulsar timing model parameters when determining pulsar timing model parameters.Using observations of PSR J0437-4715,J1909-3744,J1713+0747,and J1744-1134 from the second data release of the International Pulsar Timing Array(IPTA II,Version A),we compare the accuracy of the timing model parameters determined by these observations with different data spans.The results show for PSR J0437-4715,J1713+0747,and J1909-3744,the amplitude fluctuations of rotational frequency remain within 10^(−15),10^(−14),and 10^(−14) Hz,respectively,when the data spans for determining pulsar timing model parameters exceed 13,14,and 6 yr.Additionally,the one-year accuracy of TT(PT)is crucial for its application in timekeeping.By comparing the frequency deviations of TT(PT)relative to TT(BIPM)under both ideal(k_(r))and actual(k_(p))conditions across different data spans,we find that when the data span reaches the duration above,the accuracy of TT(PT)surpasses that of TT(TAI)under ideal conditions,slightly inferior under actual conditions.This suggests with improved observational technologies,the accuracy of TT(PT)can be further enhanced.展开更多
With the development of large-scale spectral surveys, fiber positioning technology has been developing rapidly. Because of the performance advantages of a four-quadrant（4Q） detector, a fiber positioning and real-tim...With the development of large-scale spectral surveys, fiber positioning technology has been developing rapidly. Because of the performance advantages of a four-quadrant（4Q） detector, a fiber positioning and real-time monitoring system based on the 4Q detector is proposed. The detection accuracy of this system is directly determined by the precision of the center of the spot. A Gaussian fitting algorithm based on the 4Q detector is studied and applied in the fiber positioning process to improve the calculated accuracy of the spot center. The relationship between the center position of the incident spot and the detector output signal is deduced. An experimental platform is built to complete the simulated experiment. Then we use the Gaussian fitting method to process experimental data, compare the fitting value with the theoretical one and calculate the corresponding error.展开更多
The DArk Matter Particle Explorer（DAMPE）,also known as Wukong in China,which was launched on 2015 December 17,is a new high energy cosmic ray and γ-ray satellite-borne observatory.One of the main scientific goals o...The DArk Matter Particle Explorer（DAMPE）,also known as Wukong in China,which was launched on 2015 December 17,is a new high energy cosmic ray and γ-ray satellite-borne observatory.One of the main scientific goals of DAMPE is to observe Ge V-Te V high energy γ-rays with accurate energy,angular and time resolution,to indirectly search for dark matter particles and for the study of high energy astrophysics. Due to the comparatively higher fluxes of charged cosmic rays with respect to γ-rays,it is challenging to identify γ-rays with sufficiently high efficiency,minimizing the amount of charged cosmic ray contamination. In this work we present a method to identify γ-rays in DAMPE data based on Monte Carlo simulations,using the powerful electromagnetic/hadronic shower discrimination provided by the calorimeter and the veto detection of charged particles provided by the plastic scintillation detector. Monte Carlo simulations show that after this selection the number of electrons and protons that contaminate the selected γ-ray events at～10 Ge V amounts to less than 1% of the selected sample.Finally,we use flight data to verify the effectiveness of the method by highlighting known γ-ray sources in the sky and by reconstructing preliminary light curves of the Geminga pulsar.展开更多
Using 64 ms count data of long gamma-ray bursts （T90 〉 2.6 s）, we analyze the quantity named relative spectral lag （RSL）, T31/FWHM（1）. We investigated in detail all the correlations between the RSL and other pa...Using 64 ms count data of long gamma-ray bursts （T90 〉 2.6 s）, we analyze the quantity named relative spectral lag （RSL）, T31/FWHM（1）. We investigated in detail all the correlations between the RSL and other parameters for a sample of nine long bursts, using the general cross-correlation technique that includes the lag between two different energy bands. We conclude that the distribution of RSLs is normal and has a mean value of 0.1; that the RSLs are weakly correlated with the FWHM, the asymmetry, peak flux （Fp）, peak energy （Ep） and spectral indexes （α and β）, while they are uncorrelated with τ31, the hardness- ratio （HR31） and the peak time （tm）. Our important discovery is that redshift （z） and peak luminosity （Lp） are strongly correlated with the RSL, which can be measured easily and directly, making the RSL a good redshift and peak luminosity indicator.展开更多
An accurate determination of the landing trajectory of Chang＇e-3 （CE-3） is significant for verifying orbital control strategy, optimizing orbital planning, accu- rately determining the landing site of CE-3 and anal...An accurate determination of the landing trajectory of Chang＇e-3 （CE-3） is significant for verifying orbital control strategy, optimizing orbital planning, accu- rately determining the landing site of CE-3 and analyzing the geological background of the landing site. Due to complexities involved in the landing process, there are some differences between the planned trajectory and the actual trajectory of CE-3. The land- ing camera on CE-3 recorded a sequence of the landing process with a frequency of 10 frames per second. These images recorded by the landing camera and high-resolution images of the lunar surface are utilized to calculate the position of the probe, so as to reconstruct its precise trajectory. This paper proposes using the method of trajectory reconstruction by Single Image Space Resection to make a detailed study of the hov- ering stage at a height of 100 m above the lunar surface. Analysis of the data shows that the closer CE-3 came to the lunar surface, the higher the spatial resolution of im- ages that were acquired became, and the more accurately the horizontal and vertical position of CE-3 could be determined. The horizontal and vertical accuracies were 7.09 m and 4.27 m respectively during the hovering stage at a height of 100.02 m. The reconstructed trajectory can reflect the change in CE-3＇s position during the powered descent process. A slight movement in CE-3 during the hovering stage is also clearly demonstrated. These results will provide a basis for analysis of orbit control strategy, and it will be conducive to adjustment and optimization of orbit control strategy in follow-up missions.展开更多
With the continuous development of urbanization in China,the country’s growing population brings great challenges to urban development.By mastering the refined population spatial distribution in administrative units,...With the continuous development of urbanization in China,the country’s growing population brings great challenges to urban development.By mastering the refined population spatial distribution in administrative units,the quantity and agglomeration of population distribution can be estimated and visualized.It will provide a basis for a more rational urban planning.This paper takes Beijing as the research area and uses a new Luojia1-01 nighttime light image with high resolution,land use type data,Points of Interest(POI)data,and other data to construct the population spatial index system,establishing the index weight based on the principal component analysis.The comprehensive weight value of population distribution in the study area was then used to calculate the street population distribution of Beijing in 2018.Then the population spatial distribution was visualize using GIS technology.After accuracy assessments by comparing the result with the WorldPop data,the accuracy has reached 0.74.The proposed method was validated as a qualified method to generate population spatial maps.By contrast of local areas,Luojia 1-01 data is more suitable for population distribution estimation than the NPP/VIIRS(Net Primary Productivity/Visible infrared Imaging Radiometer)nighttime light data.More geospatial big data and mathematical models can be combined to create more accurate population maps in the future.展开更多
Forbush decrease(FD),discovered by Scott E.Forbush about 80 years ago,is referred to as the non-repetitive short-term depression in Galactic cosmic ray(GCR)flux,presumed to be associated with large-scale perturbations...Forbush decrease(FD),discovered by Scott E.Forbush about 80 years ago,is referred to as the non-repetitive short-term depression in Galactic cosmic ray(GCR)flux,presumed to be associated with large-scale perturbations in solar wind and interplanetary magnetic field(IMF).It is the most spectacular variability in the GCR intensity which appears to be the compass for investigators seeking solar-terrestrial relationships.The method of selection and validation of FD events is very important to cosmic ray(CR)scientists.We have deployed new computer software to determine the amplitude and timing of FDs from daily-averaged CR data at Oulu Neutron Monitor station.The code selected 230 FDs between 1998 and 2002.In an attempt to validate the new FD automated catalog,the relationship between the amplitude of FDs,and IMF,solar wind speed(SWS)and geomagnetic storm indices(Dst,kp,ap)is tested here.A two-dimensional regression analysis indicates significant linear relationship between large FDs(CR(%)≤-3)and solar wind data and geomagnetic storm indices in the present sample.The implications of the relationship among these parameters are discussed.展开更多
An unusual timing and spectral state of a black hole microquasar XTE J1550- 564 observed with RXTE is analyzed. Millisecond variabilities are found, which are significantly shorter than the minimum possible time scale...An unusual timing and spectral state of a black hole microquasar XTE J1550- 564 observed with RXTE is analyzed. Millisecond variabilities are found, which are significantly shorter than the minimum possible time scale in the light curves of black hole binaries, as suggested by Sunyaev ＆ Revnivtsev （2000）. The X-ray spectral fitting result indicates that there is an unusual soft component in the spectrum, which may be responsible for the millisecond variabilities. The millisecond variabilities as well as the unusual soft spectral component should be produced from some small, but independent active regions in the accretion disk.展开更多
We present photometric observations in Sloan filters g′, i′of the eclipsing W UMa stars USNOA2.0 1350-17365531, V471 Cas, V479 Lac and V560 Lac. The sinusoidal-like O-C diagram of V471 Cas indicates the presence of ...We present photometric observations in Sloan filters g′, i′of the eclipsing W UMa stars USNOA2.0 1350-17365531, V471 Cas, V479 Lac and V560 Lac. The sinusoidal-like O-C diagram of V471 Cas indicates the presence of a third body with mass 0.12 M_⊙(a red dwarf) at distance 897 R_⊙. The O-C diagram of V479 Lac reveals a period decrease of d P/dt =-1.69 × 10-6d yr-1. The results of the light curve solutions are:(i) the targets are overcontact binaries with small fill-out factors;(ii) their components are F–K stars, comparable in size, whose temperature differences are below 80 K;(iii) all targets undergo partial eclipses and to limit the possible mass ratios we carried out two-step q-search analysis. The target global parameters(luminosities, radii, masses) were obtained on the basis of their Gaia distances and the results of our light curve solutions. The obtained total mass of V560 Lac turns out to be smaller than the lower mass limit for presently known W UMa binaries of 1.0-1.2 M_⊙, i.e. this target is a peculiar overcontact system.展开更多
基金support of the RFBR grants(projects 15–02–06098,16–02–00761 and18–02–00660)support of the Russian Science Foundation grant(project 17–12–01256)
文摘In order to search for intensity fluctuations on the HCN（1-0） and HCO＋（1-0） line pro- files, which could arise due to possible small-scale inhomogeneous structure, long-term observations of high-mass star-forming cores S140 and S199 were carried out. The data were processed by the Fourier filtering method. Line temperature fluctuations that exceed the noise level were detected. Assuming the cores consist of a large number of randomly moving small thermal fragments, the total number of frag- ments is - 4 × 106 for the region with linear size - 0.1 pc in S140 and - 106 for the region with linear size - 0.3 pc in S 199. Physical parameters of fragments in S 140 were obtained from detailed modeling of the HCN emission in the framework of the clumpy cloud model.
基金funded by the National Natural Science Foundation of China (Grant No. 51575388)
文摘Due to the low spatial resolution of images taken from the Chang＇e-1 （CE-I） orbiter, the details of the lunar surface are blurred and lost. Considering the limited spatial resolution of image data obtained by a CCD camera on CE-1, an example-based super-resolution （SR） algorithm is employed to obtain high- resolution （HR） images. SR reconstruction is important for the application of image data to increase the resolution of images. In this article, a novel example-based algorithm is proposed to implement SR reconstruction by single-image analysis, and the computational cost is reduced compared to other example-based SR methods. The results show that this method can enhance the resolution of images using SR and recover detailed information about the lunar surface. Thus it can be used for surveying HR terrain and geological features. Moreover, the algorithm is significant for the HR processing of remotely sensed images obtained by other imaging systems.
文摘We performed detailed time-resolved spectroscopy of bright tong gamma- ray bursts （GRBs） which show significant GeV emissions （GRB 080916C, GRB 090902B and GRB 090926A）. In addition to the standard Band model, we also use a model consisting of a black body and a power law to fit the spectra. We find that for the latter model there are indications of an additional soft component in the spectra. While previous studies have shown that such models are required for GRB 090902B, here we find that a composite spectral model consisting of two blackbodies and a power law adequately fits the data of all the three bright GRBs. We investigate the evolution of the spectral parameters and find several interesting features that appear in all three GRBs, like （a） temperatures of the blackbodies are strongly correlated with each other, （b） fluxes in the black body components are strongly correlated with each other, （c） the temperatures of the black body trace the profile of the individual pulses of the GRBs, and （d） the characteristics of power law components like the spectral index and the delayed onset bear a close similarity to the emission characteristics in the GeV regions. We discuss the implications of these results and the possibility of identifying the radiation mechanisms during the prompt emission of GRBs.
基金Supported by the National Natural Science Foundation of China
文摘We investigate the wavelet transform of yearly mean relative sunspot number series from 1700 to 2002. The curve of the global wavelet power spectrum peaks at 11-yr, 53-yr and 101-yr periods. The evolution of the amplitudes of the three periods is studied. The results show that around 1750 and 1800, the amplitude of the 53-yr period was much higher than that of the the 11-yr period, that the ca. 53-yr period was apparent only for the interval from 1725 to 1850, and was very low after 1850, that around 1750, 1800 and 1900, the amplitude of the 101-yr period was higher than that of the 11-yr period and that, from 1940 to 2000, the 11-yr period greatly dominates over the other two periods.
基金supported by the National Natural Science Foundation of China (Grant Nos. 12073051, 12090041, 12090040, 11733006, 11403061, 11903048, U1631131, 11973060, 12090044, 12073039, 11633009 and U1531118)the Key Laboratory of Optical Astronomy+4 种基金National Astronomical ObservatoriesChinese Academy of Sciencesthe Key Research Program of Frontier Sciences, CAS (Grant No. QYZDY-SSW- SLH007)supports from the Science and Technology Development Fund, Macao SAR (file No. 0007/ 2019/A)Faculty Research Grants of the Macao University of Science and Technology (No. FRG- 19-004-SSI)。
文摘The Large sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) medium-resolution spectral survey of Galactic Nebulae(MRS-N) has conducted for more than three years since 2018 September and observed more than190 thousand nebular spectra and 20 thousand stellar spectra.However,there is not yet a data processing pipeline for nebular spectra.To significantly improve the accuracy of nebulae classification and their physical parameters,we developed the MRS-N Pipeline.This article presented in detail each data processing step of the MRS-N Pipeline,such as removing cosmic rays,merging single exposure,fitting sky light emission lines,wavelength recalibration,subtracting skylight,measuring nebular parameters,creating catalogs and packing spectra.Finally,a description of the data products,including nebular spectra files and parameter catalogs,is provided.
文摘The nature of random errors in any data set is Gaussian, which is a well established fact according to the Central Limit Theorem. Supernovae type Ia data have played a crucial role in major discoveries in cosmology. Unlike in laboratory experiments, astronomical measurements cannot be performed in controlled situations. Thus, errors in astronomical data can be more severe in terms of systematics and non-Gaussianity compared to those of laboratory experiments. In this paper, we use the Kolmogorov-Smiruov statistic to test non-Gaussianity in high-z supernovae data. We apply this statistic to four data sets, i.e., Gold data （2004）, Gold data （2007）, the Union2 catalog and the Union2.1 data set for our analysis. Our results show that in all four data sets the errors are consistent with a Gaussian distribution.
文摘In this work,we present a systematic comp arison of single-and multiple-sc attering models for dust-scattered starlight across the UV sky and attempt to derive a simulation model of multiple-scattered radiation using the single-scattered radiation.Our new simulated multiple-scattering model uses a critical angle(θ_(c)),which is dependent on optical depth(τ),albedo(a),and phase function asymmetry(g),to replace the computationally intensive full Monte Carlo treatment.We find that multiple-scattering becomes increasingly important in almost all optical depths,depending on the scattering geometry.UV-bright stars show a peak scattering intensity near the stellar disk,dropping by an order of magnitude within 10°-15°and merging with the background at 40°-50°,whereas fainter or more distant stars require larger angular separations to reach the same relative reduction.We introduce a functional form,I_(θ)=I_(0)(1-tanh(SP×θ)),to describe the radial decrease in scattered intensity,with the slope parameter declining systematically for more distant stars.Depending on a star's position,multiplescattered fluxes can exceed single-scattered fluxes by up to 200%,and both converge at a critical angle,θ_(c),which depends logarithmically on stellar distance and is governed byτ,a,and g.Notably,θ_(c)remains independent of Galactic longitude or latitude,underscoring the robust,geometry-driven nature of the scattering process.
基金the cosmology simulation database(CSD)in the National Basic Science Data Center(NBSDC)and its funds the NBSDC-DB-10the support from the National Key Research and Development Program of China(2022YFA1602930)+3 种基金the National Natural Science Foundation of China(NSFC,grant Nos.11825303 and 11861131006)the science research grants from the China Manned Space project with No.CMS-CSST 2021-A03,CMSCSST-2021-A04the Fundamental Research Funds for the Central Universities of China(2262022-00216)the startup funding of Zhejiang University。
文摘This study numerically investigates the formation of high-velocity molecular clouds(HVMCs)in the Galactic Center(GC)based on the X-ray emission analysis.We employ three-dimensional magnetohydrodynamic simulations to explore the propagation and acceleration of HVMCs with starburst-driven winds,considering vertical,horizontal,and no magnetic field scenarios.Our results reveal that the envelope gas(with a typical T~10~8 K and density~10^(-2)cm^(-3))of molecular clouds(MCs)as a result of the shock interaction is responsible for X-ray emission.Additionally,some clear boundary exists between the interstellar medium(ISM),envelope gas and MCs,and the envelope gas protects the MCs in the heated environment of the shock wave.In theory,it is challenging to distinguish between the envelope gas,MCs and ISM in terms of X-ray emission.Our simulations suggest that the envelope gas has a significant impact on the survival and emission characteristics of MCs,providing insights into the complex interactions from the supernova feedback mechanisms in the GC.
基金supported by the Strategic Priority Research Program of Chinese Academy of Sciences(grant No.XDA0350502)the National SKA Program of China(No.2020SKA0120103)the National Natural Science Foundation of China(No.U1831130).
文摘Determining accurate pulsar timing model parameters is essential for establishing TT(PT),a realization of Terrestrial Time(TT)based on a pulsar timescale(PT).This study discusses the impact of different data spans on the accuracy of pulsar timing model parameters when determining pulsar timing model parameters.Using observations of PSR J0437-4715,J1909-3744,J1713+0747,and J1744-1134 from the second data release of the International Pulsar Timing Array(IPTA II,Version A),we compare the accuracy of the timing model parameters determined by these observations with different data spans.The results show for PSR J0437-4715,J1713+0747,and J1909-3744,the amplitude fluctuations of rotational frequency remain within 10^(−15),10^(−14),and 10^(−14) Hz,respectively,when the data spans for determining pulsar timing model parameters exceed 13,14,and 6 yr.Additionally,the one-year accuracy of TT(PT)is crucial for its application in timekeeping.By comparing the frequency deviations of TT(PT)relative to TT(BIPM)under both ideal(k_(r))and actual(k_(p))conditions across different data spans,we find that when the data span reaches the duration above,the accuracy of TT(PT)surpasses that of TT(TAI)under ideal conditions,slightly inferior under actual conditions.This suggests with improved observational technologies,the accuracy of TT(PT)can be further enhanced.
基金support by the Fundamental Research Funds for the Central Universities of China (2013/B15020271)the National Natural Science Foundation of China (1014/515029111)the National Undergraduate Training Program for Innovation and Entrepreneurship (201610294069)
文摘With the development of large-scale spectral surveys, fiber positioning technology has been developing rapidly. Because of the performance advantages of a four-quadrant（4Q） detector, a fiber positioning and real-time monitoring system based on the 4Q detector is proposed. The detection accuracy of this system is directly determined by the precision of the center of the spot. A Gaussian fitting algorithm based on the 4Q detector is studied and applied in the fiber positioning process to improve the calculated accuracy of the spot center. The relationship between the center position of the incident spot and the detector output signal is deduced. An experimental platform is built to complete the simulated experiment. Then we use the Gaussian fitting method to process experimental data, compare the fitting value with the theoretical one and calculate the corresponding error.
基金founded by the strategic priority science and technology projects in space science of the Chinese Academy of Sciences (Nos.XDA04040000 and XDA04040400)supported in part by the National Key Research and Development Program of China (2016YFA0400200)+7 种基金the National Basic Research Program of China (No.2013CB837000)the Strategic Priority Research Program of the Chinese Academy of Sciences “Multi-Waveband Gravitational Wave Universe” (No.XDB23040000)Youth Innovation Promotion Association of CASthe National Natural Science Foundation of China (Nos.11525313,11673075,11773086,11303107,11303105,11773085,U1738123,U1738136,U1738207 and U1738210)the Young Elite Scientists Sponsorship program by CAST (No.YESS20160196)the 100 Talents Program of Chinese Academy of Sciencessupport by the Swiss National Science Foundation (SNSF)Switzerland and the National Institute for Nuclear Physics (INFN),Italy
文摘The DArk Matter Particle Explorer（DAMPE）,also known as Wukong in China,which was launched on 2015 December 17,is a new high energy cosmic ray and γ-ray satellite-borne observatory.One of the main scientific goals of DAMPE is to observe Ge V-Te V high energy γ-rays with accurate energy,angular and time resolution,to indirectly search for dark matter particles and for the study of high energy astrophysics. Due to the comparatively higher fluxes of charged cosmic rays with respect to γ-rays,it is challenging to identify γ-rays with sufficiently high efficiency,minimizing the amount of charged cosmic ray contamination. In this work we present a method to identify γ-rays in DAMPE data based on Monte Carlo simulations,using the powerful electromagnetic/hadronic shower discrimination provided by the calorimeter and the veto detection of charged particles provided by the plastic scintillation detector. Monte Carlo simulations show that after this selection the number of electrons and protons that contaminate the selected γ-ray events at～10 Ge V amounts to less than 1% of the selected sample.Finally,we use flight data to verify the effectiveness of the method by highlighting known γ-ray sources in the sky and by reconstructing preliminary light curves of the Geminga pulsar.
基金Supported by the National Natural Science Foundation of China.
文摘Using 64 ms count data of long gamma-ray bursts （T90 〉 2.6 s）, we analyze the quantity named relative spectral lag （RSL）, T31/FWHM（1）. We investigated in detail all the correlations between the RSL and other parameters for a sample of nine long bursts, using the general cross-correlation technique that includes the lag between two different energy bands. We conclude that the distribution of RSLs is normal and has a mean value of 0.1; that the RSLs are weakly correlated with the FWHM, the asymmetry, peak flux （Fp）, peak energy （Ep） and spectral indexes （α and β）, while they are uncorrelated with τ31, the hardness- ratio （HR31） and the peak time （tm）. Our important discovery is that redshift （z） and peak luminosity （Lp） are strongly correlated with the RSL, which can be measured easily and directly, making the RSL a good redshift and peak luminosity indicator.
基金Supported by the National Natural Science Foundation of China
文摘An accurate determination of the landing trajectory of Chang＇e-3 （CE-3） is significant for verifying orbital control strategy, optimizing orbital planning, accu- rately determining the landing site of CE-3 and analyzing the geological background of the landing site. Due to complexities involved in the landing process, there are some differences between the planned trajectory and the actual trajectory of CE-3. The land- ing camera on CE-3 recorded a sequence of the landing process with a frequency of 10 frames per second. These images recorded by the landing camera and high-resolution images of the lunar surface are utilized to calculate the position of the probe, so as to reconstruct its precise trajectory. This paper proposes using the method of trajectory reconstruction by Single Image Space Resection to make a detailed study of the hov- ering stage at a height of 100 m above the lunar surface. Analysis of the data shows that the closer CE-3 came to the lunar surface, the higher the spatial resolution of im- ages that were acquired became, and the more accurately the horizontal and vertical position of CE-3 could be determined. The horizontal and vertical accuracies were 7.09 m and 4.27 m respectively during the hovering stage at a height of 100.02 m. The reconstructed trajectory can reflect the change in CE-3＇s position during the powered descent process. A slight movement in CE-3 during the hovering stage is also clearly demonstrated. These results will provide a basis for analysis of orbit control strategy, and it will be conducive to adjustment and optimization of orbit control strategy in follow-up missions.
基金Under the auspices of Natural Science Foundation of China(No.42071342,31870713)Beijing Natural Science Foundation Program(No.8182038)Fundamental Research Funds for the Central Universities(No.2015ZCQ-LX-01,2018ZY06)。
文摘With the continuous development of urbanization in China,the country’s growing population brings great challenges to urban development.By mastering the refined population spatial distribution in administrative units,the quantity and agglomeration of population distribution can be estimated and visualized.It will provide a basis for a more rational urban planning.This paper takes Beijing as the research area and uses a new Luojia1-01 nighttime light image with high resolution,land use type data,Points of Interest(POI)data,and other data to construct the population spatial index system,establishing the index weight based on the principal component analysis.The comprehensive weight value of population distribution in the study area was then used to calculate the street population distribution of Beijing in 2018.Then the population spatial distribution was visualize using GIS technology.After accuracy assessments by comparing the result with the WorldPop data,the accuracy has reached 0.74.The proposed method was validated as a qualified method to generate population spatial maps.By contrast of local areas,Luojia 1-01 data is more suitable for population distribution estimation than the NPP/VIIRS(Net Primary Productivity/Visible infrared Imaging Radiometer)nighttime light data.More geospatial big data and mathematical models can be combined to create more accurate population maps in the future.
文摘Forbush decrease(FD),discovered by Scott E.Forbush about 80 years ago,is referred to as the non-repetitive short-term depression in Galactic cosmic ray(GCR)flux,presumed to be associated with large-scale perturbations in solar wind and interplanetary magnetic field(IMF).It is the most spectacular variability in the GCR intensity which appears to be the compass for investigators seeking solar-terrestrial relationships.The method of selection and validation of FD events is very important to cosmic ray(CR)scientists.We have deployed new computer software to determine the amplitude and timing of FDs from daily-averaged CR data at Oulu Neutron Monitor station.The code selected 230 FDs between 1998 and 2002.In an attempt to validate the new FD automated catalog,the relationship between the amplitude of FDs,and IMF,solar wind speed(SWS)and geomagnetic storm indices(Dst,kp,ap)is tested here.A two-dimensional regression analysis indicates significant linear relationship between large FDs(CR(%)≤-3)and solar wind data and geomagnetic storm indices in the present sample.The implications of the relationship among these parameters are discussed.
基金Supported by the National Natural Science Foundation of China.
文摘An unusual timing and spectral state of a black hole microquasar XTE J1550- 564 observed with RXTE is analyzed. Millisecond variabilities are found, which are significantly shorter than the minimum possible time scale in the light curves of black hole binaries, as suggested by Sunyaev ＆ Revnivtsev （2000）. The X-ray spectral fitting result indicates that there is an unusual soft component in the spectrum, which may be responsible for the millisecond variabilities. The millisecond variabilities as well as the unusual soft spectral component should be produced from some small, but independent active regions in the accretion disk.
基金supported partly by project DN08/20 of the Scientific Foundation of the Bulgarian Ministry of Education and Scienceby project RD 08-142 of Shumen University+1 种基金the support of the private IRIDA Observatory operated remotely(www.iridaobservatory.org)Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement
文摘We present photometric observations in Sloan filters g′, i′of the eclipsing W UMa stars USNOA2.0 1350-17365531, V471 Cas, V479 Lac and V560 Lac. The sinusoidal-like O-C diagram of V471 Cas indicates the presence of a third body with mass 0.12 M_⊙(a red dwarf) at distance 897 R_⊙. The O-C diagram of V479 Lac reveals a period decrease of d P/dt =-1.69 × 10-6d yr-1. The results of the light curve solutions are:(i) the targets are overcontact binaries with small fill-out factors;(ii) their components are F–K stars, comparable in size, whose temperature differences are below 80 K;(iii) all targets undergo partial eclipses and to limit the possible mass ratios we carried out two-step q-search analysis. The target global parameters(luminosities, radii, masses) were obtained on the basis of their Gaia distances and the results of our light curve solutions. The obtained total mass of V560 Lac turns out to be smaller than the lower mass limit for presently known W UMa binaries of 1.0-1.2 M_⊙, i.e. this target is a peculiar overcontact system.
