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Observational evidence of magnetic reconnection in a coronal bright point

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Research in astronomy and Astrophysics 2020年第9期20卷 171-182页

作者： Zong-Jun Ning Dong Li Qing-Min Zhang key laboratory of dark matter and space astronomy Purple Mountain ObservatoryNanjing 210033China

Magnetic reconnection is considered to be the fundamental process by which magnetic energy is converted into plasma or particle kinetic *** reconnection is a widely applied physics model to explain the solar eruption events,such as coronal bright points(CBPs).Meanwhile,it is an usual way of the solar physics research to look for the observational evidences of magnetic reconnection in the solar eruption events in order to support the *** this paper,we have explored the evidences of magnetic reconnection in a CBP observed by the Atmospheric Imaging Assembly(AIA)onboard the Solar Dynamics Observatory(SDO)at NOAA No.11163 on 2011 March *** observations show that this event is a small-scale loop system in active regions that have similar size as a traditional CBP and it might shed light on the physics of a traditional *** CBP is bright in all nine AIA wavelengths and displays a flaring development with three bursts *** burst exhibits a pair of bi-directional jets almost along a *** originate from the same position(CBP core),then move in the opposite *** findings are well consistent with the magnetic reconnection process by which the bi-directional plasma outflows are produced and radiate the bi-directional jets detected by SDO/*** facts further support the conclusion that the CBP is produced by the magnetic reconnection process.

关键词： Sun:UV radiation Sun:corona Sun:oscillation

Interpretation of the DAMPE 1.4 Te V peak according to the decaying dark matter model

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Science China(Physics,Mechanics & astronomy) 2018年第10期61卷 36-42页

作者： Xu Pan Cun Zhang Lei Feng key laboratory of dark matter and space astronomy Purple Mountain Observatory Chinese Academy of Sciences School of Physics Nanjing University

Highly accurate measurements of cosmic ray electron flux by the dark matter particle explorer （DAMPE） ranging between 25 GeV and 4.6 TeV have recently been published. A sharp peak structure was found at - 1.4 TeV. This unexpected peak structure can be reproduced by the annihilation/decay of a nearby dark matter （DM） halo. In this study, we adopt the decaying-DM model to interpret the - 1.4 TeV peak. We found that the decay products of the local DM subhalo could contribute to the DMAPE peak with mDM = 3 TeV and r - 10^28 s. We also obtain constraints on DM lifetime and the distance of the local DM subhalo by comparison with DAMPE data.

关键词： dark matter cosmic ray DAMPE

The effect of Compton scattering on gamma-ray spectra of the 2005 January 20 flare

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Research in astronomy and Astrophysics 2012年第10期12卷 1439-1450页

作者： Wei Chen Wei-Qun Gan key laboratory of dark matter and space astronomy Purple Mountain Observatory ChineseAcademy of Sciences Nanjing 210008 China

Gamma-ray spectroscopy provides a wealth of information about acceler- ated particles in solar flares, as well as the ambient medium with which these energetic particles interact. The neutron capture line （2.223 MeV）, the strongest in the solar gamma-ray spectrum, forms in the deep atmosphere. The energy of these photons can be reduced via Compton scattering. With the fully relativistic GEANT4 toolkit, we have carried out Monte Carlo simulations of the transport of a neutron capture line in solar flares, and applied them to the flare that occurred on 2005 January 20 （X7.1/2B）, one of the most powerful gamma-ray flares observed by RHESSI during the 23rd solar cycle. By comparing the fitting results of different models with and without Compton scattering of the neutron capture line, we find that when including the Compton scat- tering for the neutron capture line, the observed gamma-ray spectrum can be repro- duced by a population of accelerated particles with a very hard spectrum （s ≤ 2.3）. The Compton effect of a 2.223 MeV line on the spectra is therefore proven to be sig- nificant, which influences the time evolution of the neutron capture line flux as well. The study also suggests that the mean vertical depth for neutron capture in hydrogen for this event is about 8 g cm-2.

关键词： Sun: flares -- Sun: gamma-rays -- scattering: Compton scattering

Statistical study of co-rotating interaction region properties with STEREO and ACE observations

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Research in astronomy and Astrophysics 2017年第11期17卷 19-26页

作者： Yu Huang Qi-Wu Song Dong Li key laboratory of dark matter and space astronomy Purple Mountain Observatory Chinese Academy of Sciences Nanjing 210008 China

We analyzed the data on co-rotating interaction regions （CIRs） measured by the Advanced Composition Explorer （ACE） and Solar TErrestrial RElations Observatory （STEREO） from 2007 to 2010. The CIRs were observed by STEREO B （STB）, ACE and STEREOA （STA） one after another, and a total of 28 CIRs were identified in this work. Since the same characteristics of CIRs were detected by these three spacecraft at three different locations and times, these data can help us to study the evolutions of CIRs. For a single event, the properties of CIRs observed by the three spacecraft were quite different and could be explained by spatial or temporal variations. For all these 28 CIRs, STA and STB observed similar mean parameters, such as peak magnetic field strength （offset 11%）, peak and change in solar wind speed （offset 3% and 10% respectively）, peak proton temperature （offset 14%） and peak perpendicular pressure （offset 15%）. Surprisingly, STA detected much higher （41%） peak density of protons than STB.

关键词： Sun: solar wind -- Sun: rotation -- Sun: magnetic fields -- Sun: atmosphere -- Sun:evolution

The breakdown of the power-law frequency distributions for the hard X-ray peak count rates of solar flares

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Research in astronomy and Astrophysics 2013年第12期13卷 1482-1492页

作者： You-Ping Li Wei-Qun Gan Li Feng Si-Ming Liu A.Struminsky key laboratory of dark matter and space astronomy Purple Mountain ObservatoryChinese Academy of Sciences space Research Institute(IKI) Russian Academy of Science

The frequency distribution for several characteristics of a solar flare obeys a power law only above a certain threshold, below which there is an apparent loss of small scale events presumably caused by limited instrumental sensitivity and th：e corresponding event selection bias. It is also possible that this deviation in the power law can have a physical origin in the source. We propose two fitting models incorpo- rating a power law distribution with a low count rate cutoff plus a noise component for the frequency distribution of the hard X-ray peak count rate of all solar flare sam- ples obtained with HXRBS/SMM and BATSE/CGRO observations. Our new fitting method produces the same power-law index as previously developed methods, a low cutoff of the power-law function and its corresponding noise level, which is consistent with measurements of the actual noise level of the hard X-ray count rate. We found that the fitted low cutoff appears to be related to the noise level, i.e., flares are only recognized when their peak count rate is 3or greater than noise. Therefore, the fitted low cutoff, which is smaller than the aforementioned threshold, might be attributed to selection bias, and probably not to the actual count rate cutoff in flares at smaller scales. Whether or not the actual low cutoff physically exists needs to be checked by future observations with increased sensitivities.

关键词： Sun: flares -- Sun: X-rays gamma-rays -- methods: statistical

Design of a high-dynamic-range prototype readout system for VLAST calorimeter

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Nuclear Science and Techniques 2023年第10期34卷 47-59页

作者： Qiang Wan Jian-Hua Guo Xing Xu Shen Wang Yong-Qiang Zhang Yi-Ming Hu Yan Zhang Xu Pan Xiang Li Chuan Yue Wei Jiang Yu-Xin Cui Deng-Yi Chen key laboratory of dark matter and space astronomy Purple Mountain ObservatoryChinese Academy of SciencesNanjing 210023China School of astronomy and space Science University of Science and Technology of ChinaHefei 230026China

In the future, the Very Large Area gamma-ray space Telescope is expected to observe high-energy electrons and gamma rays in the MeV to TeV range with unprecedented acceptance. As part of the detector suite, a high-energy imaging calorimeter(HEIC) is currently being developed as a homogeneous calorimeter that utilizes long bismuth germanate(BGO) scintillation crystals as both absorbers and detectors. To accurately measure the energy deposition in the BGO bar of HEIC, a highdynamic-range readout method using a silicon photomultiplier(SiPM) and multiphotodiode(PD) with different active areas has been proposed. A prototype readout system that adopts multichannel charge measurement ASICs was also developed to read out the combined system of SiPMs and PDs. Preliminary tests confirmed the feasibility of the readout scheme, which is expected to have a dynamic range close to 10~6.

关键词： VLAST Calorimeter Readout system Front-end electronics Large dynamic range

The spatial distribution of dark matter annihilation originating from a gamma-ray line signal

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Research in astronomy and Astrophysics 2014年第5期14卷 520-526页

作者： Tong-Suo Lu Tie-Kuang Dong Jian Wu key laboratory of dark matter and space astronomy Purple Mountain Observatory Chinese Academy of Sciences Graduate University of Chinese Academy of Sciences

The GeV-TeV -γ-ray line signal is the smoking gun signature of dark matter annihilation or decay. The detection of such a signal is one of the main targets of some space-based telescopes, including Fermi-LAT and the upcoming missions CALET, DAMPE and Gamma-400. An important feature of γ-ray line photons that originate from dark-matter-annihilation is that they are concentrated at the center of the Galaxy. So far, no reliable γ-ray line has been detected by Fermi-LAT, and the upper limits on the cross section of annihilation into ＂y-rays have been reported. We use these upper limits to estimate the ＂maximal＂ number of -y-ray line photons detectable for Fermi- LAT, DAMPE and Gamma-400, and then investigate the spatial distribution of these photons. We show that the center of the distribution will usually be offset from the Galactic center （Sgr A＊） due to the limited statistics. Such a result is almost indepen- dent of models of the dark matter distribution, and will render the reconstruction of the dark matter distribution with the γ-ray line signal very challenging for foreseeable space-based detectors.

关键词： cosmology observations -- cosmology dark matter -- Galaxy center-- instrumentation detectors

Implications on cosmic ray injection and propagation parameters from Voyager/ACE/AMS-02 nucleus data

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Science China(Physics,Mechanics & astronomy) 2019年第4期62卷 98-105页

作者： Qiang Yuan key laboratory of dark matter and space astronomy Purple Mountain Observatory Chinese Academy of Sciences School of astronomy and space Science University of Science and Technology of China Center for High Energy Physics Peking University

We study the propagation and injection models of cosmic rays using the latest measurements of the boron-to-carbon ratio and fluxes of protons, helium, carbon, and oxygen nuclei by the Alpha Magnetic Spectrometer and the Advanced Composition Explorer at top of the Earth, and the Voyager spacecraft outside the heliosphere. The Advanced Composition Explorer(ACE) data during the same time interval of the AMS-02 data are extracted to minimize the complexity of the solar modulation effect. We find that the cosmic ray nucleus data favor a modified version of the diffusion-reacceleration scenario of the propagation. The diffusion coefficient is, however, required to increase moderately with decreasing rigidity at low energies, which has interesting implications on the particle and plasma interaction in the Milky Way. We further find that the low rigidity(< a few GV) injection spectra are different for different compositions. The injection spectra are softer for lighter nuclei. These results are expected to be helpful in understanding the acceleration process of cosmic rays.

关键词： cosmic rays propagation origin and acceleration data analysis

Simulation study of the performance of the Very Large Area gamma-ray space Telescope

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Nuclear Science and Techniques 2024年第9期35卷 1-17页

作者： Xu Pan Wei Jiang Chuan Yue Shi-Jun Lei Yu-Xin Cui Qiang Yuan key laboratory of dark matter and space astronomy Purple Mountain ObservatoryChinese Academy of SciencesNanjing 210023China School of astronomy and space Science University of Science and Technology of ChinaHefei 230026China

The Very Large Area gamma-ray space Telescope(VLAST)is a mission concept proposed to detect gamma-ray photons through both Compton scattering and electron–positron pair production mechanisms,thus enabling the detection of photons with energies ranging from MeV to *** project aims to conduct a comprehensive survey of the gamma-ray sky from a low-Earth orbit using an anti-coincidence detector,a tracker detector that also serves as a low-energy calorimeter,and a high-energy imaging *** developed a Monte Carlo simulation application of the detector using the GEANT4 toolkit to evaluate the instrument performance,including the effective area,angular resolution,and energy resolution,and explored specific optimizations of the detector *** simulation-based analysis indicates that the current design of the VLAST is physically feasible,with an acceptance above 10 m^(2)sr which is four times larger than that of the Fermi-LAT,an energy resolution better than 2%at 10 GeV,and an angular resolution better than 0.2◦at 10 *** VLAST project promises to make significant contributions to the field of gamma-ray astronomy and enhance our understanding of the cosmos.

关键词： space astronomy Gamma-ray telescope Calorimeter Monte Carlo simulation