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An Impulsive Heating Model for the Evolution of Coronal Loops

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Chinese Journal of Astronomy and Astrophysics 2006年第5期6卷 608-616页

作者： Li Feng wei-qun gan Purple Mountain Observatory Chinese Academy of Sciences Nanjing 210008 Max Planck Institute for Solar System Research Max-Planck-Str. 2 37191 Katlenburg-LindauGermany

It was suggested by Parker that the solar corona is heated by many small energy release events generally called microflares or nanoflares. More and more observations showed flows and intensity variations in nonflaring loops. Both theories and observations have indicated that the heating of coronal loops should actually be unsteady. Using SOLFTM （Solar Flux Tube Model）, we investigate the hydrodynamics of coronal loops undergoing different manners of impulsive heating with the same total energy deposition. The half length of the loops is 110 Mm, a typical length of active region loops. We divide the loops into two categories： loops that experience catastrophic cooling and loops that do not. It is found that when the nanoflare heating sources are in the coronal part, the loops are in non-catastrophic-cooling state and their evolutions are similar. When the heating is localized below the transition region, the loops evolve in quite different ways. It is shown that with increasing number of heating pulses and inter-pulse time, the catastrophic cooling is weakened, delayed, or even disappears altogether.

关键词： hydrodynamics -- Sun corona -- Sun transition region

Multi-wavelength Diagnostics of Bombardment by Non-thermal Particles in Solar Flares

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Chinese Journal of Astronomy and Astrophysics 2005年第5期5卷 519-530页

作者： Zhi Xu Cheng Fang wei-qun gan Astronomy Department of Nanjing University Nanjing 210093 Purple Mountain Observatory Chinese Academy of Sciences Nanjing 210008

Chromospheric lines, including Ha, Lya, Lyβ and CaⅡ K, CaⅡ 8542, are systemically and quantitatively investigated with respect to the non-thermal excitation and ionization due to particle beam bombardment for a series of solar semi-empirical atmospheric models. As a result we propose to use the contrast in the integrated intensity of hydrogen lines to estimate the total energy flux of the bombarding beam during the solar flare impulsive phase. Partial frequency redistribution is considered in the Lyα line calculation and a smaller intensity en- hancement in the Hα line-centers is found than in the previous results of Fang et al.

关键词： Sun: flare- Sun: chromosphere

Double hard X-ray peaks in RHESSI flares as evidence of chromospheric evaporation and implications for modifying the Neupert effect

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Research in Astronomy and Astrophysics 2009年第10期9卷 1155-1164页

作者： You-Ping Li wei-qun gan Yang Su Purple Mountain Observatory Chinese Academy of Sciences Nanjing 210008 China

Among the RHESSI flare samples, we concentrated on a kind of flare that presents two successive peaks （that is, it presents both an impulsive phase and a gradual phase） in 12 - 25 keV light curves. Taking the C1.4 flare on 2002 August 12 as an example, we studied the light curves, spectra, and images in detail. Making full use of the capabilities of RHESSI, we showed some evidence to support the expected causal relationship between these two peaks; the first peak is mainly nonthermal, while the second peak is mainly thermal; the energy carried by nonthermal electrons during the first peak seems to be comparable to the thermal energy of the second peak. The morphologies of X-ray images and their evolutions provide additional evidence for this causality. We conclude that two such peaks in the 12 - 25 keV light curve are good evidence for the chromospheric evaporation. However, the maximum time of the second peak is later than the end time of the first peak, suggesting that for some events, a modification of the traditional Neupert effect could be necessary by inclusion of a time delay, which might be partly related to the filling of the loop by evaporated material.

关键词： Sun flares -- Sun X-rays, gamma-rays

Joint hard X-ray observations with ASO-S/HXI and SO/STIX

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Research in Astronomy and Astrophysics 2019年第11期19卷 127-130页

作者： Sam Krucker Gordon JHurford Yang Su wei-qun gan University of Applied Sciences and Arts Northwestern Switzerland Bahnhofstrasse 65210WindischSwitzerland Space Science Laboratory University of California7 Gauss Way94720 BerkeleyUSA Key Laboratory of Dark Matter and Space Astronomy Purple Mountain ObservatoryChinese Academy of SciencesNanjing 210034China

This paper discusses the potential of future joint hard X-ray solar flare observations between the Hard X-ray Imager(HXI)onboard the Advanced Space-based Solar Observatory(ASO-S)mission and the Spectrometer/Telescope for Imaging X-rays(STIX)on Solar *** different viewing perspectives of the two telescopes relative to the Sun will allow us for the first time to systematically study non-thermal hard X-ray emissions *** the 4-years of the nominal mission of ASO-S,we expect to jointly observe about 160 flares above GOES M1 class to systematically study hard X-ray *** about 16 partially limb-occulted STIX flares,we will have observations of the entire flare by *** observations will enable us to simultaneously study the all-important coronal hard X-ray sources,which are generally lost in the instrument’s individual imaging dynamic range,in combination with the chromospheric footpoint *** two different detector systems used in the two telescopes make the relative calibration between the two instruments a key task that needs to be addressed before creditable science results can be *** an accurate inter-calibration can be achieved using jointly observed flares on the disk,observations with HXI and STIX will provide new and essential key diagnostics for solar flare physics.

关键词： Sun flares

Study of a solar flare on 2005 August 22 observed in hard X-rays and microwaves

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Research in Astronomy and Astrophysics 2015年第1期15卷 64-76页

作者： Zhong-Yin Liu You-Ping Li wei-qun gan Kazi A.Firoz Key Laboratory of Dark Matter and Space Astronomy Purple Mountain Observatory Chinese Academy of Sciences Space Research Group Alcala University28871 Alcala de Henares Spain

We investigate the 2005 August 22 flare event（00：54 UT） exploiting hard X-ray（HXR） observations from the Reuven Ramaty High Energy Solar Spectroscopic Imager（RHESSI） and microwave（MW） observations from the Nobeyama Solar Radio Observatory. The HXR time profile exposes well-damped quasi-periodic pulsations with four sequential peaks, and the MW time profile follows the corresponding *** on this feature, we derive the time relationship of HXRs and MWs with multifrequency data from the Nobeyama Radio Polarimeter, and the spatially resolvable data from RHESSI and the Nobeyama Radioheliograph. We find that both frequency dependent delays in MWs and energy dependent delays in HXRs are ***, MW emissions from the south source are delayed with respect to those from the north source at both 17 GHz and 34 GHz, but no significant delays are found in HXR emissions from the different sources at the same energies. To better understand all these long time delays, we derive the electron fluxes of different energies by fitting the observed HXR spectra with a single power-law thick-target model, and speculate that these delays might be related to an extended acceleration process. We further compare the time profile of a MW spectral index derived from 17 and 34 GHz fluxes with the flux densities, and find that the spectral index shows a strong anticorrelation with the HXR fluxes.

关键词： Sun: flares Sun: radio radiation Sun: X-rays,gamma rays

Preface:Advanced Space-based Solar Observatory(ASO-S)

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Research in Astronomy and Astrophysics 2019年第11期19卷 1-2页

作者： wei-qun gan Ming-De Ding Yu Huang Ying-Na Su Key Laboratory of Dark Matter and Space Astronomy Purple Mountain ObservatoryChinese Academy of SciencesNanjing 210034China School of Astronomy and Space Science Nanjing UniversityNanjing 210023China

The Advanced Space-based Solar Observatory(ASO-S)is the first approved solar space mission in *** special issue includes a total of 13 papers,which were selected from presentations at the First ASO-S International Workshop,held in Nanjing from 2019 January 15 to *** together,these 13 papers provide a complete description of ASO-S until the end of Phase-B and the beginning of Phase-C.

关键词： space vehicles instruments Sun magnetic fields flares CMEs UV radiation X-ray,gamma-rays

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

On the power-law distributions of X-ray fluxes from solar flares observed with GOES

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Research in Astronomy and Astrophysics 2016年第10期16卷 99-106页

作者： You-Ping Li Li Feng Ping Zhang Si-Ming Liu wei-qun gan Key Laboratory of Dark Matter and Space Astronomy Purple Mountain ObservatoryChinese Academy of Sciences

The power-law frequency distributions of the peak flux of solar flare X-ray emission have been studied extensively and attributed to a system having self-organized criticality （SOC）. In this paper, we first show that, so long as the shape of the normalized light curve is not correlated with the peak flux, the flux histogram of solar flares also follows a power-law distribution with the same spectral index as the power- law frequency distribution of the peak flux, which may partially explain why power-law distributions are ubiquitous in the Universe. We then show that the spectral indexes of the histograms of soft X-ray fluxes observed by GOES satellites in two different energy channels are different： the higher energy channel has a harder distribution than the lower energy channel, which challenges the universal power-law distribution predicted by SOC models and implies a very soft distribution of thermal energy content of plasmas probed by the GOES satellites. The temperature （T） distribution, on the other hand, approaches a power-law dis- tribution with an index of 2 for high values of T. Hence the application of SOC models to the statistical properties of solar flares needs to be revisited.

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

Solar flares with similar soft but different hard X-ray emissions： case and statistical studies

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Research in Astronomy and Astrophysics 2016年第1期16卷 39-50页

作者： Ivan N.Sharykin Alexei B.Struminsky Ivan V.Zimovets wei-qun gan Space Research Institute Russian Academy of Sciences Moscow 117997 Russia Purple Mountain Observatory Chinese Academy of Sciences Nanjing 210008 China

From the Reuven Ramaty High Energy Solar Spectroscopic Imager （RHESS1） catalog we select events which have approximately the same GOES class （high C - low M or 500-1200 counts s-1 within the RHESSI 6-12 keV energy band）, but with different maximal energies of detected hard X-rays. The selected events are subdivided into two groups：（1） flares with X-ray emissions observed by RHESSI up to only 50 keV and （2） flares with hard X-ray emission observed also above 50 keV. The main task is to understand observational peculiarities of these two flare groups. We use RHESSIX-ray data to obtain spectral and spa- tial information in order to find differences between selected groups. Spectra and images are analyzed in detail for six events （case study）. For a larger number of samples （85 and 28 flares in the low-energy and high-energy groups respectively） we only make some generalizations. In spectral analysis we use the thick- target model for hard X-ray emission and one temperature assumption for thermal soft X-ray emission. RHESSI X-ray images are used for determination of flare region sizes. Although thermal and spatial prop- erties of these two groups of flares are not easily distinguishable, power law indices of hard X-rays show significant differences. Events from the high-energy group generally have a harder spectrum. Therefore, the efficiency of chromospheric evaporation is not sensitive to the hardness of nonthermal electron spectra but rather depends on the total energy flux of nonthermal electrons.

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