The Hard X-ray Imager(HXI)payload,a component of China’s Advanced Space-based Solar Observatory satellite,is designed to observe solar X-ray emissions in the 30-200 keV range,with the aim of investigating nonthermal ...The Hard X-ray Imager(HXI)payload,a component of China’s Advanced Space-based Solar Observatory satellite,is designed to observe solar X-ray emissions in the 30-200 keV range,with the aim of investigating nonthermal physical processes during solar flares.Before launch,Geant4 simulations were employed to assess the onorbit background of the HXI instrument,evaluating its performance and potential to achieve its scientific objectives.This study addresses issues identified in previous simulations and conducts further analyses to examine the distribution of background counts across the 99 detectors.The results demonstrate alignment between simulations and observations at low and medium geomagnetic latitudes;however,challenges persist at high geomagnetic latitudes due to limitations in the current albedo photon model.This investigation provides insights into background sources from various particles,enhances understanding of space background characteristics,and offers guidance for background subtraction in imaging processes.展开更多
Early multiwavelength observations offer crucial insights into the nature of the relativistic jets responsible for gamma-ray bursts and their interaction with the surrounding medium.We present data of GRB 240825A from...Early multiwavelength observations offer crucial insights into the nature of the relativistic jets responsible for gamma-ray bursts and their interaction with the surrounding medium.We present data of GRB 240825A from 17 space-and ground-based telescopes/instruments,covering wavelengths from NIR/optical to X-ray and GeV,and spanning from the prompt emission to the afterglow phase triggered by Swift and Fermi.The early afterglow observations were carried out by SVOM/C-GFT,and spectroscopic observations of the afterglow by GTC,VLT,and TNG determined the redshift of the burst(z=0.659)later.A comprehensive analysis of the prompt emission spectrum observed by Swift-BAT and Fermi-GBM/LAT reveals a rare and significant high-energy cutoff at 76 MeV.Assuming this cutoff is due toγγabsorption allows us to place an upper limit on the initial Lorentz factor,Γ_(0)<245.The optical/NIR and GeV afterglow light curves can be described by the standard external shock model,with early-time emission dominated by a reverse shock(RS)and a subsequent transition to forward shock(FS)emission.Our afterglow modeling yields a consistent estimate of the initial Lorentz factor(Γ_(0)∼234).Furthermore,the RS-to-FS magnetic field ratio(R 302B)indicates that the RS region is significantly more magnetized than the FS region.An isotropic-equivalent kinetic energy of E_(k,iso)=5.25×10^(54) erg is derived,and the correspondingγ-ray radiation efficiency is estimated to beη_(γ)=3.1%.On the other hand,the standard afterglow model cannot reproduce the X-ray light curve of GRB 240825A,calling for improved models to characterize all multiwavelength data.展开更多
Supernova remnants(SNRs)interacting with molecular clouds(MCs)are recognized as the sources of γ-rays and cosmic rays in the Galaxy.Based on the SNR-MC system,this study establishes a particle cumulative diffusion mo...Supernova remnants(SNRs)interacting with molecular clouds(MCs)are recognized as the sources of γ-rays and cosmic rays in the Galaxy.Based on the SNR-MC system,this study establishes a particle cumulative diffusion model to investigate the mechanism by which high-energy protons escaping from SNRs interact with dense MCs through proton–proton interactions to produce high-energyγ-rays.Using the W51 complex,a typical star-forming region,as a research sample,we analyze the production and propagation characteristics of γ-rays.By employing the Exponential Cutoff Power-Law model and the Markov Chain Monte Carlo method,we fit theγ-ray observational data of W51C,successfully constraining the key physical parameters.Additionally,we systematically search for 1LHAASO sources spatially coincident with SNR-MC systems to explore the potential origins of ultra-high-energy(UHE) γ-ray sources.The results indicate that the radiation characteristics of the UHE γ-ray sources are highly consistent with the SNR-MC systems,further supporting their candidacy as PeVatrons in the Galaxy.展开更多
The study of high-energy gamma-ray emission from gamma-ray bursts(GRBs)involves complex synchrotron radiation and synchrotron self-Compton(SSC)scattering mechanisms with multiple parameters exhibiting a wide distribut...The study of high-energy gamma-ray emission from gamma-ray bursts(GRBs)involves complex synchrotron radiation and synchrotron self-Compton(SSC)scattering mechanisms with multiple parameters exhibiting a wide distribution.Recent advancements in GRB research,particularly the observation of very high energy(VHE,>100 Ge V)radiation,have ushered in a new era of multiwavelength exploration,offering fresh perspectives and limitations for understanding GRB radiation mechanisms.This study aimed to leverage VHE observations to refine constraints on synchrotron+SSC radiation from electrons accelerated by forward shocks.By analyzing two external environments—the uniform interstellar medium and stratified stellar wind medium,we conducted spectral and variability fitting for five specific bursts(GRB 180720B,GRB 190114C,GRB 190829A,GRB 201216C,and GRB 221009A)to identify the optimal parameters characterizing these events.A comparative analysis of model parameter distributions with and without VHE radiation observations reveals that the magnetic energy equipartition factorεBis more concentrated with VHE emissions.This suggests that VHE emissions may offer greater constraints on this microphysical parameter.Additionally,we found that the energy budget between VHE and ke V–Me Vγ-ray emissions under the SSC radiation exhibits an almost linear relationship,which may serve as a tool to differentiate radiation mechanisms.We anticipate future statistical analyses of additional VHE bursts to validate our findings.展开更多
We perform a time-resolved statistical study of GRB 221009A’s X-ray emission using Swift XRT Photon Counting and Windowed Timing data.After standard reduction(barycentric correction,pile-up,background subtraction via...We perform a time-resolved statistical study of GRB 221009A’s X-ray emission using Swift XRT Photon Counting and Windowed Timing data.After standard reduction(barycentric correction,pile-up,background subtraction via HEASOFT),we extracted light curves for each observational ID and for their aggregation.Countrate histograms were fitted using various statistical distributions;fit quality was assessed by chi-squared and the Bayesian Information Criterion.The first observational segment is best described by a Gaussian distribution(χ^(2)=68.4;BIC=7651.2),and the second by a Poisson distribution(χ^(2)=33.5;BIC=4413.3).When all segments are combined,the lognormal model provides the superior fit(χ^(2)=541.9;BIC=34365.5),indicating that the full data set’s count rates exhibit the skewness expected from a multiplicative process.These findings demonstrate that while individual time intervals conform to discrete or symmetric statistics,the collective emission profile across multiple observations is better captured by a lognormal distribution,consistent with complex,compounded variability in GRB afterglows.展开更多
基金supported by the National Natural Science Foundation of China(NSFC,grant Nos.12173100,11973097 and 12022302)the Youth Innovation Promotion Association CAS(Nos.2021317 and Y2021087)+1 种基金the Scientific Instrument Developing Project of the CAS(No.20200077)the Strategic Priority Research Program on Space Science,Chinese Academy of Sciences(No.XDA 15320104).
文摘The Hard X-ray Imager(HXI)payload,a component of China’s Advanced Space-based Solar Observatory satellite,is designed to observe solar X-ray emissions in the 30-200 keV range,with the aim of investigating nonthermal physical processes during solar flares.Before launch,Geant4 simulations were employed to assess the onorbit background of the HXI instrument,evaluating its performance and potential to achieve its scientific objectives.This study addresses issues identified in previous simulations and conducts further analyses to examine the distribution of background counts across the 99 detectors.The results demonstrate alignment between simulations and observations at low and medium geomagnetic latitudes;however,challenges persist at high geomagnetic latitudes due to limitations in the current albedo photon model.This investigation provides insights into background sources from various particles,enhances understanding of space background characteristics,and offers guidance for background subtraction in imaging processes.
基金supported by the National Key R&D Program of China(grant No.2024YFA1611600)the SVOM project(a mission under the Strategic Priority Program on Space Science of the Chinese Academy of Sciences)+23 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(grant No.XDB0550401)the National Natural Science Foundation of China(NSFC,grant No.12494573)partly supported by Natural Science Foundation of Xinjiang Uygur Autonomous Region(grant No.2024D01D32)Tianshan Talent Training Program(grant No.2023TSYCLJ0053)Tianshan Innovation Team Program(grant No.2024D14015)supported by the Jiangsu Funding Program for Excellent Postdoctoral Talent(grant No.2024ZB110)the Postdoctoral Fellowship Program(grant No.GZC20241916)the General Fund(grant No.2024M763531)of the China Postdoctoral Science Foundationsupported by a Royal Society Dorothy Hodgkin Fellowship(grant Nos.DHF-R1-221175 and DHF-ERE-221005)support by a postdoctoral fellowship from the CNESsupported by the National Key R&D Program of China(grant No.2024YFA1611702)the Strategic Priority Research Program of the Chinese Academy of Sciences(grant No.XDB0550101)the support of the French Agence Nationale de la Recherche(ANR),under grant ANR-23-CE31-0011(project PEGaSUS)financial support from the GRAWITA Large Program Grant(PI P.D’Avanzo)financial support from the Italian Space Agency,contract ASI/INAF No.I/004/11/6support from the INAF project Premiale Supporto Arizona&Italiasupported by the National Natural Science Foundation of China(NSFC,grant No.12133003)supported by the National Natural Science Foundation of China(NSFC,grant No.12373042)the Bagui Scholars Program(No.GXR-6BG2424001)funded by the European Union(ERC,HEAVYMETAL,101071865,Views and opinions expressed are,however,those of the authors only and do not necessarily reflect those of the European Union or the European Research Council Neither the European Union nor the granting authority can be held responsible for them)the Cosmic Dawn Center(DAWN)is funded by the Danish National Research Foundation under grant No.DNRF140supported by the National Natural Science Foundation of China(NSFC,grant Nos.12225305 and 12321003)supported by the National Natural Science Foundation of China(NSFC,grant No.12473049)supported by the General Fund(grant No.2024M763530)of the China Postdoctoral Science Foundation。
文摘Early multiwavelength observations offer crucial insights into the nature of the relativistic jets responsible for gamma-ray bursts and their interaction with the surrounding medium.We present data of GRB 240825A from 17 space-and ground-based telescopes/instruments,covering wavelengths from NIR/optical to X-ray and GeV,and spanning from the prompt emission to the afterglow phase triggered by Swift and Fermi.The early afterglow observations were carried out by SVOM/C-GFT,and spectroscopic observations of the afterglow by GTC,VLT,and TNG determined the redshift of the burst(z=0.659)later.A comprehensive analysis of the prompt emission spectrum observed by Swift-BAT and Fermi-GBM/LAT reveals a rare and significant high-energy cutoff at 76 MeV.Assuming this cutoff is due toγγabsorption allows us to place an upper limit on the initial Lorentz factor,Γ_(0)<245.The optical/NIR and GeV afterglow light curves can be described by the standard external shock model,with early-time emission dominated by a reverse shock(RS)and a subsequent transition to forward shock(FS)emission.Our afterglow modeling yields a consistent estimate of the initial Lorentz factor(Γ_(0)∼234).Furthermore,the RS-to-FS magnetic field ratio(R 302B)indicates that the RS region is significantly more magnetized than the FS region.An isotropic-equivalent kinetic energy of E_(k,iso)=5.25×10^(54) erg is derived,and the correspondingγ-ray radiation efficiency is estimated to beη_(γ)=3.1%.On the other hand,the standard afterglow model cannot reproduce the X-ray light curve of GRB 240825A,calling for improved models to characterize all multiwavelength data.
基金supported by NSFC grant No.12393852the Yunnan Fundamental Research Project(grant No.202501AS070068).
文摘Supernova remnants(SNRs)interacting with molecular clouds(MCs)are recognized as the sources of γ-rays and cosmic rays in the Galaxy.Based on the SNR-MC system,this study establishes a particle cumulative diffusion model to investigate the mechanism by which high-energy protons escaping from SNRs interact with dense MCs through proton–proton interactions to produce high-energyγ-rays.Using the W51 complex,a typical star-forming region,as a research sample,we analyze the production and propagation characteristics of γ-rays.By employing the Exponential Cutoff Power-Law model and the Markov Chain Monte Carlo method,we fit theγ-ray observational data of W51C,successfully constraining the key physical parameters.Additionally,we systematically search for 1LHAASO sources spatially coincident with SNR-MC systems to explore the potential origins of ultra-high-energy(UHE) γ-ray sources.The results indicate that the radiation characteristics of the UHE γ-ray sources are highly consistent with the SNR-MC systems,further supporting their candidacy as PeVatrons in the Galaxy.
基金supported by the National Natural Science Foundation of China(NSFC,grant Nos.12275279 and 12405124)the China Postdoctoral Science Foundation(No.2023M730423)Horizontal research project in natural sciences(No.H20230120)。
文摘The study of high-energy gamma-ray emission from gamma-ray bursts(GRBs)involves complex synchrotron radiation and synchrotron self-Compton(SSC)scattering mechanisms with multiple parameters exhibiting a wide distribution.Recent advancements in GRB research,particularly the observation of very high energy(VHE,>100 Ge V)radiation,have ushered in a new era of multiwavelength exploration,offering fresh perspectives and limitations for understanding GRB radiation mechanisms.This study aimed to leverage VHE observations to refine constraints on synchrotron+SSC radiation from electrons accelerated by forward shocks.By analyzing two external environments—the uniform interstellar medium and stratified stellar wind medium,we conducted spectral and variability fitting for five specific bursts(GRB 180720B,GRB 190114C,GRB 190829A,GRB 201216C,and GRB 221009A)to identify the optimal parameters characterizing these events.A comparative analysis of model parameter distributions with and without VHE radiation observations reveals that the magnetic energy equipartition factorεBis more concentrated with VHE emissions.This suggests that VHE emissions may offer greater constraints on this microphysical parameter.Additionally,we found that the energy budget between VHE and ke V–Me Vγ-ray emissions under the SSC radiation exhibits an almost linear relationship,which may serve as a tool to differentiate radiation mechanisms.We anticipate future statistical analyses of additional VHE bursts to validate our findings.
文摘We perform a time-resolved statistical study of GRB 221009A’s X-ray emission using Swift XRT Photon Counting and Windowed Timing data.After standard reduction(barycentric correction,pile-up,background subtraction via HEASOFT),we extracted light curves for each observational ID and for their aggregation.Countrate histograms were fitted using various statistical distributions;fit quality was assessed by chi-squared and the Bayesian Information Criterion.The first observational segment is best described by a Gaussian distribution(χ^(2)=68.4;BIC=7651.2),and the second by a Poisson distribution(χ^(2)=33.5;BIC=4413.3).When all segments are combined,the lognormal model provides the superior fit(χ^(2)=541.9;BIC=34365.5),indicating that the full data set’s count rates exhibit the skewness expected from a multiplicative process.These findings demonstrate that while individual time intervals conform to discrete or symmetric statistics,the collective emission profile across multiple observations is better captured by a lognormal distribution,consistent with complex,compounded variability in GRB afterglows.
