Radiative energy losses are very important in regulating the cosmic ray electron and/or positron(CRE) spectrum during their propagation in the Milky Way. Particularly, the Klein–Nishina(KN) effect of the inverse Comp...Radiative energy losses are very important in regulating the cosmic ray electron and/or positron(CRE) spectrum during their propagation in the Milky Way. Particularly, the Klein–Nishina(KN) effect of the inverse Compton scattering(ICS) results in less efficient energy losses of high-energy electrons, which is expected to leave imprints on the propagated electron spectrum. It has been proposed that the hardening of CRE spectra around 50 GeV observed by Fermi-LAT, AMS-02, and DAMPE could be due to the KN effect. We show in this work that the transition from the Thomson regime to the KN regime of the ICS is actually quite smooth compared with the approximate treatment adopted in some previous works. As a result, the observed spectral hardening of CREs cannot be explained by the KN effect. It means that an additional hardening of the primary electrons spectrum is needed. We also provide a parameterized form for the accurate calculation of the ICS energy-loss rate in a wide energy range.展开更多
The recently discovered satellite dwarf galaxy Ursa Major III provides a promising opportunity to explore the signatures resulting from dark matter(DM)annihilation owing to its proximity and large J-factor.Given the a...The recently discovered satellite dwarf galaxy Ursa Major III provides a promising opportunity to explore the signatures resulting from dark matter(DM)annihilation owing to its proximity and large J-factor.Given the absence of an excess ofγ-ray signatures originating from Ursa Major III,observations ofγ-rays,such as those from Fermi-LAT,can be utilized to set constraints on the DM annihilation cross-section.In this study,we determined the DM density profile and considered the relationship between DM density and velocity dispersion at different locations within Ursa Major III through Jeans analysis.We calculated the J-factor of Ursa Major III for s-wave annihilation along with the effective J-factors for p-wave and Sommerfeld enhanced annihilation scenarios.Employing these derived J-factors,we set stringent constraints on DM annihilation cross-sections in three scenarios.Given the substantial impact of member star identification on the J-factor of Ursa Major III,we further calculated J-factors under the exclusion of the largest velocity outlier.Our analysis reveals a notable reduction in the median value and an increase in the deviation of J-factors,thereby leading to considerably weaker constraints.展开更多
Numerous simulations indicate that a large number of subhalos should be hosted by the Milky Way.The potential existence of a nearby subhalo could have important implications for our understanding of dark matter(DM)ann...Numerous simulations indicate that a large number of subhalos should be hosted by the Milky Way.The potential existence of a nearby subhalo could have important implications for our understanding of dark matter(DM)annihilation.In this study,we investigate the hypothetical presence of a nearby subhalo and set the upper limits on the DM annihilation cross section by analyzing the cosmic-ray antiproton spectrum.By presenting the ratios of annihilation cross section limits for scenarios with and without a nearby subhalo,we can quantitatively evaluate the potential impact of the nearby subhalo on the limits of the DM annihilation cross section.The impacts of the concentration model and the subhalo probability distribution have been considered.We explore the antiproton contribution of the potential nearby DM subhalo accounting for the DAMPE e+spectrum at~1.4 TeV and find that the current AMS-02 antiproton results do not limit this contribution.展开更多
The full array of the Large High Altitude Air Shower Observatory(LHAASO)has been in operation since July 2021.For its kilometer-square array(KM2A),we optimized the selection criteria for very high and ultrahigh energy...The full array of the Large High Altitude Air Shower Observatory(LHAASO)has been in operation since July 2021.For its kilometer-square array(KM2A),we optimized the selection criteria for very high and ultrahigh energyγ-rays using data collected from August 2021 to August 2022,resulting in an improvement in significance of the detection in the Crab Nebula of approximately 15%,compared with that of previous cuts.With the implementation of these new selection criteria,the angular resolution was also significantly improved by approximately 10%at tens of TeV.Other aspects of the full KM2A array performance,such as the pointing error,were also calibrated using the Crab Nebula.The resulting energy spectrum of the Crab Nebula in the energy range of 10-1000 TeV are well fitted by a log-parabola model,which is consistent with the previous results from LHAASO and other experiments.展开更多
基金Supported by the National Key Research and Development Program of China(Grant No.2016YFA0400203 and 2016YFA0400204)the National Natural Science Foundation of China(Grant Nos.11722328,U1738205,U1738203,11851303 and 11851305)the Program for Innovative Talents and Entrepreneur in Jiangsu。
文摘Radiative energy losses are very important in regulating the cosmic ray electron and/or positron(CRE) spectrum during their propagation in the Milky Way. Particularly, the Klein–Nishina(KN) effect of the inverse Compton scattering(ICS) results in less efficient energy losses of high-energy electrons, which is expected to leave imprints on the propagated electron spectrum. It has been proposed that the hardening of CRE spectra around 50 GeV observed by Fermi-LAT, AMS-02, and DAMPE could be due to the KN effect. We show in this work that the transition from the Thomson regime to the KN regime of the ICS is actually quite smooth compared with the approximate treatment adopted in some previous works. As a result, the observed spectral hardening of CREs cannot be explained by the KN effect. It means that an additional hardening of the primary electrons spectrum is needed. We also provide a parameterized form for the accurate calculation of the ICS energy-loss rate in a wide energy range.
基金Supported by the National Natural Science Foundation of China (11947005,12175248,12205388,12227804)the Science&Technology Development Fund of Tianjin Education Commission for Higher Education (2020KJ003)the PhD Research Startup Foundation of Tianjin Normal University (52XB1912)。
文摘The recently discovered satellite dwarf galaxy Ursa Major III provides a promising opportunity to explore the signatures resulting from dark matter(DM)annihilation owing to its proximity and large J-factor.Given the absence of an excess ofγ-ray signatures originating from Ursa Major III,observations ofγ-rays,such as those from Fermi-LAT,can be utilized to set constraints on the DM annihilation cross-section.In this study,we determined the DM density profile and considered the relationship between DM density and velocity dispersion at different locations within Ursa Major III through Jeans analysis.We calculated the J-factor of Ursa Major III for s-wave annihilation along with the effective J-factors for p-wave and Sommerfeld enhanced annihilation scenarios.Employing these derived J-factors,we set stringent constraints on DM annihilation cross-sections in three scenarios.Given the substantial impact of member star identification on the J-factor of Ursa Major III,we further calculated J-factors under the exclusion of the largest velocity outlier.Our analysis reveals a notable reduction in the median value and an increase in the deviation of J-factors,thereby leading to considerably weaker constraints.
基金Supported by the Science&Technology Development Fund of Tianjin Education Commission for Higher Education(2020KJ003)。
文摘Numerous simulations indicate that a large number of subhalos should be hosted by the Milky Way.The potential existence of a nearby subhalo could have important implications for our understanding of dark matter(DM)annihilation.In this study,we investigate the hypothetical presence of a nearby subhalo and set the upper limits on the DM annihilation cross section by analyzing the cosmic-ray antiproton spectrum.By presenting the ratios of annihilation cross section limits for scenarios with and without a nearby subhalo,we can quantitatively evaluate the potential impact of the nearby subhalo on the limits of the DM annihilation cross section.The impacts of the concentration model and the subhalo probability distribution have been considered.We explore the antiproton contribution of the potential nearby DM subhalo accounting for the DAMPE e+spectrum at~1.4 TeV and find that the current AMS-02 antiproton results do not limit this contribution.
基金Supported by the National Key R&D Program of China(2018YFA0404201,2018YFA0404202,2018YFA0404203,2018YFA0404204)the National Natural Science Foundation of China(12022502,12205314,12105301,12261160362,12105294,U1931201)+2 种基金the Youth Innovation Promotion Association CAS(2022010)in Thailand by the National Science and Technology Development Agency(NSTDA)the National Research Council of Thailand(NRCT):High-Potential Research Team Grant Program(N42A650868)。
文摘The full array of the Large High Altitude Air Shower Observatory(LHAASO)has been in operation since July 2021.For its kilometer-square array(KM2A),we optimized the selection criteria for very high and ultrahigh energyγ-rays using data collected from August 2021 to August 2022,resulting in an improvement in significance of the detection in the Crab Nebula of approximately 15%,compared with that of previous cuts.With the implementation of these new selection criteria,the angular resolution was also significantly improved by approximately 10%at tens of TeV.Other aspects of the full KM2A array performance,such as the pointing error,were also calibrated using the Crab Nebula.The resulting energy spectrum of the Crab Nebula in the energy range of 10-1000 TeV are well fitted by a log-parabola model,which is consistent with the previous results from LHAASO and other experiments.
