The Large High Altitude Air Shower Observatory(LHAASO)has three sub-arrays,KM2A,WCDA,and WFCTA.The flux variations of cosmic ray air showers were studied by analyzing the KM2A data during a thunderstorm on June 10,202...The Large High Altitude Air Shower Observatory(LHAASO)has three sub-arrays,KM2A,WCDA,and WFCTA.The flux variations of cosmic ray air showers were studied by analyzing the KM2A data during a thunderstorm on June 10,2021.The number of shower events that meet the trigger conditions increases significantly in atmospheric electric fields,with a maximum fractional increase of 20%.The variations in trigger rates(increases or decreases)were found to be strongly dependent on the primary zenith angle.The flux of secondary particles increased significantly,following a trend similar to that of shower events.To better understand the observed behavior,Monte Carlo simulations were performed with CORSIKA and G4KM2A(a code based on GEANT4).We found that the experimental data(in saturated negative fields)were in good agreement with the simulations,assuming the presence of a uniform electric field of-700 V/cm with a thickness of 1500 m in the atmosphere above the observation level.Due to the acceleration/deceleration by the atmospheric electric field,the number of secondary particles with energy above the detector threshold was modified,resulting in the changes in shower detection rate.展开更多
The first Water Cherenkov detector of the LHAASO experiment(WCDA-1)has been operating since April 2019.The data for the first year have been analyzed to test its performance by observing the Crab Nebula as a standard ...The first Water Cherenkov detector of the LHAASO experiment(WCDA-1)has been operating since April 2019.The data for the first year have been analyzed to test its performance by observing the Crab Nebula as a standard candle.The WCDA-1 achieves a sensitivity of 65 mCU per year,with a statistical threshold of 5 cr.To accomplish this,a 97.7%cosmic-ray background rejection rate around 1 TeV and 99.8%around 6 TeV with an ap proximate photon acceptance of 50%is achieved after applying an algorithm to separate gamma-induced showers.The angular resolution is measured using the Crab Nebula as a point source to be approximately 0.45°at 1 TeV and better than 0.2°above 6 TeV,with a pointing accuracy better than 0.05°.These values all match the design specifications.The energy resolution is found to be 33%for gamma rays around 6 TeV.The spectral energy distribution of the Crab Nebula in the range from 500 GeV to 15.8 TeV is measured and found to be in agreement with the results from other TeV gamma ray observatories.展开更多
The observation of short gamma ray bursts(SGRBs)in the TeV energy range plays an important role in understanding the radiation mechanism and probing potential new physics,such as Lorentz invariance violation(LIV).Howe...The observation of short gamma ray bursts(SGRBs)in the TeV energy range plays an important role in understanding the radiation mechanism and probing potential new physics,such as Lorentz invariance violation(LIV).However,no SGRBs have been observed in this energy range owing to the short duration of SGRBs and the weakness of current experiments.New experiments with new technology are required to detect the very high energy(VHE)emission of SGRBs.In this study,we simulate the VHE γ-ray emissions from SGRBs and calculate the annu-al detection rate with the High Altitude Detection of Astronomical Radiation(HADAR)experiment.First,a set of pseudo-SGRB samples is generated and checked using the observations of the Fermi-GBM,Fermi-LAT,and Swift-BAT measurements.The annual detection rate is calculated from these SGRB samples based on the performance of the HADAR instrument.As a result,the HADAR experiment can detect 0.5 SGRBs per year if the spectral break-off of γ-rays caused by the internal absorption and Klein-Nishina(KN)effect is larger than 100 GeV.For a GRB090510-like GRB in HADAR's view,it should be possible to detect approximately 2000 photons considering the internal absorption and KN effect.With a time delay assumption due to LIV effects,a simulated light curve of GRB090510 has evident energy dependence.We hope that the HADAR experiment can perform SGRB observa-tions and test our calculations in the future.展开更多
The muonic component of the extensive air showers (EAS) is of great importance for the astroparticle physics. It carries the information about the properties of primary cosmic ray (CR) particles, such as their mass, a...The muonic component of the extensive air showers (EAS) is of great importance for the astroparticle physics. It carries the information about the properties of primary cosmic ray (CR) particles, such as their mass, and electromagnetic and hadronic nature. It provides a sensitive test for the hadronic interaction models, which are inevitable for describing the cascade shower development of cosmic rays in EAS experiments. The YangBaJing Hybrid Array (YBJ-HA) experiment has been in operation since the end of 2016. Surface detectors are used for the measurements of primary energy, angular direction and core position of a shower event, while underground muon detectors are used for measuring the density of muons at various locations. Using the data obtained by the YBJ-HA experiment,this work reports the first measurement of the lateral muon distribution for the primary cosmic ray energy in the 100TeV region. The punch-through effect is evaluated via MC simulation.展开更多
The Water Cherenkov Detector Array(WCDA) is a major component of the Large High Altitude Air Shower Array Observatory(LHAASO), a new generation cosmic-ray experiment with unprecedented sensitivity, currently under con...The Water Cherenkov Detector Array(WCDA) is a major component of the Large High Altitude Air Shower Array Observatory(LHAASO), a new generation cosmic-ray experiment with unprecedented sensitivity, currently under construction. WCDA is aimed at the study of TeV γ-rays. In order to evaluate the prospects of searching for TeV γ-ray sources with WCDA, we present a projection of the one-year sensitivity of WCDA to TeV γ-ray sources from TeVCat using an all-sky approach. Out of 128 TeVCat sources observable by WCDA up to a zenith angle of 45°, we estimate that 42 would be detectable in one year of observations at a median energy of 1 TeV. Most of them are Galactic sources, and the extragalactic sources are Active Galactic Nuclei(AGN).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 in China by National Key R&D program of China(2018YFA0404201,2018YFA0404202,2018YFA0404203,2018YFA0404204)NSFC(U2031101,11475141,12147208)in Thailand by RTA6280002 from Thailand Science Research and Innovation。
文摘The Large High Altitude Air Shower Observatory(LHAASO)has three sub-arrays,KM2A,WCDA,and WFCTA.The flux variations of cosmic ray air showers were studied by analyzing the KM2A data during a thunderstorm on June 10,2021.The number of shower events that meet the trigger conditions increases significantly in atmospheric electric fields,with a maximum fractional increase of 20%.The variations in trigger rates(increases or decreases)were found to be strongly dependent on the primary zenith angle.The flux of secondary particles increased significantly,following a trend similar to that of shower events.To better understand the observed behavior,Monte Carlo simulations were performed with CORSIKA and G4KM2A(a code based on GEANT4).We found that the experimental data(in saturated negative fields)were in good agreement with the simulations,assuming the presence of a uniform electric field of-700 V/cm with a thickness of 1500 m in the atmosphere above the observation level.Due to the acceleration/deceleration by the atmospheric electric field,the number of secondary particles with energy above the detector threshold was modified,resulting in the changes in shower detection rate.
基金Supported by the following grants:the National Key R&D program of China(2018YFA0404201,2018YFA0404202,2018YFA0404203)the National Natural Science Foundation of China(12022502,11905227,U1931112,11635011,11761141001,Y811A35,11675187,U1831208,U1931111)in Thailand by RTA6280002 from Thailand Science Research and Innovation。
文摘The first Water Cherenkov detector of the LHAASO experiment(WCDA-1)has been operating since April 2019.The data for the first year have been analyzed to test its performance by observing the Crab Nebula as a standard candle.The WCDA-1 achieves a sensitivity of 65 mCU per year,with a statistical threshold of 5 cr.To accomplish this,a 97.7%cosmic-ray background rejection rate around 1 TeV and 99.8%around 6 TeV with an ap proximate photon acceptance of 50%is achieved after applying an algorithm to separate gamma-induced showers.The angular resolution is measured using the Crab Nebula as a point source to be approximately 0.45°at 1 TeV and better than 0.2°above 6 TeV,with a pointing accuracy better than 0.05°.These values all match the design specifications.The energy resolution is found to be 33%for gamma rays around 6 TeV.The spectral energy distribution of the Crab Nebula in the range from 500 GeV to 15.8 TeV is measured and found to be in agreement with the results from other TeV gamma ray observatories.
基金Supported by the National Natural Science Foundation of China(12263004,12263005,12275279)。
文摘The observation of short gamma ray bursts(SGRBs)in the TeV energy range plays an important role in understanding the radiation mechanism and probing potential new physics,such as Lorentz invariance violation(LIV).However,no SGRBs have been observed in this energy range owing to the short duration of SGRBs and the weakness of current experiments.New experiments with new technology are required to detect the very high energy(VHE)emission of SGRBs.In this study,we simulate the VHE γ-ray emissions from SGRBs and calculate the annu-al detection rate with the High Altitude Detection of Astronomical Radiation(HADAR)experiment.First,a set of pseudo-SGRB samples is generated and checked using the observations of the Fermi-GBM,Fermi-LAT,and Swift-BAT measurements.The annual detection rate is calculated from these SGRB samples based on the performance of the HADAR instrument.As a result,the HADAR experiment can detect 0.5 SGRBs per year if the spectral break-off of γ-rays caused by the internal absorption and Klein-Nishina(KN)effect is larger than 100 GeV.For a GRB090510-like GRB in HADAR's view,it should be possible to detect approximately 2000 photons considering the internal absorption and KN effect.With a time delay assumption due to LIV effects,a simulated light curve of GRB090510 has evident energy dependence.We hope that the HADAR experiment can perform SGRB observa-tions and test our calculations in the future.
文摘HADAR(High Altitude Detection of Astronomical Radiation)是一个基于大气切伦科夫成像技术的地面望远镜阵列,其采用大口径折射式水透镜系统来收集大气切伦科夫光,以实现对10 GeV—10 TeV能量段的伽马射线和宇宙线的探测.HADAR具有低阈能和大视场的优势,因此可以对天区进行连续扫描和观测,在观测活动星系核(Active Galactic Nuclei,AGN)等银河系外伽马射线源方面具有明显优势.本文研究了HADAR实验对AGN的探测能力.基于费米望远镜(Fermi Large Area Telescope,Fermi-LAT)的AGN源能谱信息,将观测能量外推至甚高能能段,同时加入河外背景光的吸收效应,以计算HADAR对AGN源观测的统计显著性.研究结果显示,HADAR运行一年时间,预计将有31个Fermi-LAT AGN源以高于5倍显著性被观测到,其中大部分为蝎虎状天体类型.
基金Supported by National Key R&D Program of China(2018YFA0404202)National Natural Science Foundation of China(11635011,11761141001,11765019,11775233)
文摘The muonic component of the extensive air showers (EAS) is of great importance for the astroparticle physics. It carries the information about the properties of primary cosmic ray (CR) particles, such as their mass, and electromagnetic and hadronic nature. It provides a sensitive test for the hadronic interaction models, which are inevitable for describing the cascade shower development of cosmic rays in EAS experiments. The YangBaJing Hybrid Array (YBJ-HA) experiment has been in operation since the end of 2016. Surface detectors are used for the measurements of primary energy, angular direction and core position of a shower event, while underground muon detectors are used for measuring the density of muons at various locations. Using the data obtained by the YBJ-HA experiment,this work reports the first measurement of the lateral muon distribution for the primary cosmic ray energy in the 100TeV region. The punch-through effect is evaluated via MC simulation.
基金Supported by National Natural Science Foundation of China(11761141001,11635011,11873005)The LHAASO project is supported by the National Key R&D Program of China(2018YFA0404200),the Chinese Academy of Sciences,the Key Laboratory of Particle Astrophysics,IHEP,CAS。
文摘The Water Cherenkov Detector Array(WCDA) is a major component of the Large High Altitude Air Shower Array Observatory(LHAASO), a new generation cosmic-ray experiment with unprecedented sensitivity, currently under construction. WCDA is aimed at the study of TeV γ-rays. In order to evaluate the prospects of searching for TeV γ-ray sources with WCDA, we present a projection of the one-year sensitivity of WCDA to TeV γ-ray sources from TeVCat using an all-sky approach. Out of 128 TeVCat sources observable by WCDA up to a zenith angle of 45°, we estimate that 42 would be detectable in one year of observations at a median energy of 1 TeV. Most of them are Galactic sources, and the extragalactic sources are Active Galactic Nuclei(AGN).
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.
