Application of deep learning methods combined with physical background in wide field of view imaging atmospheric Cherenkov telescopes

The High Altitude Detection of Astronomical Radiation(HADAR)experiment,which was constructed in Tibet,China,combines the wide-angle advantages of traditional EAS array detectors with the high-sensitivity advantages of focused Cherenkov detectors.Its objective is to observe transient sources such as gamma-ray bursts and the counterparts of gravitational waves.This study aims to utilize the latest AI technology to enhance the sensitivity of HADAR experiments.Training datasets and models with distinctive creativity were constructed by incorporating the relevant physical theories for various applications.These models can determine the type,energy,and direction of the incident particles after careful design.We obtained a background identification accuracy of 98.6%,a relative energy reconstruction error of 10.0%,and an angular resolution of 0.22°in a test dataset at 10 TeV.These findings demonstrate the significant potential for enhancing the precision and dependability of detector data analysis in astrophysical research.By using deep learning techniques,the HADAR experiment’s observational sensitivity to the Crab Nebula has surpassed that of MAGIC and H.E.S.S.at energies below 0.5 TeV and remains competitive with conventional narrow-field Cherenkov telescopes at higher energies.In addition,our experiment offers a new approach for dealing with strongly connected,scattered data.

Prospects for the detection rate of very-high-energyγ-ray emissions from shortγ-ray bursts with the HADAR experiment

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.

Lateral distribution of EAS muons measured for the primary cosmic ray energy around 100 TeV

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.

Nearby source interpretation of differences among light and medium composition spectra in cosmic rays

Recently the AMS-02 reported the precise measurements of the energy spectra of medium-mass compositions(Neon,Magnesium,Silicon)of primary cosmic rays,which reveal different properties from those of light compositions(Helium,Carbon,Oxygen).Here we propose a nearby source scenario,together with the background source contribution,to explain the newly measured spectra of cosmic ray Ne,Mg,Si,and particularly their differences from that of He,C,O.Their differences at high energies can be naturally accounted for by the element abundance of the nearby source.Specifically,the abundance ratio of the nearby source to the background of the Ne,Mg,Si elements is lower by a factor of~1.7 than that of the He,C,O elements.Such a diference could be due to the abundance difference of the stellar evolution of the progenitor star or the acceleration process/environment,of the nearby source.This scenario can simultaneously explain the high-energy spectral softening features of cos-mic ray spectra revealed recently by CREAM/NUCLEON/DAMPE,as well as the energy-dependent behaviors of the large scale anisotropies.It is predicted that the dipole anisotropy amplitudes below PeV energies of the Ne,Mg,Si group are smaller than that of the He,C,O group,which can be tested with future measurements.

Galactic cosmic ray propagation: sub-PeV diffuse gamma-ray and neutrino emission

The Tibet ASγexperiment just reported their measurement of sub-PeV diffuse gamma-ray emission from the Galactic disk,with the highest energy up to 957 TeV.These diffuse gamma rays are most likely the hadronic origin by cosmic ray(CR)interaction with interstellar gas in the galaxy.This measurement provides direct evidence to the hypothesis that the Galactic Cosmic Rays(GCRs)can be accelerated beyond PeV energies.In this work,we try to explain the sub-PeV diffuse gamma-ray spectrum with different CR propagation models.We find that there is a tension between the sub-PeV diffuse gamma-ray and the local CR spectrum.To describe the sub-PeV diffuse gamma-ray flux,it generally requires larger local CR flux than measurement in the knee region.We further calculate the PeV neutrino flux from the CR propagation model.Even all of these sub-PeV diffuse gamma rays originate from the propagation,the Galactic Neutrinos(GNs)only account for less than∼15%of observed flux,most of which are still from extragalactic sources.

Galactic cosmic ray propagation: sub-PeV diffuse gamma-ray and neutrino emission

The Tibet ASγexperiment just reported their measurement of sub-PeV diffuse gamma-ray emission from the Galactic disk,with the highest energy up to 957 TeV.These diffuse gamma rays are most likely the hadronic origin by cosmic ray(CR)interaction with interstellar gas in the galaxy.This measurement provides direct evidence to the hypothesis that the Galactic Cosmic Rays(GCRs)can be accelerated beyond PeV energies.In this work,we try to explain the sub-PeV diffuse gamma-ray spectrum with different CR propagation models.We find that there is a tension between the sub-PeV diffuse gamma-ray and the local CR spectrum.To describe the sub-PeV diffuse gamma-ray flux,it generally requires larger local CR flux than measurement in the knee region.We further calculate the PeV neutrino flux from the CR propagation model.Even all of these sub-PeV diffuse gamma rays originate from the propagation,the Galactic Neutrinos(GNs)only account for less than~15%of observed flux,most of which are still from extragalactic sources.

Constraining the cosmic ray propagation halo thickness using Fermi-LAT observations of high-latitude clouds

The diffusive halo is a basic characteristic of cosmic ray(CR)propagation and can advance our understanding of many CR-related phenomena and indirect dark matter.The method used to derive the halo size often has degeneracy problems and is thus affected by large uncertainties.The diffuseγrays from high-latitude clouds might shed light on the halo size independently.Because predictions using the spatially dependent propagation(SDP)model have better agreement with the observed CRs than those of the conventional propagation model,in this work,we investigated halo thickness based on the SDP model using Fermi-LATγ-ray observations of high-and intermediatevelocity clouds.We found that to avoid exceeding the relativeγ-ray emissivity in high-latitude clouds,the halo thickness should be in the range of 3.3-9 kpc.Moreover,the spatial morphology ofγ-rays estimated based on the SDP model for different values of the halo thickness are distinctive,which provides us with a tool to determine the halo size.This newly developed model can be tested and tuned using multi-wavelength observations in future studies.

100 TeV diffuse γ-rays observation by YangBaJing Hybrid Array

Purpose Cosmic rays up to PeV energy are believed to be generated in our galaxy.γ-rays at 100TeV energies are important probe to identify PeVtrons.Besides,γ-rays contain additional information on the propagation of the galactic cosmic rays.Methods Diffuseγ-rays originating from the Galactic plane from 20 to 200 TeV region are studied with early 160-day data collected by YangBaJing Hybrid Array(YBJ-HA),which is a hybrid array and consists of scintillation detectors and underground muon detectors.All-distance equi-zenith angle and time-swapping methods are used to analyze the number ofγ-rays excess.Result and conclusion Because of no significant observation onγ-ray emission,Helene's method is adopted to derive the 90%confidence level upper limits on the flux of diffuse galacticγ-rays.And the limit to the ratio of the flux ofγ-rays to CRs is obtained at the order of 10^(-4),which is the current best result at these energies.