The Observation Of GRB Based On LHAASO-WCDA Experiment And Study Of Cosmic Ray Propagation

The main contents of this paper include two parts:1.The prospection of an-nual detection rate and search for very-high-energy gamma emission of GRBs based on LHAASO-WCDA experiment;2.The study of the spatially-dependent propagation of galactic cosmic ray.The ?-ray bursts(GRBs)are the most violent explosion events in the universe after the big bang,which can be used as a high-redshift probe to study cosmology.In particular,the observation on the GeV emission of GRB has had fruitful application,such as measuring the extra-galactic background light and strictly constraining on the Lorentz Invariance Violation effect and so on.At present,most of the GRBs are directly observed by the space satellites.Due to the limitted detector area and observation duty,the space-borne experiments are very difficult to observe the gamma emission of GRBs at hundreds of GeV energy region.However,ground-based array experiments,with large effective area,low threshold,wide field of view and high duty cycle,can indirectly speculate the information of primary gamma-rays through reconstructing the direction?energy and core of the secondary particles which are produced by primary particles interacting with air shower.They have considerable advantages in detecting very-high-energy GRBs.WCDA experiment,as an important part of LHAASO experiment,will have the potential to detect GRBs at hundreds of GeV energy region,providing data support for theoretical research of GRB.We study the annual detection rate of high energy GRBs of WCDA experiment by a parametric simulation method.Firstly,on the base of GRBs' energy spectrum and redshift distribution observed by Fermi experiment,a sample of GRBs has been gener-ated.Secondly,we extrapolate their energy spectrum to high energy taking into account the EBL absorption effect and the effective area of WCDA,then all the parameters of each GRB in the sample can be obtained.Finally,with an assumption that the extra high-energy component accounts for 10%of the total luminosity,we find that WCDA has an average GRB detection rate of?1 per year.After predicting the annual detection rate of GRB from the theoretical perspective,we perform the search for very-high-energy gamma ray emission of GRB based on LHAASO-WCDA experiment.Due to data quality directly influences the searching of high energy GRBs,we firstly use the data of single particle model(1 pool)to monitor the time-dependent of some quantities,including rate?charge of anode and dynode?the peak position of 3 peaks in the single particle spectrum,continuously.The long-term stable change of these qualities suggest that the operation of WCDA was stable and the quality of acquired data was good.On this basis,we selecte GRBs located in the WCDA field of view from June to November 2019,with their zenith Angle less than 40° and fluence greater than 1 × 10-6 erg·cm-2.According to the explosion position provided by space satellite experiment,we calculate their significance by mean of the method of equal zenith angle.The significance of these GRBs are all less than 5 from the results of two-dimensional sky map,and no obvious signal exceeded is found.Afterwards the Helene approximation method is used to estimate the flux upper limit of these GRBs.So far,the origin?acceleration and propagation of cosmic ray remain a mystery.Standard propagation model can successfully explain the observed power-law spectrum of cosmic ray,the ratio of secondary to primary particles and distribution of dispersion gamma rays,etc.With the improvement of instrument precision,the observations of cosmic ray energy spectrum and large-scale anisotropy gradually extend to the high en-ergy,their structures are becoming more and more complicated,such as,the spectral hardenings of cosmic ray nuclei above?200 GV followed by softenings around 10 TV,the knee of the all-particle spectrum around PeV energies,as well as the pattern change of the amplitude and phase of the large-scale anisotropies around 100 TeV,etc.These new observations challenge the traditional propagation model.Based on the spatially-dependent plus adjacent source model,we study the energy spectra and anisotropies of different cosmic ray components and find that the expected results of the model could well explain the complex structure of energy spectra of different cosmic ray nuclear and the inversion of amplitude and phase of the anisotropy around 100 TeV,suggesting that they may have a common origin.After that,we also study the dependency between anisotropy and the vertical position of sun.Through analyzing the relationship between the ratio of anisotropic vertical component to radial component and the galaxy outer halo thickness,inner halo thickness,disk thickness and the size of the sun's position vertical component respectively,we find that properly increasing the thickness of the inner halo can effectively suppress vertical anisotropy component,making the model expected results of the anisotropy fit the observation better.It shows that the inner halo thickness of our model is large.In addition,we can determine the sun position above the galaxy disk according to the fitting result between the experimental data and the expec-tation based on the spatially-dependent plus adjacent source model.We also explore the potential anomalous diffusion of cosmic rays via detailed study of 1-dimensional fractal Brownian motions.