The Study Of Anisotropy And Periodic Variation Of Cosmic Rays With The TibetⅢ Air Shower Array

Cosmic rays(CRs)are high energy particles from distant universe.The origin, acceleration and propagation of CRs are fundamental problem in research of CRs. The most of CRs are charged particles,thus cosmic ray(CR)particles lose their original direction and present isotropic because they can be deflected by galactic magnetic field(GMF).CR anisotropy in different energy region has been discovered by some experiments yet.The research of CR anisotropy plays an important role because it has close relationship with the origin,acceleration and propagation of CRs.No reliable theory can interpret the origin of CR anisotropy until now.The below several reasons may result in CR anisotropy:The uneven distribution of CR sources could lead to CR anisotropy;Large scale GMF may also cause the CR anisotropy;CR anisotropy less than GeV energy result from solar magnetic field and interplanetary magnetic field(IMF);An expected CR anisotropy is caused by the relative motion between the observer and the CR plasma.Such anisotropy like Doppler Effect is called Compton-Getting(CG)effect,caused by Earth's orbital motion around sun.Since CR energy spectrum present negative power law from 1 MeV to 10~20eV, different techniques should be applied to detect CRs in different energy regions.In the energy region less than 30GeV,CR flux are higher,space detector play an important role,for instance,satellite and balloon experiment.Higher energy primary cosmic rays produce extensive air showers(EAS),through the indirect methods with the ground-based detectors.Above several hundred GeV space detector's effective area is too small to observe the high energy CRs because of their lower flux.Ground-based experiments are adopted,including Cherenkov Telescope and Air Shower Array and atmospheric fluorescence experiment.Yang Ba Jing ASγexperiment is one of EAS array.ASγexperiment has been located at Yang Ba Jing town,Tibet,China(90.522°E,30.102°N,and 4300 m above sea level)which atmospheric depth are 606g/cm~2.Owing to high altitude,wide viewing field,long effective time and lower energy threshold advantages,ASγexperiment specialize in detecting the CR anisotropy.This work is to study the CR anisotropy research based on the east-west method and the periodic variation of CR anisotropy research using Lomb Scargle Fourier transformation with the TibetⅢarray data.To eliminate meteorological effect and possible instrumental effect we adopted the East-West subtraction method to study primary CR periodic variation.The theory of East-West subtraction method is:The CR events are divieded into two parts(east and west)according to their arrival direction in Horizontal Coordinate.Because earth rotates from west to east,we subtract east and west event rates and normalize the difference by their sum to form the relative intensity difference,and we further divide this relative difference by the hour angle separation to obtain the CR differential intensity.The results of solar and sidereal anisotropy were given in this thesis.The amplitude of solar anisotropy at the 12.0 TeV is about 0.04%.The phase of solar modulation locates at local 6 hour.The results were consistent with expected Compton-Getting(CG)effect.While at lower energy the amplitude and phase of solar modulation deviate from the expected CG effect.The measurement indicates an additional anisotropy superposed on the CG anisotropy.It may be ascribed to solar magnetic modulation.The amplitude of solar modulation decrease with the increasing energy.The amplitude of sidereal anisotropy is about 0.12%.The CRs increase at local 5 hour and the decrease at local 18 hour.The amplitude and phase of sidereal anisotropy show little energy dependence.We further study the periodic variation of CR anisotropy using Lomb Scargle Fourier transformation based on east-west method.Lomb Scargle Fourier transformafion's superiority are subtracting the illusive signal due to uneven data and giving effective probability of different frequency signal,we build up CR differential intensity time series according to east-west method.The Lomb power of CR differential intensity can be obtained by Lomb Scargle Fourier and 50 was given by formula.95%lower limit of Lomb power were given from 1 hour to 2 year by MC simulation.The results show the 95%lower limit is smooth between 1 hour and 90days.But the 95%lower limit which was less than 1hour and more than 90 days began to ascend.Besides solar,sidereal,semi-sidereal diurnal variation,there are no other periodic modulation between 1 hour and 90 days.Sidereal variation can be characterized by the first and second harmonics,while solar variation can be alone described by the first harmonics.There is no periodic variation according to solar activity in lower energy range(4.0TeV).There are three innovative points in our thesis.1):CR anisotropy was analyzed using East-West method with CR events recorded by TibetⅢASγarray during the period from November 1999 to November 2005.The former published results were updated.2):Lomb Scargle Fourier transformation based on east-west method was applied to study periodic variation of CR anisotropy.The method can eliminate the fake signals due to uneven time series and give different frequency probability.3): The thesis gave the 95%lower limit of Lomb power by quick MC simulation.And the deficiency of this thesis is:ASγexperiment data is less than one solar activity period. So periodic modulation of CRs more than 90 days have not been reaserached by now. Long periodic modulation of CRs according to solar activity will be verified by more data.