Study Of The Solar And The Solar-terrestrial Space Magnetic Fields Using The Cosmic-ray Sun Shadow Of The Lhaaso Experiment

LHAASO is located in Haizishan,Daocheng County,Sichuan Province at an altitude of 4410m.It is a new generation of the composite cosmic ray detector array,which is composed of one square kilometer array(KM2A),water Cerenkov detector array(WCDA)and wide-angle Cerenkov telescope array(WFCTA).LHAASO is the largest and most sensitive cosmic-ray and gamma-ray detection device in the 100GeV to 100PeV energy region in the world.One of its important scientific objectives is to study the solarterrestrial space environment.During the propagation of cosmic rays to the earth,they are blocked by the Sun,resulting in the loss of the flux in the direction of the Sun and the formation of the Sun shadow.Cosmic rays are mainly positively charged nuclei,which are deflected by the coronal magnetic field,interplanetary magnetic field and geomagnetic field during solar-terrestrial space flight,resulting in the displacement,extension and deficit of Sun shadow.LHAASO experiment has the characteristics of a wide field of view,high duty cycle and wide energy range,and has high observation sensitivity to Sun shadow.Therefore,based on the observation of these characteristics of Sun shadow by LHAASO,the solar-terrestrial magnetic field can be studied.LHAASO began construction in early 2018 and was completed in July 2021.During this period,the mode of construction and operation was adopted.At the initial stage of the operation of part KM2A,this paper studies and determines the time calibration scheme of KM2A based on the simulated data,and completes the time calibration of part arrays.In the meantime,the method of inspection of detector coordinates is proposed,and several detector coordinate errors are found.These works effectively ensure the reconstruction of KM2A data.In this paper,the change of angular resolution of KM2A with energy is tested by the chessboard method,and the change of pointing accuracy of KM2A with zenith angle and declination,and the change of angular resolution and Moon shadow position with energy are studied in detail through Moon shadow observation.This work provides an important guarantee for the quality of KM2A reconstructed data.This paper also uses the data of the No.1 pool of WCDA to monitor the Moon shadow and gives the pointing accuracy,angular resolution,the variation relationship of Moon shadow position with energy and the stability with time.The influence of the geomagnetic field on the position of the Moon shadow is studied by Moon shadow simulation,which lays a foundation for the calibration of cosmic ray absolute energy.These basic research work on KM2A and WCDA not only ensures the data quality of LHAASO but also lays an important foundation for further Sun shadow research in this paper.For the coronal magnetic field,the Sun shadow can help solve two unsolved problems:one is the uncertainty of the position of the source surface with solar activity in the classical model potential field source surface model(PFSS),and the other is which model of PFSS model and current sheet source surface model(CSSS)is more consistent with the real coronal magnetic field.This paper simulates the Sun shadow with different energy at different stages of the solar cycle 24 and explores the relationship between the deficit ratio and expansion degree of the Sun shadow and the coronal magnetic field model and its parameters.Based on this,it is found that the deficit ratio of Sun shadow with ltev-10tev energy can be used to diagnose the position of the source surface of the PFSS model and some special magnetic field structures of the corona in solar minimum.The extension of Sun shadow with energy below 10TeV can also be used to indirectly diagnose the source surface position of the PFSS model in solar minimum and maximum.The deficit ratio and expansion of Sun shadow with an energy range of ltev to 10TeV can be used to check the coronal magnetic field described by the PFSS model and CSSS model,and even the open magnetic lines at the two poles of the sun.For the interplanetary magnetic field,the Sun shadow can be used to measure the magnetic field intensity and structure in different solar activity periods,and monitor the sudden change of the interplanetary magnetic field,to provide important information for the prediction of space weather which is in the initial stage of the research.Based on the data of the No.1 pool of WCDA,this paper analyzes the Sun shadow every three days from July 26 to August 22,2019.The results show that LHAASO can detect the Sun shadow with high significance in a short time and monitor its position change.Combined with precise Sun shadow simulation,this paper measures the Y component of the interplanetary magnetic field in a short period for the first time,and the measurement results are consistent with the monitoring results of orbiting satellites near the earth,It is verified that LHAASO’s observation of the Sun shadow can monitor the intensity,structure and the sudden change of interplanetary magnetic field.Based on this,this paper also discusses the images of the sector structure of the interplanetary magnetic field and the potential space weather prediction ability of LHAASO’s Sun shadow monitoring.