Fermi-LAT Gamma-ray Data Analysis And Mode Change Of Transition Pulsars

With the launch and operation of Fermi Gamma-ray Space Telescope,we can obtain information of high energy gamma-ray emission in space.Since the first pulsar was detected in 1967,more than 2000 pulsars have been known.This advances the understanding of the physics of pulsars.Pulsars are one of major gamma-ray source in the Milkey Way.If we know the pulsars better,it can help science of high-energy astrophysics.This thesis mianly forcus on questions of high-energy emission from the pulsar with Fermi LAT gamma-ray data analysis and theoretical interpretation.My thesis firstly introduces the background of pulsars,which contain history,basic character of each type of pulsars.In particular,I emphasize to describe millisecond pulsars,gamma-ray and “glitch” event.Also,I introduce the three emission models: Polar cap model,Outer gap model,slot gap model,as well as high energy gamma-ray emissions process.Second,this thsis introduces Fermi LAT observations for the pulsars,which is the main work during postgraduate.The first two chapters are my learning and understanding about basic knowledge of pulsars and Fermi LAT gamma-ray data analysis which help me completing my work.Then? introduce some of my works during postgraduate.The third chapter is my first work,which mainly introduces the change in the gamma-ray flux and timing parameter on the “glitch” event of PSR J2021+4026.This research obtains the gamma-ray flux variability,the phase-averaged spectra,the phase-resolved spectra and pulse profile of PSR J2021+4026 on the “glitch” event,with using ~8 years Fermi-LAT data.The long-time monitoring of timing parameter provides us a hint to understand the process of the mode change.Combining the timing analysis and spectral analysis,we confirm that a glitch of the pulsar occurred near 2011 October 16,and after the pulsar stay the low-flux stage for 3 years,the flux was returned to the level before the glich with a time scale of a month around 2014 December 10.We suggest this another jump of the gamma-ray flux was not second glitch,but a relaxlation process of the pulsar sates.Through theoretical analysis,we argue two possibilities: one is that the glitch changed the inclination angle of the dipole axis,the other is that the glitch changed the local magnetic field structure around the polar cap.The fourth chapter is about the switching process of millisecond pulsar PSR J1023+0038 between rotaiton powered stage and accretion powered stage.Through Fermi-LAT data analysis,we detect the gamma-ray flux doesn't change after MSP PSR J1023+0038 was switching from rotation powered stage to accretion stage in 2013 June.We confirm the rotation powered stage has been continuted until now.The last chapter is the search for a gamma-ray flux change at several unassociated gamma-ray sources in the Fermi catalog as promising MSP candidates.Based on their gamma-ray flux properties,I pick up five candidates:2FGL J1625.2-0020?2FGL J1653.6-0159?2FGL J1729.5-0854?2FGL J1744.1-7620?2FGL J1946.4-5402.No flux changes from those sources have been detected.Finally,? summarize my works during postgraduate,and present several problems about pulsars to be solved and some prospects for further research.