Studying gamma-ray pulsars with fermi large area telescope

Abstract

Pulsars are extremely powerful emitters in the universe. They are also major sources of cosmic gamma-ray radiations. The Fermi Large Area Telescope, launched in 2008, is currently the largest gamma-ray space observatory in the world. Now, the spacecraft has already accumulated almost 10 years of data from the sky-survey operation every day. This provides huge resources for studying the high energy phenomena of gamma-ray pulsars. In this thesis, we will present two independent researches using the Fermi data. The first study is on an individual compact pulsar binary system, 3FGL J2039.6-5618. We performed timing analyses as well as spectral analyses for a deep understanding in the emission mechanisms of this target. We found evidence on the orbital modulation with an orbital period of ~5.4 hours in the gamma-ray band. We also observed that this modulation produces an extra component in the energy range of 0.1-3 GeV. Using model simulations, we explained this extra component by the inverse Compton scattering between the pulsar wind and the stellar wind. The second study is on a group of high energy pulsars. With the advanced sensitivity of the Fermi, the number of pulsars with pulsations detected above 10 GeV is increasing. We will present two approaches to explain the production of these very high energy photons: the non-stationary outer gap model and the inverse Compton model. The former model describes the superposition of different stationary outer gap emissions under different current injection rates. When the pulsar is at a low injection rate, the outer gap is expanded to emit higher energy gamma-rays. The latter model uses the inverse Compton scattering between the accelerated particles and background soft photons to achieve high energy emissions. Then, we used these models to simulate the gamma-ray spectra of 53 high energy pulsars listed in the Fermi Third High Energy Source Catalog.