Study Of Gamma-ray Emission Properties Of Pulsars:Based On Fermi-LAT Observation

Gamma-ray pulsars are very important sources of gamma rays in the universe.Fermi's operation led to a huge increase in the sample size of gamma-ray pulsars.Many models,such as the outer gap model,the slot gap model and the striped wind model,can explain the radiation characteristics of pulsars,but the location of the radiation region and the multi-band radiation mechanism are still not solved.Based on the outer gap model,this paper mainly does the following work:(1)The light curve of 117 Fermi gamma-ray pulses was statistically studied.In this paper,a numerical fitting method is constructed for the optical curve of pulsar,which can give the relative ratio of the peak number,peak phase interval and peak intensity of the multi-band optical curve of pulsar.The statistical results show that 65.81% of pulsars have a bimodal structure.For normal pulsars,the phase interval between the two peaks ranges from 0.1 to 0.6 periods,concentrating between 0.3 and 0.6.The relative intensity of the two peaks in most bimodal pulsars shows obvious evolution with the increase of gamma ray energy.(2)The theoretical light curve is calculated based on the energy average external gap model,and the distribution of model parameters is statistically studied.According to the expected light curves,the pulsar's outer gap model can produce a typical bimodal light curve in a large parameter distribution range.Moreover,different radiation thickness and inner boundary position will have obvious influence on the shape of theoretical light curve.When the inner boundary position is lower than the zero charge surface,we can observe photons from the north and south poles at the same time.The contribution of the North Pole radiation is mainly distributed in P1,while P2 is small.The position of the inner boundary will significantly change the peak intensity ratio of the bimodal pulsar.For gaps of different thickness,the influence on the contour of the theoretical light curve is mainly reflected in the width of the peak.(3)Taking 29 young bimodal pulsars as samples,the theoretical model was combined with multi-band observations to limit the parameter distribution of the theoretical model,and the local physical parameters of the possible emission locations were statistically studied.The results show that photons may contribute to the light curve from a certain height on the pulsar surface to the light column.For typical young bimodal pulsars,the ratio of peak intensity to photon energy may be due to the combined effect of the local curvature radius and the height of the radiation region.