The Theoretical Study Of Gamma-Ray Binary’s High Energy Emission

Gamma-ray binary is composed of a massive main sequence star(O star or Be star)and a compact object,and is a short phase of massive binary’s evolution.So far 9 gamma-ray binaries have been detected.The compact objects of two gamma-ray binaries are identified to be pulsars.We expect that the compact objects of other gamma-ray binaries are pulsars.The gamma-ray binaries show a non-thermal spectrum from radio to Te V energy band,and the non-thermal spectrum originates from the shock due to the interaction between the pulsar wind and stellar wind.It has been suggested that the synchrotron and inverse-Compton process of the pulsar wind particles accelerated at the shock produces X-ray and Te V emissions,respectively.Gammaray binary offer a unique laboratory to study the physics of the pulsar wind and shock,as well as the evolution of the massive binary system.One important unresolved question of the pulsar wind is an energy conversion from the magnetic energy to the particle energy of the pulsar wind.Recent studies have suggested that the magnetic reconnection is the possible process of the energy conversion,but the site of the magnetic reconnection are still under debate.For an isolated pulsar,for example,the pulsar wind emission appears in so called pulsar wind nebulae,and the pulsar wind emission before the termination shock is difficult to be detected.For the gamma-ray binary system,if the pulsar is the compact object,it is expected that the inverse Compton process between the pulsar and and dense soft-photon field from the companion star produces high-energy emission.We expect therefore the study of the gamma-ray binary in the high-energy bands can be used to constrain the region of the energy conversion.It has been observed that the emission from the gamma-ray binaries are modulating with the orbital phase,and the peaks of the flux level in X-ray and Te V bands are aligned each other,which has been explained by the shock emission model.For Ge V emission,on the other hand,the peak position is generally shifted from those of X-ray and Te V bands.This suggests that mechanism of the the Ge V emission is different from that of X-ray or Te V emission.In this thesis,therefore,we explore a possibility that Ge V emission from some gamma-ray binaries is originated from the inverse-Compton process of the un-shocked pulsar wind before the shock.LMC P3 is most luminous gamma-ray binary so far,and is the first one which is detected outside the Milky Way galaxy.And it is 4 times at least more luminous than LS 5039 in Ge V band.The companion of LMC P3 is an O type star without deccretion disc.And this is suitable for us to study the properties of pulsar wind.We research the Ge V emission of LMC P3,and fit its Ge V light and spectrum based on known system parameters.We find that the observed amplitude of the orbital modulation,and the position of the Ge V peak relative to those of the X-ray and Te V bands can be explained by the current model.To explain the observed flux level in Ge V bands,we suggest that the energy conversion from the magnetic energy to the kinetic energy happens around the light cylinder of the pulsar.Another important question of the gamma-ray binary how to differentiate between the micro-quasar model and the pulsar wind model.In this thesis,we propose to use X-ray polarization properties to discriminate between two models.We expect that for the pulsar model,the polarization angle evolve 360 degree along the orbital phase,which its for the micro-quasar model expect a small variation of the polarization angle along the orbital phase.With the pulsar model,therefore,we investigate the possible polarization properties and discuss feasibility of the future observation,e.g.IXPE(Imaging X-ray Polarimetry Explorer).We expect that the X-ray emission from the gamma-ray binary system is produced by the synchrotron radiation from the shock.Because of the theoretical uncertainty of the magnetic structure of the shocked region,we explore three kinds of axisymmetric magnetic field structures:(i)toroidal magnetic field,(ii)poloidal magnetic field,and(iii)tangled magnetic field,and discuss the polarization properties for these three cases.We apply our model to bright gamma-ray binary LS 5039 and make predictions for future observations.LS 5039 is a gamma-ray binary in the Milky Way galaxy,and its X-ray flux is relatively high and very stable in long times scale.With the expected sensitivity of the IXPE,linear polarization of LS 5039 can be detected by an observation within one orbital period(3.9 days)if the magnetic field of LS 5039 is dominated by the toroidal magnetic field.If the magnetic field is dominated by the poloidal/tangled field,significant detection is expected with an observation longer than 10 days.