Study On The Rotation Of Polarization Angle In Gamma-Ray Burst Prompt Phase

Gamma-ray burst(GRB)is the most violent explosive phenomenon in the universe.Polarization is an important aspect in the study of GRBs.The evolution of polarization angle has been observed in GRB170101A and GRB170114A,but there is no theory to explain it at present.This paper mainly studies the rotation of polarization angle in the prompt emission phase of GRB.In Chapter 1,the author first introduces the observation history and main observation characteristics of GRBs,and then introduces some theoretical models of the prompt emission phase of GRBs,focusing on the parameterization of the magnetic reconnection model.Finally,the author introduces some polarization correlation studies of the prompt emission phase of GRBs.From Chapter 2 to Chapter 3,the author studied the polarization of the prompt emission phase of GRBs during his master’s degree.In Chapter 2,the author calculated the light curves and polarization curves of the prompt emission phase of GRBs using the magnetic reconnection model.It was found that the degree of polarization degree would appear a small bump in the process of decay with time,and it was also found that the polarization angle rotated during off-axis observation.In order to explain the reason why the polarization degree bulge and the polarization angle rotate with time(energy),the author first calculated the evolution of the peak energy with time,and found that the polarization degree bulge is caused by the dependence of the synchrotron radiation polarization on the energy spectrum index.The author then drew a schematic diagram of flux and polarization on the sky plane,and calculated the change of Stokes parameter withθ(θis the angle between the velocity of fluid element and the direction of line of sight under the observer system).The correspondingθof Stokes parameter peak is expressed inθ_p.It is found that the rotation of polarization angle with time(energy)in off-axis observation is caused by the change of (?)orθ_p value.(?)is the ratio of the flux fromθcircles between (?)and (?)is the bulk Lorentz factor).(?)andθ_p are both related to the observed radiation region shape on one equal arrival time surface.Therefore,the change of the observed radiation region shape will lead to the rotation of the polarization angle.Chapter 3 introduces the use of magnetic reconnection model to fit GRB170101A and GRB 170114A,it is found that this model can explain the sharp polarization angle rotation of GRB170101A,but cannot predict the two 90°rotation of polarization angle in GRB170114A.Finally,the author summarizes the research work of polarization in the prompt emission phase of GRBs.