Study Of Counterparts Emission Of Fast Radio Bursts

Over ten years after the discovery of Fast Radio Bursts(FRBs),many ground-based radio telescopes have observed these events in the frequency range of 400 MHz-8 GHz,but they still remain mysterious from a physical point of view.They are charac-terized by very bright(?Jy)and very short(?ms)bursts of radio photons-The arrival time of a pulse at different frequencies is dispersed,and the delay time meets ?t ? v-2,which is consistent with the propagation of radio waves through cold plasma.Their large extra-galactic dispersion measures(DMsextragalactic?75-2600 pc cm-3)indicate their extragalactic or cosmological origins.This is supported by the identification of the host galaxy of FRB 121102:a dwarf galaxy with low metallicity and low star-forming rate at the redshift of z=0.193.The physical model of fast radio bursts needs to ex-plain how the high isotropic energy?1043 ergs-1 radiates in such a short timescale.This requires the introduction of coherent radiation process,and the radiation source should be very dense.In addition,FRBs have a variety of characteristics.At present,some of the observed FRBs have circular and/or linear polarization,and some of those have no polarization.Most of the pulse profiles have single peaks and a few have dou-ble or triple peaks.In addition,many FRBs show complex microstructure and features at timescales of tens of microseconds.FRBs are generally divided into non-repeating and repeating bursts.For a long time,FRB 121102 is the only observed repeating fast radio burst,accompanied by changing pulse shape and no obvious periodicity.Rotation Measure(RM)is much larger than other FRBs observed with RMs.After that,on August 14,2018,the Cana-dian Hydrogen Intensity Mapping Experiment(CHIME)telescope detected the second repeating fast radio burst,FRB 180814 J0422+73,which gains a lot of attention.For non-repeating FRB,many studies suggest that their non-repetitive characteristic is not yet determined,and their repeating bursts might have not yet been observed.There are many physical models of FRBs,such as a non-repeating FRB generated by magnetic braking when the neutron star binary merger,the repeating FRBs produced by magnetic reconnection when the two neutron stars interact,etc.Many models show that the physical origin of such astrophysical phenomenon are related to neutron stars.Quite a few studies have focused on the explosion model of this kind of repetitive FRBs and corresponding multi-wa'velength counterparts can help guide future observation strategies,speed up the process of eliminating theoretical models.Ultimately,we can unveil the mystery of fast radio bursts.This paper focus on the counterparts emission of FRBs,and study the specific characteristics of repeating FRBs and build a related physical model.This thesis is organized as follows:In Chapter 1,we give a brief overview of fast radio bursts.Firstly,the basic observation characteristics of FRBs are introduced,including dispersion measures,po-larization and rotation measures,pulse profiles and multi-wavelength counterparts.The physical models of fast radio bursts are briefly presented,and the relation with super-nova remnants(SNR)and gamma-ray bursts(GRB)are discussed in detail.In Chapter 2,we discuss the persistent radio counterpart of FRB 121102.Here we propose that this radio counterpart could arise from a pulsar wind nebula powered by a pulsar without surrounding supernova ejecta.Its medium is a stratified structure produced by a progenitor wind.The model parameters are constrained by the spectrum of the counterpart emission,the size of the nebula,and the large but decreasing rotation measure of the repeating bursts.In chapter 3,we focus on the second repetitive fast radio burst FRB 180814J0422+73.We use the ten-year Fermi Large Area Telescope(LAT)archival data to place flux and luminosity upper limits in the energy range of 100 MeV-10 GeV at the position of the source for an entire ten-year time span.We utilize these upper limits to constrain the fast radio burst progenitor and central engine.For the rotation-powered young magne-tar model,the external shock wave model and the off-axis GRB model,the upper limits can pose constraints on the allowed parameter space for the initial rotational period and surface magnetic field of the magnetar,the shock energy and the viewing angle,respectively.All of these constraints are more stringent if FRB 180814J0422+73 is at a closer distance.Finally,we summary our works and give a prospect of FRBs in the future in Chap-ter 4.