Studies On The Physical Origin And Activity Properties Of Fast Radio Bursts

Fast radio bursts（FRBs）are mysterious radio bursts with extremely short durations and extremely high brightness temperatures.Its physical origin is still unknow at present,and the FRB area is one of the frontier topics in astrophysics.In this work,we introduce the research status of FRBs and study the periodic activities of FRBs.FRBs are found to be located in the cosmological distance,with large burst energy and short duration.Due to its brightness temperature up to 10³⁵K,the radiation mechanism must be coherent.FRBs are found at frequencies between 100 MHz and 8 GHz.Only FRB 200428 was observed to be associated with a hard X-ray burst,while for other FRBs the multi-wavelength transients have not been found so far.FRB 200428 and its associated X-rays were confirmed to come from a magnetar in the Milky Way,SGR J1935+2154,suggesting that the central engines of at least a part of FRBs are magnetars.Two possible physical models were proposed for FRBs.One proposed that an FRB origin from high-energy radiation from particles in the magnetosphere of a neutron star,similar to the scenario of radio pulsars.The another suggested that an FRB is produced in relativistic shock waves far from the magnetosphere.The propagation effects of FRBs can be used to study the properties of the FRB environment,such as circumburst medium,interstellar and intergalactic medium.At present,most FRBs are non-repeater.Only about two dozen sources of repeating bursts were identified.A few FRBs are characterized by periodic activities,such as FRB 180916B and FRB 121102.Considering the dynamic evolution of magnetars,we obtained the evolution of free precession of magnetars as FRB sources,and the observation period of an FRB repeater is assumed to be equal to the period of free precession.The age of the source can be constrained by the observed FRB period.Based on the dynamic evolution of magnetostar rotation,and considering the effects of magnetic dipole radiation and gravitational wave radiation on the rotation and obliquity,we adopt a wide and reasonable range for initial parameters,such as initial rotation period,initial magnetic field and deformation parameter.We calculated the evolution of a series of physical quantities such as magnetar rotation,obiquity,magnetic field and precession period.By deducting the age of the FRB period,we found that the age of the magnetar that can produce FRB is limited to several hundreds to several thousands years.This discovery is consistent with the observation of the magnetar SGR J1935+2154 associated with FRB 200428.And we also predicted that FRB period will gradually increase.Our result showed that the ages of magnetars are young,which is consistent with the hypothesis that FRBs originate from young magnetars.On this scenario,we also discuss the probability of observation and the longest active time on observation.These studies are expected to be further tested in future FRB observations.