Application Of Accretion-jet Model In FRB 20121102A And FRB 20190520B

Fast radio bursts(FRB)are bursts of radio frequency in the order of milliseconds.Various models have been proposed to explain the physical origin and radiation mechanism of fast radio bursts,but the physical origin and radiation mechanism are not fully understood.Fast radio bursts are classified into repeating bursts and non-repeating bursts according to whether they are repeated or not.In 2017 and 2022,researchers discovered two interesting repeating fast radio bursts(FRB20121102A and FRB 20190520B).They share many of the same characteristics: 1.They originated extragalactic;2.Large Faraday rotation measure(RM)are observed,where the Faraday rotation of FRB20121102 A is RM~10 rad m and the Faraday rotation of FRB20190520 B is RM~10 rad m.Such large Faraday rotations indicate that these two FRB are in an extreme,dynamic magnetic ion environment,and Faraday rotations larger than RM~10 rad m have only been observed in the vicinity of massive black holes.3.The presence of a persistent radio source(PRS)was observed.Some researchers have speculated that the large Faraday rotation observed in FRB 20121102 A and FRB 20190520 B may be strongly related to the existence of persistent radio sources,but persistent radio sources have not been studied much.Because the characteristics of persistent radio sources are similar to those of low accretion rate,low luminosity active galactic nuclei.A common model used in low luminosity active galactic nuclei is the coupling model of advection dominated accretion flow and jet.Therefore,the above accretion-jet model is adopted in this work to study the persistent radio source.We explain the energy spectrum distribution of the persistent radio sources of FRB20121102 A and FRB 20190520 B.By fitting the energy spectrum,we can restrict various physical quantities of the accretion-jet model,such as magnetic field intensity,electron number,etc.We calculate the Faraday rotation measure from each radius of the accretion disk and each height of the jet,and the following conclusions are obtained:1.The radiation from the persistent radio source of FRB 20121102 A and FRB 20195020 B comes mainly from the contribution of synchrotron radiation from non-hot electrons in the jet.No matter how we adjust the parameters of the accretion disk,we cannot fit the energy spectrum distribution of the persistent radio source well.2.The distribution of each physical quantity was obtained by fitting the energy spectrum distribution.However,due to the uncertainty of the polarization source,Faraday rotation values were calculated from the accretion disk and jet respectively.The results show that the Faraday rotation values of FRB 20121102 A and FRB 20190520 B calculated from the accretion disk are in good agreement with the observed values.FRB20121102 A and FRB 20190520 B Faraday rotation measure calculated from jets are much larger than observed values.Thus,the Faraday rotation observed for FRB 20121102 A and FRB 20190520 B may be due to the contribution of the accretion disk in the persistent radio source.3.The electron number density of FRB 20121102 A and FRB20190520 B shows an approximately power-law distribution,namely,9)∝.and 9)∝ ..If the distribution of electron number density can be observed,it will further confirm our conjecture.