Fast radio bursts(FRBs)are bright,millisecond-duration radio emissions originating from cosmological distances.In this study,we report multi-year polarization measurements of four repeating FRBs initially discovered b...Fast radio bursts(FRBs)are bright,millisecond-duration radio emissions originating from cosmological distances.In this study,we report multi-year polarization measurements of four repeating FRBs initially discovered by the Canadian Hydrogen Intensity Mapping Experiment(CHIME):FRBs 20190117A,20190208A,20190303A,and 20190417A.We observed the four repeating FRBs with the Five-hundred-meter Aperture Spherical Radio Telescope(FAST),detecting a total of 66 bursts.Two bursts from FRB 20190417A exhibit a circular polarization signal-to-noise ratio greater than 7,with the highest circular polarization fraction recorded at 35.7%.While the bursts from FRBs 20190208A and 20190303A are highly linearly polarized,those from FRBs 20190117A and 20190417A show depolarization due to multi-path propagation,with σ_(RM)=2.78±0.05and 5.19±0.09 rad m^(-2),respectively.The linear polarization distributions among five repeating FRBs—FRBs 20190208A,20190303A,20201124A,20220912A,and 20240114A—are nearly identical but show distinct differences from those of nonrepeating FRBs.FRBs 20190117A,20190303A,and 20190417A exhibit substantial rotation measure(RM)variations between bursts,joining other repeating FRBs in this behavior.Combining these findings with published results,64% of repeating FRBs show RM variations greater than 50 rad m^(-2),and 21% exhibit RM reversals.A significant proportion of repeating FRBs reside in a dynamic magneto-ionic environment.The structure function of RM variations shows a power-law index of γ~(0-0.8),corresponding to a shallow power spectrum α=-(γ+2)~-(2.0-2.8)of turbulence,if the RM variations are attributed to turbulence.This suggests that the variations are dominated by small-scale RM density fluctuations.We perform K-S tests to compare the RMs of repeating and non-repeating FRBs,which reveal a marginal dichotomy in the distribution of their RMs.We caution that the observed dichotomy may be due to the small sample size and selection biases.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.12588202,12203045,12233002,12403100,12103069,and 12403042)the Leading Innovation and Entrepreneurship Team of Zhejiang Province of China(Grant No.2023R01008)+3 种基金the Key R&D Program of Zhejiang(Grant No.2024SSYS0012)supported by the National Natural Science Foundation of China(Grant No.12473047)the National SKA Program of China(Grant No.2022SKA0130100)the support from the Xinjiang Tianchi Program。
文摘Fast radio bursts(FRBs)are bright,millisecond-duration radio emissions originating from cosmological distances.In this study,we report multi-year polarization measurements of four repeating FRBs initially discovered by the Canadian Hydrogen Intensity Mapping Experiment(CHIME):FRBs 20190117A,20190208A,20190303A,and 20190417A.We observed the four repeating FRBs with the Five-hundred-meter Aperture Spherical Radio Telescope(FAST),detecting a total of 66 bursts.Two bursts from FRB 20190417A exhibit a circular polarization signal-to-noise ratio greater than 7,with the highest circular polarization fraction recorded at 35.7%.While the bursts from FRBs 20190208A and 20190303A are highly linearly polarized,those from FRBs 20190117A and 20190417A show depolarization due to multi-path propagation,with σ_(RM)=2.78±0.05and 5.19±0.09 rad m^(-2),respectively.The linear polarization distributions among five repeating FRBs—FRBs 20190208A,20190303A,20201124A,20220912A,and 20240114A—are nearly identical but show distinct differences from those of nonrepeating FRBs.FRBs 20190117A,20190303A,and 20190417A exhibit substantial rotation measure(RM)variations between bursts,joining other repeating FRBs in this behavior.Combining these findings with published results,64% of repeating FRBs show RM variations greater than 50 rad m^(-2),and 21% exhibit RM reversals.A significant proportion of repeating FRBs reside in a dynamic magneto-ionic environment.The structure function of RM variations shows a power-law index of γ~(0-0.8),corresponding to a shallow power spectrum α=-(γ+2)~-(2.0-2.8)of turbulence,if the RM variations are attributed to turbulence.This suggests that the variations are dominated by small-scale RM density fluctuations.We perform K-S tests to compare the RMs of repeating and non-repeating FRBs,which reveal a marginal dichotomy in the distribution of their RMs.We caution that the observed dichotomy may be due to the small sample size and selection biases.
