FAST Observations of an Extremely Active Episode of FRB 20201124A. IV. Spin Period Search

Abstract We report the properties of more than 800 bursts detected from repeating fast radio burst (FRB) source FRB 20201124A with Five-hundred-meter Aperture Spherical Telescope during an extremely active episode on UTC 2021 September 25th-28th in a series four papers. In this fourth paper series, we present systematic search spin period and linear acceleration object both 996 individual pulse peaks dedispersed time series. No credible was found data set. rule out presence significant periodicity range between 1 ms 100 s duty cycle <0.49 ± 0.08 (when profile is defined by von-Mises function, not boxcar function) up to 300 m ?2 each one-hour observing sessions, 0.6 all 4 days. These searches contest theoretical scenarios involving ms–100 isolated magnetar/pulsar surface magnetic field <10 15 G small (such as polar-cap emission mode) or pulsar companion star black hole M ? P b > 10 hr. also perform fine structures identify 53 unrelated millisecond-timescale “periods” multi-components highest significance 3.9 ? . The recovered are neither consistent nor harmonically related. Thus they likely come period. caution against claiming below ?4 one-off FRBs. discuss implications our results possible connections microstructures.