FRB 121102 Bursts Show Complex Time–Frequency Structure

摘要: FRB 121102 is the only known repeating fast radio burst source. Here we analyze a wide-frequency-range (1–8 GHz) sample of high signal-to-noise, coherently dedispersed bursts detected using Arecibo and Green Bank telescopes. These reveal complex time–frequency structures that include subbursts with finite bandwidths. The frequency-dependent structure complicates determination dispersion measure (DM); argue it appropriate to use DM metric maximizes frequency-averaged pulse structure, as opposed peak find = 560.57 ± 0.07 pc cm−3 at MJD 57,644. After correcting for dispersive delay, have characteristic frequencies typically drift lower later times in total envelope. In 1.1–1.7 GHz band, ~0.5–1 ms typical bandwidths ranging from 100 400 MHz, rate ~200 MHz ms−1 toward frequencies. At higher frequencies, subburst are larger, on average. While these features could be intrinsic emission mechanism, they also imparted by propagation effects medium local Comparison DMs previous values literature suggests an increase ΔDM ~ 1–3 4 yr; though, this stochastic variation secular trend. This implies changes or additional source delay. Overall, results consistent previously proposed scenarios which embedded dense nebula.