FRB 121102 Bursts Show Complex Time–Frequency Structure

By Jason W. T. Hessels, L. Spitler, A. Seymour, J. Cordes, D. Michilli, R. Lynch, K. Gourdji, A. Archibald, Cees G. Bassa, G. Bower and 16 more. Astrophysical Journal, 2018

252 citations recorded by the source corpus.

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

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/9f242b62887bfb5bee9c2b966a3c68eebce0c745

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Citations in the corpus

Fast Radio Burst Morphology in the First CHIME/FRB Catalog (2021, methodology): “The exact appearance of the structures depends on the choice of metric for dispersion optimization, but aligning subbursts assuming that all frequencies in one component were emitted at the source at the same time leads to the least scatter in dispersion measure (DM; Hessels et al. 2019).”
A Nearby Repeating Fast Radio Burst in the Direction of M81 (2021, background): “The dynamic spectrum of FRB 20200120E reveals downward-drifting time-frequency substructures that are thus far exclusively observed in the dynamic spectra of repeating FRBs (CHIME/FRB Collaboration et al. 2019a, 2019c; Hessels et al. 2019; Day et al. 2020; Fonseca et al. 2020).”
Fast radio bursts as synchrotron maser emission from decelerating relativistic blast waves (2019, background): “As we discuss in §3.2, the temporally decreasing peak frequency is also consistent with the observed downward drifting frequency structure in the sub-pulses of FRB 121102 (Hessels et al. 2018) and 180814.”