FAST Observations of an Extremely Active Episode of FRB 20201124A: I. Burst Morphology

Abstract

We report the properties of more than 600 bursts including cluster-bursts detected from the repeating fast radio burst (FRB) source FRB 20201124A with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) during an extremely active episode on UTC September 25-28, 2021, in a series of four papers. The observations were carried out in the band of 1.0 - 1.5~GHz by using the center beam of the L-band 19-beam receiver. We monitored the source in sixteen 1-hour sessions and one 3-hour session spanning 23 days. All the bursts were detected during the first four days. In this first paper of the series, we perform a detailed morphological study of 624 bursts using the 2-dimensional frequency-time “waterfall'' plots, with a burst (or cluster- burst) defined as an emission episode during which the adjacent emission peaks have a separation shorter than 400. The duration of a burst is therefore always longer than 1 ms, with the longest up to more than 120 ms. The emission spectra of the sub-bursts are typically narrow within the observing band with a characteristic width of ~277 MHz. The center frequency distribution has a dominant peak at about 1091.9 MHz and a secondary weak peak around 1327.9 MHz. Most bursts show a frequency-downward-drifting pattern. Based on the drifting patterns, we classify the bursts into five main categories: downward drifting (263) bursts, upward drifting (3) bursts, complex (203), no drifting (35) bursts, and no evidence for drifting (121) bursts. Subtypes are introduced based on the emission frequency range in the band (low, middle, high and wide) as well as the number of components in one burst (1, 2, or multiple). We measured a varying scintillation bandwidth from about 0.5~MHz at 1.0~GHz to 1.4~MHz at 1.5~GHz with a spectral index of 3.0.

Repeating Fast Radio Bursts Reveal Memory from Minutes to an Hour

“…Here we analyze the waiting time distributions for repeating FRB 20121102 and FRB 20201124A observed by FAST (Li et al 2021;Xu et al 2022). Here we combine the data of FRB 20201124A detected by FAST from April to May (Xu et al 2022) and September in 2021 (Zhou et al 2022). The observations of FRB 20121102 detected by Arecibo in 2016 (Hewitt et al 2022) and 2018 (Jahns et al 2023) are not included, by considering the instrument effects between different telescopes.…”

Fast Radio Bursts Generated by Coherent Curvature Radiation from Compressed Bunches for FRB 20190520B

“…However, some of the phenomena observed in FRB 20190520B have also been documented in other FRBs (Pleunis et al 2021), implying possible shared characteristics among them. For instance, the downward frequency drifting has been noted in many repeating FRBs, including FRB 20121102A (Hessels et al 2019) and FRB 20201124A (Zhou et al 2022). Moreover, for some FRBs, the flux of a single burst exhibits nonmonotonic variation trends with fluctuations or bright spots (Day et al 2020), such as FRB 20180814A (CHIME/FRB Collaboration et al 2019) and FRB 20180916B (Marcote et al 2020).…”

Repeating fast radio bursts reveal memory from minutes to an hour

“…Here we analyze the waiting time distributions for repeating FRB 121102 and FRB 201124A observed by FAST (Li et al 2021;Xu et al 2022). In order to reduce the statistical error caused by insufficient data, we combine the data of FRB 20201124A detected by FAST from April to May and September in 2021 (Zhou et al 2022). The waiting times are logarithmically divided into several bins.…”

“…Fast radio bursts (FRBs) are bright millisecond-duration astronomical transients (Lorimer et al 2007;Xiao et al 2021;Zhang 2022;Petroff et al 2022). Some FRBs, such as FRB 20121102A (Spitler et al 2016) and FRB 20201124A (Lanman et al 2022), are known to repeat, but it remains unclear whether repeating FRBs are prevalent or uncommon sources.…”