A bimodal burst energy distribution of a repeating fast radio burst source

A bimodal burst energy distribution of a repeating fast radio burst sourceWe have been carrying out a continuous monitoring campaign of FRB~121102 with the Five-hundred-meter Aperture Spherical radio Telescope (FAST\cite{li18}) since August 2019. Between August 29 and October 29, 2019, we detected 1652 independent burst events (see Supplementary Table 1) in a total of 59.5 hours, covering 1.05 GHz to 1.45 GHz with 98.304 $\mu$s sampling and 0.122 MHz frequency resolution. The total number of previously published bursts from this source was 347 (http://www.frbcat.org). The flux limit of this burst sample is at least three times lower than those of previous observations. The cadence and depth of the observations allow for a statistical study of the repeating bursts, revealing several previously unseen characteristics. The burst rate peaked at 122/hr on September 7th and then 117/hr on October 1st, both measured over the respective one-hour session. In both instances, the burst rate dropped precipitously afterwards. Burst energies vs. epoch are shown in the lower left and the energy histogram on the right, showing bimodality that is itself a function of epoch.Table format:Burst ID | Burst timea(MJD) | DM(pc cm-3) | Width(ms) | Bandwidthb(GHz) | Peak Flux(mJy) | Fluence(Jy ms) | Energy(erg)# Uncertainties in parentheses refer to the last quoted digit.a) Arrival time of burst peak at the solar system barycenter, after correcting to the frequency of 1.5GHz.b) A conservative 30$\%$ fractional error is assumed.