A probe of the maximum energetics of fast radio bursts through a prolific repeating source

Abstract

Fast radio bursts (FRBs) are sufficiently energetic to be detectable from luminosity distances up to at least seven billion parsecs (redshift $z>1$). Probing the maximum energies and luminosities of FRBs constrains their emission mechanism and cosmological population. Here we investigate the maximum energetics of a highly active repeater, FRB 20220912A, using 1,500 h of observations. We detect $130$ high-energy bursts and find a break in the burst energy distribution, with a flattening of the power-law slope at higher energy -- consistent with the behaviour of another highly active repeater, FRB 20201124A. There is a roughly equal split of integrated burst energy between the low- and high-energy regimes. Furthermore, we model the rate of the highest-energy bursts and find a turnover at a characteristic spectral energy density of $E_{\hat{I}}^{\text{char}}½=2.09_{-1.04}^{+3.78}\times 10^{32}$ erg/Hz. This characteristic maximum energy agrees well with observations of apparently one-off FRBs, suggesting a common physical mechanism for their emission. The extreme burst energies push radiation and source models to their limit: at this burst rate a typical magnetar ($B=10^{15}$ G) would deplete the energy stored in its magnetosphere in $\sim$ 2150 h, assuming a radio efficiency $\hat{I}{\mu }_{\mathrm{radio}}=10^{-5}$. We find that the high-energy bursts ($E_{\hat{I}}½>3\times 10^{30}$ erg Hz${}^{-1}$) play an important role in exhausting the energy budget of the source.

accepted for publication in MNRAS, see https://doi.org/10.1093/mnras/staf1937