Probing the Maximum Energy of Fast Radio Bursts Using Thousands of Sources from the Second CHIME/FRB Catalog

Quantifying the maximum energy of fast radio bursts (FRBs) can provide stringent constraints on their emission mechanisms and progenitor models. However, the most energetic bursts are rare, requiring a large sample of FRBs to detect them. In this work, we use the largest available such sample, 2998 one-off FRBs from the Second CHIME/FRB Catalog, to obtain a lower limit on the maximum energy (E^max_iso) of FRBs, assuming isotropic energy distribution from FRB sources. In the absence of known redshifts (z) for most sources, we present a framework that uses the dispersion measures (DMs) and fluences of these FRBs, together with the probability distribution of z given DM, to derive the lower limit on E^max_iso. We generate simulated FRB samples assuming different parameter values for a log-normal DMhost distribution and a Schechter function form of the FRB energy function to estimate how many outliers—FRBs with large DM contributions from the host galaxy or intervening galaxy halos—could artificially inflate this limit. After accounting for outliers, the lower limit on E^max_iso from Catalog 2 FRBs ranges between 1.1 × 10⁴¹ and 1.9 × 10⁴² erg, with best estimate 1.5 × 10⁴² erg. This limit is consistent with estimates of the Schechter function cutoff energy (E^max_iso) derived from much smaller FRB samples. Moreover, inferred energies of hundreds of FRBs appear collectively limited around ∼1042 erg, suggesting a physical limit on the energy reservoir of FRB sources. The corresponding isotropic-equivalent FRB source energy is consistent with the total energy available in a magnetar’s external dipole magnetic field, supporting magnetars as FRB progenitors.