A prolific repeating fast radio burst source and a crisis of the magnetar model

Magnetars are widely considered to be the central engine of fast radio bursts (FRBs), capable of driving coherent radio emission through magnetic energy release. The accumulation of burst energy can be employed as a probe to reveal the nature of FRB energy engine. Current observations of repeaters have not yet provided sufficient constraints on the magnetic energy budget for magnetar models. Here we report 11,553 bursts detected from the hyper-active repeating source FRB 20240114A over 214 days during a recent active episode, with a peak burst rate as high as 729 hr$^{-1}$, above the detection threshold of the monitoring observations using Five-hundred-meter Aperture Spherical radio Telescope (FAST). This represents the largest recorded burst sample from a single FRB source, comprising more than four times as many bursts as any previously known repeater and exceeding the cumulative total of all published bursts to date. Assuming a typical value of radio efficiency of $10^{-4}$ and a beaming factor of 0.1, the estimated total isotropic burst energy of this source exceeds 86\% of the dipolar magnetic energy of a typical magnetar with a polar surface magnetic field of $10^{15}$ G and a radius of $10^6$ cm. The total energy release of this source is about one and a half orders of magnitude higher than that of other known repeaters. We further provide the most stringent lower limit of $\bf{4.7\times10^{32}}$ G cm$^3$ on the magnetic moment of the underlying magnetar. The findings suggest that either the central engine emits with exceptionally high radio efficiency, possesses a small beaming factor, or it should be a more powerful compact object than typically considered in current magnetar models.