An Unusual Short Gamma-Ray Burst with Properties Intermediate Between SGRB and Magnetar Giant Flare Populations

A small but important fraction of short gamma-ray bursts (SGRBs) may originate from magnetar giant flares in nearby galaxies, but the extragalactic sample remains scarce. Here, we report on an intriguing event, GRB 241204A, which exhibits a precursor, short variability timescales, a weak spectral lag, delayed GeV emission, and a high peak energy. Joint localization using Fermi and Konus-Wind identifies three plausible nearby host-galaxy candidates spanning z = 0.05–0.097. At these candidate-host redshifts, the burst lies in an ambiguous region between magnetar giant flares and short gamma-ray bursts on the Amati E p,z – E iso plane. While its isotropic-equivalent energy is consistent with ordinary short gamma-ray bursts, its peak energy is among the highest for the SGRB population. If interpreted as a magnetar giant flare, its energy would be 3 orders of magnitude higher than any known event of its kind. We compare the physical implications of the short-gamma-ray-burst and magnetar-giant-flare interpretations.