Identification of a Local Sample of Gamma-Ray Bursts Consistent with a Magnetar Giant Flare Origin

Cosmological Gamma-Ray Bursts (GRBs) are known to arise from distinct progenitor channels: short GRBs mostly neutron star mergers and long a rare type of core-collapse supernova (CCSN) called collapsars. Highly magnetized stars magnetars also generate energetic, short-duration gamma-ray transients Magnetar Giant Flares (MGFs). Three have been observed the Milky Way its satellite galaxies they suspected contribute third class extragalactic GRBs. We report unambiguous identification population 4 local ($<$5 Mpc) GRBs, adding GRB 070222 previously discussed events. While identified solely based on alignment nearby star-forming galaxies, their rise time isotropic energy release independently inconsistent with larger at $>$99.9% confidence. These properties, host non-detection in gravitational waves all point an MGF origin. Despite small sample, inferred volumetric rates for events above $4\times10^{44}$ erg $R_{MGF}=3.8_{-3.1}^{+4.0}\times10^5$ Gpc$^{-3}$ yr$^{-1}$ place MGFs as dominant transient detected sources. As suggested, these imply that some produce multiple MGFs, providing source repeating The favor common CCSN key progenitors magnetars.