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

February 2021 • 2021ApJ...907L..28B

Authors • Burns, E. • Svinkin, D. • Hurley, K. • Wadiasingh, Z. • Negro, M. • Younes, G. • Hamburg, R. • Ridnaia, A. • Cook, D. • Cenko, S. B. • Aloisi, R. • Ashton, G. • Baring, M. • Briggs, M. S. • Christensen, N. • Frederiks, D. • Goldstein, A. • Hui, C. M. • Kaplan, D. L. • Kasliwal, M. M. • Kocevski, D. • Roberts, O. J. • Savchenko, V. • Tohuvavohu, A. • Veres, P. • Wilson-Hodge, C. A.

Abstract • Cosmological gamma-ray bursts (GRBs) are known to arise from distinct progenitor channels: short GRBs mostly from neutron star mergers and long GRBs from a rare type of core-collapse supernova (CCSN) called collapsars. Highly magnetized neutron stars called magnetars also generate energetic, short-duration gamma-ray transients called magnetar giant flares (MGFs). Three have been observed from the Milky Way and its satellite galaxies, and they have long been suspected to constitute a third class of extragalactic GRBs. We report the unambiguous identification of a distinct population of four local (<5 Mpc) short GRBs, adding GRB 070222 to previously discussed events. While identified solely based on alignment with nearby star-forming galaxies, their rise time and isotropic energy release are independently inconsistent with the larger short GRB population at >99.9% confidence. These properties, the host galaxies, and nondetection in gravitational waves all point to an extragalactic MGF origin. Despite the small sample, the inferred volumetric rates for events above 4 × 1044 erg of ${R}_{\mathrm{MGF}}={3.8}_{-3.1}^{+4.0}\times {10}^{5}$ Gpc-3 yr-1 make MGFs the dominant gamma-ray transient detected from extragalactic sources. As previously suggested, these rates imply that some magnetars produce multiple MGFs, providing a source of repeating GRBs. The rates and host galaxies favor common CCSN as key progenitors of magnetars.


IPAC Authors

David Cook

Assistant Scientist