Identification of a Local Sample of Gamma-Ray Bursts Consistent with a Magnetar Giant Flare Origin
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Date
2021-01-28
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Citation of Original Publication
Burns, E. et al. "Identification of a Local Sample of Gamma-Ray Bursts Consistent with a Magnetar Giant Flare Origin." The Astrophysical Journal Letters 907, no. 2 (28 January 2021). https://doi.org/10.3847/2041-8213/abd8c8
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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https://creativecommons.org/publicdomain/mark/1.0/
Public Domain
https://creativecommons.org/publicdomain/mark/1.0/
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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 contribute a third class of extragalactic GRBs. We report the unambiguous identification of a distinct population of 4 local (<5 Mpc) short GRBs, adding GRB 070222 to previously discussed events. While identified solely based on alignment to 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 non-detection 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 RMGF=3.8⁺⁴·⁰₋₃.₁×10⁵ Gpc⁻⁵ yr⁻¹ place MGFs as 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.