Volume 395 - 37th International Cosmic Ray Conference (ICRC2021) - GAD - Gamma Ray Direct
Detection of the third class of gamma-ray bursts: magnetar giant flares.
M. Negro* and E. Burns
Full text: pdf
Pre-published on: July 17, 2021
Published on: March 18, 2022
Abstract
Around 11.4 million years ago a young, highly magnetized neutron star, a magnetar, in the Sculptor galaxy released an enormous amount of energy in the form of a giant flare. On April 15th 2020 some of the emitted photons were detected by a number of gamma-ray telescopes around Earth and Mars. While the analysis of this event, GRB 200415A, was interesting in its own right, it resulted in broader implications for both magnetar and gamma-ray burst (GRB) science. The resulting population study of magnetar giant flares (MGFs), led to the unambiguous identification of a distinct population of 4 local ($<5$ Mpc) short GRBs. 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. The inferred volumetric rates for events above $4\times10^{44}$ erg of $R=3.8^{+4.0}_{-3.1}\times10^{5}Gpc^{-3}yr^{-1}$ place MGFs as the dominant gamma-ray transient that have been 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 core-collapse supernova as key progenitors of magnetars.
DOI: https://doi.org/10.22323/1.395.0630
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