Identification of a Local Sample of Gamma-Ray Bursts Consistent with a Magnetar Giant Flare Origin. (arXiv:2101.05144v2 [astro-ph.HE] UPDATED)

Identification of a Local Sample of Gamma-Ray Bursts Consistent with a Magnetar Giant Flare Origin. (arXiv:2101.05144v2 [astro-ph.HE] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Burns_E/0/1/0/all/0/1">E. Burns</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Svinkin_D/0/1/0/all/0/1">D. Svinkin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hurley_K/0/1/0/all/0/1">K. Hurley</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wadiasingh_Z/0/1/0/all/0/1">Z. Wadiasingh</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Negro_M/0/1/0/all/0/1">M. Negro</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Younes_G/0/1/0/all/0/1">G. Younes</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hamburg_R/0/1/0/all/0/1">R. Hamburg</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ridnaia_A/0/1/0/all/0/1">A. Ridnaia</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cook_D/0/1/0/all/0/1">D. Cook</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cenko_S/0/1/0/all/0/1">S. B. Cenko</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Aloisi_R/0/1/0/all/0/1">R. Aloisi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ashton_G/0/1/0/all/0/1">G. Ashton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Baring_M/0/1/0/all/0/1">M. Baring</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Briggs_M/0/1/0/all/0/1">M. S. Briggs</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Christensen_N/0/1/0/all/0/1">N. Christensen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Frederiks_D/0/1/0/all/0/1">D. Frederiks</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Goldstein_A/0/1/0/all/0/1">A. Goldstein</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hui_C/0/1/0/all/0/1">C. M. Hui</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kaplan_D/0/1/0/all/0/1">D. L. Kaplan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kasliwal_M/0/1/0/all/0/1">M. M. Kasliwal</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kocevski_D/0/1/0/all/0/1">D. Kocevski</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Roberts_O/0/1/0/all/0/1">O. J. Roberts</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Savchenko_V/0/1/0/all/0/1">V. Savchenko</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tohuvavohu_A/0/1/0/all/0/1">A. Tohuvavohu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Veres_P/0/1/0/all/0/1">P. Veres</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wilson_Hodge_C/0/1/0/all/0/1">C. A. Wilson-Hodge</a>

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 $4times10^{44}$ erg of
$R_{MGF}=3.8_{-3.1}^{+4.0}times10^5$ Gpc$^{-3}$ 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.

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