http://arxiv.org/abs/1810.00098
The binary neutron star merger GW170817 detected by Advanced LIGO/Virgo was followed by a short gamma-ray burst (GRB) and thermal radiation (‘kilonova’) powered by the radioactive decay of heavy nuclei synthesized in the merger ejecta by the rapid neutron capture process (‘r-process’). The large inferred quantity of ejecta is best understood as originating in an outflow from the accretion disk surrounding the newly-formed black hole, the same engine that was likely responsible for the GRB jet. Similar accretion flows accompany the collapse of rotating massive stars (‘collapsars’), powering the class of long GRBs and their associated supernovae. Here we show that collapsar accretion disks also produce neutron-rich outflows that synthesize heavy r-process nuclei, despite the comparatively proton-rich composition of the infalling star. Though occurring less frequently than mergers, the much greater accreted mass in collapsars—and their correspondingly larger disk wind ejecta—implicate them as dominant contributors to the Galactic r-process. Collapsars provide the rare r-process source needed to promptly enrich a small fraction of ultra-faint dwarf galaxies early in the Universe which is also compatible with the Galactic chemical enrichment of europium relative to iron over longer timescales. We predict an excess in the late-time near-infrared emission from GRB supernovae, testable by future observations.
D. Siegel, J. Barnes and B. Metzger
Tue, 2 Oct 18
64/84
Comments: 50 pages, 13 figures, 1 table. Submitted 21st September 2018
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