  It is unclear if neutron star mergers can explain the observed r-process
abundances of metal-poor stars. Collapsars, defined here as rotating massive
stars whose collapse results in a rapidly accreting disk around a black hole
that can launch jets, are a promising alternative. We find that we can produce
a self-consistent model in which a population of collapsars with stochastic
europium yields synthesizes all of the r-process material in metal-poor ([Fe/H]
< -2.5) stars. Our model reproduces the observed scatter and evolution of
scatter of [Eu/Fe] abundances. We find that if collapsars are the dominant
r-process site for metal-poor stars, r-process synthesis may be linked to
supernovae that produce long gamma-ray bursts. Our results also allow for the
possibility that core-collapse supernovae beyond those that launch gamma-ray
bursts also produce r-process material (e.g., potentially a subset of Type
Ic-BL supernovae). Furthermore, we identify collapsar jet properties (isotropic
energy, engine luminosity, or engine time) which may trace r-process yield and
verify that the amount of r-process yield produced per collapsar in our model
(~0.07 Msun) is consistent with other independent estimates. In the future,
achieving 0.05 dex precision on distribution scatter or a reliable selection
function would further constrain our probe of r-process production. Our model
would also hold for another prompt r-process site with a power-law yield, and
work is needed to determine if, for example, fast-merging neutron stars can
also explain abundance scatter.
