This study investigates the antineutrinos production by β-decay of
r-process nuclei in two astrophysical sites that are capable of producing
gamma-ray bursts (GRBs): binary neutron star mergers (BNSMs) and collapsars,
which are promising sites for heavy element nucleosynthesis. We employ a
simplified method to compute the β-decay νˉe​ energy spectrum and
consider two representative thermodynamic trajectories for r-process
simulations, each with four sets of Ye​ distribution. The time evolution of
the νˉe​ spectrum is derived for both the dynamical ejecta and the disk
wind for BNSMs and collapsar outflow, based on approximated mass outflow rates.
Our results show that the νˉe​ has an average energy of approximately 3
to 9~MeV, with a high energy tail of up to 20 MeV. The νˉe​ flux
evolution is primarily determined by the outflow duration, and can thus remain
large for O(10)~s and O(100)~s for BNSMs and
collapsars, respectively. For a single merger or collapsar at 40~Mpc, the
νˉe​ flux is O(10−100)~cm−2~s−1, indicating a
possible detection horizon up to 0.1−1~Mpc for Hyper-kamiokande. We also
estimate their contributions to the diffuse νˉe​ background. Our results
suggest that although the flux from BNSMs is roughly 4--5 orders of magnitude
lower than that from the regular core-collapse supernovae, those from
collapsars can possibly contribute a non-negligible fraction to the total
diffuse νˉe​ flux at energy ≲1~MeV, with a large uncertainty
depending on the unknown rate of collapsars capable of hosting the r-process.Comment: 13 pages, 7 figure