MeV neutrino flash from neutron star mergers via r-process nucleosynthesis.

Detection of kilonova AT2017gfo proves that binary neutron star mergers can be the dominant contributor to the production of heavy elements in our Universe. Neutrinos from the radioactive decay of heavy elements would be the most direct messengers of merger ejecta. Based on r -process nucleosynthesis calculations, we study the neutrinos emitted from the β-decay of r -process elements and find that about half of the β-decay energy is carried away by neutrinos. The neutrino energy generation rate remains approximately constant at the early stage (t ≲ 1 s) and then decays as a power-law function with an index of −1.3. This powers a short-lived fast neutrino burst with a peak luminosity of ∼1049 erg s−1 in the early stage. Observation of neutrinos from neutron star mergers will be an important step towards understanding the properties of extremely neutron-rich nuclei and r -process nucleosynthesis, since the dominant contribution to the early time neutrino production is from nuclides near the r -process path. The typical neutrino energy is ≲8 MeV, which is within the energy ranges of the water-Cherenkov neutrino detectors such as Super-Kamiokande and future Hyper-Kamiokande, but the extremely low neutrino flux and event rate in our local Universe challenge the detection of the neutrino flashes. [ABSTRACT FROM AUTHOR]