Observations of presupernova neutrinos relating to the nal evolution of massive stars

We investigate neutrino events from presupernova stars at the distance of 200 pc detected by current and future neutrino observatories. The spectrum evolution of neutrinos emitted from presupernova stars of 12, 15, and 20 M ⨀ after the O burning until the core collapse is evaluated. The expected events are several to more than ten for KamLAND and are hundreds for JUNO and Hyper-K. The time evolution of the events could reveal the evidence for the change of burning processes during the nal evolution of massive stars. We propose the detection of presupernova neutrinos by Gd-loaded Super-K and Hyper-K using the delayed γ -ray signals of Gd( n, γ ) reaction. Gd-loaded Super-K and Hyper-K have a possibility for the detection of hundreds and thousands neutrino events, respectively. We also estimate the time for supernova alarms using presupernova neutrinos. KamLAND, JUNO, and other neutrino detectors could send supernova alarms using presupernova neutrinos several hours to one day before a supernova explosion. Multiple observations of presupernova neutrinos will raise the reliability of the supernova alarm.