The Supernova Early Warning System
When a massive star collapses at the end of its life, most of its binding energy is emitted in the form of neutrinos. These neutrinos emerge promptly from the stellar envelope over a timescale of tens of seconds. If the star later explodes, the burst of supernova photons does not become visible until hours later. We therefore expect to observe the neutrino burst from a Galactic supernova before we can see the optical counterpart in the sky. Although a Galactic supernova is rare and expected only every few decades, the next event will provide a unique opportunity to study these violent astrophysical phenomena.
The observation of a neutrino burst can thus provide a warning for astronomers that the opportunity to get a rare glimpse at the collapse of a star, resulting in a supernova, may soon be presenting itself. In addition, there is a real chance that a Galactic supernova may be observable with the naked eye, making this alert interesting to hobby astronomers and the general public alike. Most large-scale neutrino detectors around the globe thus joined forces in the SNEWS network to provide a high-sensitivity alert to interested parties. In addition, gravitational wave detectors like LIGO and Virgo have sensitivity to asymmetrically-collapsing supernovae and can both benefit from and contribute to such an alert.
The early supernova alert project has a central computer which accepts neutrino burst candidate messages from neutrino detectors around the world and sends an alert to astronomers if it finds a coincidence within a few seconds.
Research of the SNEWS collaboration is ongoing in a number of areas. We are improving the capabilities to accurately model supernova neutrino signals and triangulate the direction of the exploding star, and establishing optimized follow-up strategies to maximize the observational and scientific return.
For more information, please refer to this white paper describing SNEWS2.0.
There are a growing number of detectors sensitive to neutrinos from a galactic supernova. They vary widely in size, detection strategy, and sensitivity. Water Cherenkov detectors are based on the instrumentation of a mass of water with photomultiplier tubes, these include Super-Kamiokande, IceCube and KM3NeT. KamLAND, SNO+, NOvA are based on detections with pure liquid scintillators. HALO utilizes lead-based neutrino detections. Lead-based neutrino detection is possible through charged current or neutral current interactions with lead nuclei. Liquid noble dark matter detectors, like XENONnT, LZ, and PandaX-4T, are one of the leading targets for dark matter direct detection efforts. As the average neutrino energy is ∼10 MeV, the dominant cross section in liquid nobles is from the CEνNS interaction, which allows for a flavor-insensitive detection.