Sensitivity of Super-Kamiokande with Gadolinium to Low Energy Anti-neutrinos from Pre-supernova Emission

TL;DR

This paper explores how the upgraded Super-Kamiokande with gadolinium can detect low-energy anti-neutrinos from pre-supernova stars, enabling early warnings of imminent supernovae within hours and up to 600 parsecs.

Contribution

It demonstrates the potential of SK-Gd to detect pre-supernova neutrinos hours before collapse, significantly enhancing early warning capabilities.

Findings

Over 200 events could be detected 12 hours before collapse for a star at 200 pc.

Detection could occur up to 10 hours before collapse at a false alarm rate of once per century.

Pre-supernova stars could be detected up to 600 pc away with SK-Gd.

Abstract

Supernova detection is a major objective of the Super-Kamiokande (SK) experiment. In the next stage of SK (SK-Gd), gadolinium (Gd) sulfate will be added to the detector, which will improve the ability of the detector to identify neutrons. A core-collapse supernova will be preceded by an increasing flux of neutrinos and anti-neutrinos, from thermal and weak nuclear processes in the star, over a timescale of hours; some of which may be detected at SK-Gd. This could provide an early warning of an imminent core-collapse supernova, hours earlier than the detection of the neutrinos from core collapse. Electron anti-neutrino detection will rely on inverse beta decay events below the usual analysis energy threshold of SK, so Gd loading is vital to reduce backgrounds while maximising detection efficiency. Assuming normal neutrino mass ordering, more than 200 events could be detected in the final 12 hours before core collapse for a 15-25 solar mass star at around 200 pc, which is representative of the nearest red supergiant to Earth, $\mathrm{\alpha}$Ori (Betelgeuse). At a statistical false alarm rate of 1 per century, detection could be up to 10 hours before core collapse, and a pre-supernova star could be detected by SK-Gd up to 600 pc away. A pre-supernova alert could be provided to the astrophysics community following gadolinium loading.