INTRODUCTION
In the final stages of stellar evolution, the interior of the star becomes hot and pressurized, and a large number of neutrinos are produced by thermal processes.
Such neutrinos, called pre-supernova neutrinos, are known to be detectable with Super-K and KamLAND for nearby starts such as Antares and Betelgeuse.
KamLAND and Super-K have established pre-supernova monitors in 2015 and 2021 respectively, to provide early alarms prior to supernovae.
However, no active alarms have been triggered by both experiments due to concerns about false alarms. The combined alarm system is the solution.
It can significantly reduce false alarms and increase alarm sensitivity. The combined system plans to start distributing alarms using GCN.
We will also continue to publish (semi)-realtime siginificance to registered users and respond to low-level alarm requests.
KamLAND and Super-K agreed to run the combined alarm system. This web page provides system features and a registration form to access real-time data.
The system accepts observed numbers of pre-supernova neutrino candidates and expected numbers of background from Super-K and KamLAND as input, and provides the correspondent false alarm rate as the output.
False Alarm Rate
The quantity false alarm rate is introduced to resolve the "Look Else-where Effects" and the correlations between the previous measurement and the current measurement.
It is the frequency of false alarms happening assuming null hypothesis is true. Its unit is [number per century].
When Super-K observed m candidates and KamLAND observed n candidates, the correspondent false alarm rate is found in the following manner:
- 1. Generate toy Monte-Carlo samples using the expected numbers of background.
- 2. List possible combinations of observed candidates and sort them in the order of significance.
- 3. Calculate the frequency that the significance of toy Monte-Carlo becomes larger than the significance of the current observed combination (m,n).
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Validity of the Result
The result is delivered in a text file which contains three values in one line, separated by comma. The three values are a false alarm rate, a Unix timestamp and a status code, from left to right.
The Unix timestamp shows when the result is generated (UTC+0). The results are updated every 5 minutes. Please treat the result with much care if it is delayed for more than 5 minutes.
The status code shows the status of the system. It can take value 0, 1, 2, and 3. The status code will be "1" when the Super-Kamiokande detector and the KamLAND detector are both in normal operation. If KamLAND is not in normal operation due to calibration works, test runs, etc., while Super-Kamiokande is functioning normally, the status code is 2. Conversely, if Super-Kamiokande is off while KamLAND is functioning, the status code is 3. If both detectors are off, the status code becomes "0", and the false alarm rate becomes "N/A".
We list all of the cases below:
- a. When both Super-Kamiokande and KamLAND are functioning normally, the output will be: "[Combined false alarm rate], [Time], 1".
- b. If Super-Kamiokande is functioning normally, while KamLAND is not, the output will be: "[Super-K only false alarm rate], [Time], 2".
- c. If KamLAND is functioning normally, while Super-Kamiokande is not, the output will be: "[KamLAND only false alarm rate], [Time], 3".
- d. If both detectors are offline, the output will be: "N/A, [Time], 0".
Format of the Result
The result is delivered in a text file which contains only one line.
The line consists of three values, which are false alarm rate, timestamp and status code, from left to right.
The values are separated by comma.
Registration form
- [1] K. Asakura et al., 'KamLAND Sensitivity to Neutrinos from Pre-Supernova Stars', 2016 ApJ 818 91
- [2] L. N. Machado et al., 'Pre-supernova Alert System for Super-Kamiokande', 2022 ApJ 935 40
This work is supported by JSPS KAKENHI Grant Numbers 19H05803 and 19H05807.
