Super-Kamiokande galactic supernova's
neutrino burst monitoring
Guillaume Pronost (ILANCE, CNRS - University of Tokyo),for the Super-Kamiokande collaboration
ICRC2023 Satellite Workshop Chiba U., August 7th 2023

Supported byMEXT KAKENHI
Grant Number
JP19H05807

Core-Collapse Supernova Neutrinos

SN1987A remnant▶ Since 1987A supernova (SN), we know that in case of supernova a burst of neutrino is

expected to be produced few minutes to several hours before the stellar explosion.
▶ If the SN is close enough, we can detect this burst on Earth and give an early warningto astronomers looking for the light from the stellar explosion.
ICRC2023 Satellite Workshop Chiba U.

2/20

guillaume.pronost@cnrs.fr

Super-Kamiokande▶ World leading Water Cherenkov detector located in the Kamioka Mine (Japan)• 50 kton water• ~2m OD viewed by 8-inch
PMTsOD• 32kt photo-sensitive volumeID• 22.5kt fid. vol.
(2m from wall)• SK-I: April 1996~• SK-VII is running▶ The detector is filled with 50ktons of gadolinium-loaded water.
▶ Gadolinium was loaded at 0.01% in the water in Summer 2020, and the concentration

was further increased to 0.03% in May 2022. Calibration was completed and the detector
is running stably since then.
▶ Physics targets: Neutrino Oscillations (Solar Neutrino, Atmospheric Neutrinos, T2K

beam), Nucleon decay, Astrophysics (Supernova burst, Diffuse Supernova Neutrino
Background, etc.)
ICRC2023 Satellite Workshop Chiba U.

3/20

guillaume.pronost@cnrs.fr

Why Gadolinium?
▶ Gadolinium is the stable nucleus with the highest neutron capture cross-section onEarth. The gadolinium-neutron capture produced a gamma cascade with a total energyof ~8 MeV, allowing to detect and reconstruct the neutron capture.
▶ This is specially useful to tag Inverse Beta Decay interactions

Hydrogen-neutron capture:single 2.2 MeV gamma→ Large accidental background→ Vertex reconstruction difficult
ICRC2023 Satellite Workshop Chiba U.

Gadolinium-neutron capture:
Gamma cascade at ~8 MeV→ Lower background→ Vertex reconstruction possible
4/20

guillaume.pronost@cnrs.fr

Supernova Neutrinos in Water Cherenkov Detectors▶ The SN neutrino burst is composed of(roughly) similar amount of neutrino andantineutrino of each flavours. However, dueto cross-sections, the number of detected
neutrino interaction will be different.
▶ In case of Water Cherenkov detector, themain interactions expected are:▷ Inverse Beta Decay reaction (IBD)→ ~90% of the expected interactions▷ Electron Scattering interactions (ES)

→ ~5% of the expected interactions
Keep the neutrino direction information▷ 16O interactions (CC and NC)→ ~5% of the expected interactions

ICRC2023 Satellite Workshop Chiba U.

5/20

guillaume.pronost@cnrs.fr

Using Gd-n to separate IBD and ES▶ Water cherenkov detector can extract the direction of the SN from the ES interactions▷ Separating ES from IBD allows to improve the SN direction pointing accuracy ofthe detector▷ We can use the characteristic delayed coincidence between the IBD’s positronemission and delayed neutron capture to tag IBD events.
→ Gd enhance the detectability of the neutron capture.

SN burst events w/o IBD tagging(10kpc simulation)

ICRC2023 Satellite Workshop Chiba U.

SN burst events w/ 72% IBD events tagged/removed(10kpc simulation)(Expected with 0.1% Gd)

6/20

guillaume.pronost@cnrs.fr

Realtime event selection▶ In order to monitor event burst within theOnline selection> 7 MeVSuper-Kamiokande detector, we arereconstructing and selecting “SNinteraction like” events in realtime.
▶ Realtime selection efficiencies:▷ ~35.3% of the ES interactions▷ ~89.5% of the IBD’s positron interactions

1000 MC simulations▷ ~54.4% of the IBD’s neutron capture# Eventsinteractions (with 0.03% Gd)→ ~46% IBD interactions are tagged
as IBD▶ These realtime efficiencies are lower than

the full performance of Super-Kamiokandeas hard cuts are applied to remove any
potential noise. Offline (slower) analysis
reach better performances.

τ ~ 61 μsec

1000 MC simulations
ICRC2023 Satellite Workshop Chiba U.

7/20

guillaume.pronost@cnrs.fr

Realtime angular resolution I▶ In June 2023, we deployed a new fitter (Maximum Likelihood + HEALPix) toimprove the speed and the efficiency of our Supernova direction reconstruction.
▶ With 0.03% Gd, our last realtime direction pointing accuracy is 3.96±0.13° at 10 kpc(Nakazato model). This reconstruction alone is achieved in less than 10 seconds(with respect to 1.5~2 minutes before).

ICRC2023 Satellite Workshop Chiba U.

8/20

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Realtime angular resolution with other models
Nakazato (ML fitter: 4.01±0.13°)

Preliminary

Preliminary

Fischer (ML fitter: 6.07±0.19°)

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306060PreliminaryMori (ML fitter: 4.55±0.14°)

Tamborra (ML fitter: 5.09±0.16°)

Preliminary
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Performances with the previous Maximum Likelihood (ML) fitter.
New fitter (ML+ HEALPix) performances are equivalent with a much faster processing.
ICRC2023 Satellite Workshop Chiba U.

9/20

guillaume.pronost@cnrs.fr

Automated SN alarm: GCN▶ In case of a burst of events matching our criteria (isotropic distribution and more than

60 good events) Super-Kamiokande will send an alarm. Since December 13th 2021, thisalarm is automated:▷ If the number of IBD tagged events is > 10, an automated GCN notice will bedistributed.
▷ This GCN notice is currently send by mail, which induces some delay to distribute it.
▷ GCN itself is under-going an upgrade (“Kafka”) recently, with an unified schema, anda new distribution method which we are implementing. This upgrade will reduce thedelay for the GCN notice distribution to less than 1 second.
Test GCN notice example

Preliminary ; 50kpc LMC (NK, Normal Hierarchy)
0.03% Gd

Note: this structure will change with the unified schema
ICRC2023 Satellite Workshop Chiba U.

10/20

guillaume.pronost@cnrs.fr

Realtime supernova monitoring in Super-Kamiokanderaw
data

Triggered data
Softwaretrigger

Realtime
reconstruction
and selection

Processed data

Alarm flowchart

Search forevent clusters
SN direction fitter

Event cluster
found!

# of IBD-tagged events > 10~1 h
Meeting, experts decide
if the SN is real andmanually send
worldwide announcement:
Atel, IAU-CBAT

true

ICRC2023 Satellite Workshop Chiba U.

automatically

Uniform vertex
Non-Uniform vertex
Automated GCN Notice
distribution
distribution

Call and mailto SK experts

Check cluster size

~1.5 minutes at present(for 10kpc SN)
aimed to be improved
to < 1 minute.

Automated GCN
noticeOfflineprocesses>60# of IBD-taggedevents > 10Golden alarm
11/20<25Silent alarm>25Normal alarm
guillaume.pronost@cnrs.fr

Supernova alarm in Super-Kamiokande▶ In case of supernova, SK would detect a burst of events for SN happening up to >100kpc(depending on the models assumed), and send Goldenalarms (automated) and Normal alarms (non-automated)▷ LMC is covered by Golden alarm

NK1 (20M, z=0.02, 200ms)▷ SMC is covered by Normal alarm(~90% probability for Golden alarm)
LMC SMC
16O

ICRC2023 Satellite Workshop Chiba U.

12/20

IBES D(CC)guillaume.pronost@cnrs.fr

Co-operation with telescopes▶ If (when) Super-Kamiokande send a supernova alarm to the world,

we hope some telescopes will be able to look for it in order toobserve the first instants of the supernova burst.
▷ In order to increase the probability our alarm will be used, tomaximise the change to have combined neutrino-opticalobservations of SN in the Milky Way, we are made a MoU in June 2023 with theAll-Sky Automated Survey for SuperNovae Collaboration (ASAS-SN), a network of 24
telescopes located around the globe▷ ASAS-SN implemented an automated follow-up of our SK alarm this month▶ If any other telescope collaborations or consortia are interested in making a direct,

minimum latency connection with Super-Kamiokande’s supernova alarm, pleasecontact us!

ICRC2023 Satellite Workshop Chiba U.

13/20

guillaume.pronost@cnrs.fr

Offline Supernova search▶ In case of supernovae (and failed supernovae) farther away than the SMC, our online

monitoring system may missed them. We also perform offline supernova search in ourdata.
Predicted supernova detection probability and number of events

M. Mori et al 2022 ApJ 938 35▶ We did not find any evidence of distant SN bursts from data collected in SK-IV(2008~2018), allowing to define the following upper limits:→ < 0.29 yr-1 supernovae out to 100 kpc (300 kpc for failed supernovae)▶ Coincidence with SN2023ixf was also investigated, but no significant signal was observed(ATEL 16070, GCN circular 33916)
ICRC2023 Satellite Workshop Chiba U.

14/20

guillaume.pronost@cnrs.fr

Pre-supernovae neutrinos▶ Before the core-collapse, supernova progenitors starts burning their C, O, Ne, and Si layers.

This burning produce a neutrino flux which can reach a luminosity of ~1012L☉ (whereas the5photon luminosity is ~10 L☉) [Astropart.Phys. 21 (2004) 303-313)]

e- + e+ →νx +νx▶ During the Si-layer burning (~few days before the core-collapse), the average neutrinoenergy is above the IBD threshold (1.8 MeV), allowing a potential detection in SuperKamiokande and the release of a pre-supernova alarm.
▶ For Betelgeuse (α-Ori) we can send a warning 10~15 hours before the core-collapse (NMO).
▶ This pre-supernova warning alarm

can allow detectors to avoid/
postpone maintenance or downtime few hours beforea supernova.

α-OriPreliminary▶ A combined alarm between

Plain: NMO
Dashed: IMO

Super-Kamiokande andKamLAND is now available:
https://www.lowbg.org/presnalarm/
ICRC2023 Satellite Workshop Chiba U.

0.03% Gadolinium

15/20

guillaume.pronost@cnrs.fr

Summary▶ Super-Kamiokande is continuously monitoring the detector events to probe any burst

indicating a supernova.
▷ Thanks to the 0.03% Gd loading in the detector water, we are able to tag ~46% of

the Inverse Beta Decay events, providing both a clear SN signal with low BG
contamination, as well as a mean to increase the accuracy of the SN direction reco.
▷ Super-Kamiokande monitoring system can provide a direction with a resolution of

3.96±0.13° at 10 kpc (assuming Nakazato model, NMO)
▷ We are releasing automated alarm through GCN notice within 1.5 minutes

following the neutrino burst in the detector.
▶ Pre-supernova neutrino can be detected few hours before the core-collapse inSuper-Kamiokande within 500 pc, further improvement can be expected by
combining Super-Kamiokande and KamLAND alarms.
▶ An MoU has been signed between ASAS-SN and Super-Kamiokande in order tomaximise our change for neutrino-optical detection of the next galactic supernova. If
any other telescope collaborations are interested in making a direct connection with
SK’s SN alarm, please contact us!
ICRC2023 Satellite Workshop Chiba U.

16/20

guillaume.pronost@cnrs.fr

Backup

ICRC2023 Satellite Workshop Chiba U.

17/20

guillaume.pronost@cnrs.fr

SN direction fitter improvement investigations▶ HEALPix based fitter (Hierarchical Equal Area isoLatitude Pixelation of a sphere):▷ A sphere of the sky is made and divided in pixels of equal area
▷ The pixels are populated with the projection of each event’s reconstructed direction on

the sphere.
▷ The sphere is then smoothed with a gaussian function▷ The pixel with the maximum number of events is then selected as the SN direction

Nside = 32, Npix = 12,288

ICRC2023 Satellite Workshop Chiba U.

Gaussian Smoothed, σ = 0.15 rad.

18/20

guillaume.pronost@cnrs.fr

Realtime angular resolution with other models
Hudelpohl (ML fitter: 5.11±0.16°) Preliminary

Preliminary

Wilson (ML fitter: 2.51±0.08°)

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ICRC2023 Satellite Workshop Chiba U.

19/20

guillaume.pronost@cnrs.fr

Realtime angular resolution with other models

ICRC2023 Satellite Workshop Chiba U.

20/20

guillaume.pronost@cnrs.fr