Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
K. Okamoto
K. Abe
Y. Hayato
K. Hiraide
K. Hosokawa
K. Ieki
M. Ikeda
J. Kameda
Y. Kanemura
Y. Kaneshima
Y. Kataoka
Y. Kashiwagi
S. Miki
S. Mine
M. Miura
S. Moriyama
Y. Nagao
M. Nakahata
Y. Nakano
S. Nakayama
Abstract： Neutrinos associated with solar flares (solar-flare neutrinos) provide information on particle acceleration mechanisms during the impulsive phase of solar flares. We searched using the Super-Kamiokande detector for neutrinos from solar flares that occurred during solar cycles $23$ and $24$, including the largest solar flare (X28.0) on November 4th, 2003. In order to minimize the background rate we searched for neutrino interactions within narrow time windows coincident with $\gamma$-rays and soft X-rays recorded by satellites. In addition, we performed the first attempt to search for solar-flare neutrinos from solar flares on the invisible side of the Sun by using the emission time of coronal mass ejections (CMEs). By selecting twenty powerful solar flares above X5.0 on the visible side and eight CMEs whose emission speed exceeds $2000$ $\mathrm{km \, s^{-1}}$ on the invisible side from 1996 to 2018, we found two (six) neutrino events coincident with solar flares occurring on the visible (invisible) side of the Sun, with a typical background rate of $0.10$ ($0.62$) events per flare in the MeV-GeV energy range. No significant solar-flare neutrino signal above the estimated background rate was observed. As a result we set the following upper limit on neutrino fluence at the Earth $\mathit{\Phi}<1.1\times10^{6}$ $\mathrm{cm^{-2}}$ at the $90\%$ confidence level for the largest solar flare. The resulting fluence limits allow us to constrain some of the theoretical models for solar-flare neutrino emission.
Peer Review Status:
Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
K. Abe
Y. Haga
Y. Hayato
K. Hiraide
K. Ieki
M. Ikeda
S. Imaizumi
K. Iyogi
J. Kameda
Y. Kanemura
Y. Kataoka
Y. Kato
Y. Kishimoto
S. Miki
S. Mine
M. Miura
T. Mochizuki
S. Moriyama
Y. Nagao
M. Nakahata
Abstract： We present the development of neutron-tagging techniques in Super-Kamiokande IV using a neural network analysis. The detection efficiency of neutron capture on hydrogen is estimated to be 26%, with a mis-tag rate of 0.016 per neutrino event. The uncertainty of the tagging efficiency is estimated to be 9.0%. Measurement of the tagging efficiency with data from an Americium-Beryllium calibration agrees with this value within 10%. The tagging procedure was performed on 3,244.4 days of SK-IV atmospheric neutrino data, identifying 18,091 neutrons in 26,473 neutrino events. The fitted neutron capture lifetime was measured as 218 \pm 9 \mu s.
Peer Review Status:Awaiting Review
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