Editing SN 1987A (section)

==Neutrino emissions==
Approximately two to three hours before the visible light from SN 1987A reached Earth, a burst of [[neutrino]]s was observed at three [[neutrino detector|neutrino observatories]]. This was likely due to [[Supernova neutrinos|neutrino emission]] which occurs simultaneously with core collapse, but before visible light is emitted as the shock wave reaches the stellar surface.<ref>
{{Cite book
 |last1=Nomoto |first1=K.
 |last2=Shigeyama |first2=T.
 |chapter=Supernova 1987A: Constraints on the Theoretical Model
 |editor-last1=Kafatos |editor-first1=M.
 |editor-last2=Michalitsianos |editor-first2=A.
 |editor2-link=Andreas Gerasimos Michalitsianos
 |title=Supernova 1987a in the Large Magellanic Cloud
 |at=§ 3.2
 |publisher=[[Cambridge University Press]]
 |isbn=978-0-521-35575-9
 |date=June 9, 1988
}}</ref> At 7:35 [[Universal Time|UT]], 12 [[antineutrino]]s were detected by [[Kamiokande II]], 8 by [[Irvine-Michigan-Brookhaven (detector)|IMB]], and 5 by [[Baksan Neutrino Observatory|Baksan]] in a burst lasting less than 13 seconds. Approximately three hours earlier, the [[Mont Blanc]] [[Neutrino detector#Scintillators|liquid scintillator]] detected a five-neutrino burst, but this is generally believed to not be associated with SN 1987A.<ref name=Arnett/>

The Kamiokande II detection, which at 12 neutrinos had the largest sample population, showed the neutrinos arriving in two distinct pulses. The first pulse at 07:35:35 comprised 9 neutrinos over a period of 1.915 seconds. A second pulse of three neutrinos arrived during a 3.220-second interval from 9.219 to 12.439 seconds after the beginning of the first pulse.{{citation needed|date=February 2021}}

Although only 25 neutrinos were detected during the event, it was a significant increase from the previously observed background level. This was the first time neutrinos known to be emitted from a supernova had been observed directly, which marked the beginning of [[neutrino astronomy]]. The observations were consistent with theoretical supernova models in which 99% of the energy of the collapse is radiated away in the form of neutrinos.<ref>
{{cite journal
 |last=Scholberg |first=K.|author-link=Kate Scholberg
 |year=2012
 |title=Supernova Neutrino Detection
 |journal=[[Annual Review of Nuclear and Particle Science]]
 |volume=62 |pages=81–103
 |arxiv=1205.6003
 |bibcode=2012ARNPS..62...81S
 |doi=10.1146/annurev-nucl-102711-095006 |doi-access=free
 |s2cid=3484486
}}</ref> The observations are also consistent with the models' estimates of a total neutrino count of 10<sup>58</sup> with a total energy of 10<sup>46</sup> joules, i.e. a mean value of some dozens of MeV per neutrino.<ref>
{{cite journal
 |last1=Pagliaroli |first1=G.
 |last2=Vissani |first2=F.
 |last3=Costantini |first3=M. L.
 |last4=Ianni |first4=A.
 |year=2009
 |title=Improved analysis of SN1987A antineutrino events
 |journal=[[Astroparticle Physics]]
 |volume=31 |issue=3 |page=163
 |arxiv=0810.0466
 |bibcode=2009APh....31..163P
 |doi=10.1016/j.astropartphys.2008.12.010
 |s2cid=119089069
}}</ref> Billions of neutrinos passed through a square centimeter on Earth.<ref>AAVSO 1987A</ref>

The neutrino measurements allowed upper bounds on neutrino mass and charge, as well as the number of flavors of neutrinos and other properties.<ref name=Arnett/> For example, the data show that the [[rest mass]] of the electron neutrino is <&nbsp;16&nbsp;eV/c<sup>2</sup> at 95% confidence, which is 30,000 times smaller than the [[mass of an electron]].  The data suggest that the total number of neutrino flavors is at most 8 but other observations and experiments give tighter estimates. Many of these results have since been confirmed or tightened by other neutrino experiments such as more careful analysis of solar neutrinos and atmospheric neutrinos as well as experiments with artificial neutrino sources.<ref>
{{cite journal
 |last1=Kato |first1=Chinami
 |last2=Nagakura |first2=Hiroki
 |last3=Furusawa |first3=Shun
 |last4=Takahashi |first4=Koh
 |last5=Umeda |first5=Hideyuki
 |last6=Yoshida |first6=Takashi
 |last7=Ishidoshiro |first7=Koji
 |last8=Yamada |first8=Shoichi
 |year=2017
 |title=Neutrino Emissions in All Flavors up to the Pre-bounce of Massive Stars and the Possibility of Their Detections
 |journal=[[The Astrophysical Journal]]
 |volume=848 |issue=1 |pages=48
 |arxiv=1704.05480
 |bibcode=2017ApJ...848...48K
 |doi=10.3847/1538-4357/aa8b72
 |s2cid=27696112
|doi-access=free
 }}</ref><ref>
{{cite journal
 |last1=Burrows |first1=Adam
 |last2=Klein |first2=D.
 |last3=Gandhi |first3=R.
 |year=1993
 |title=Supernova neutrino bursts, the SNO detector, and neutrino oscillations
 |journal=[[Nuclear Physics B: Proceedings Supplements]]
 |volume=31 |pages=408–412
 |bibcode=1993NuPhS..31..408B
 |doi=10.1016/0920-5632(93)90163-Z
}}</ref><ref>
{{cite journal
 |last1=Koshiba |first1=M.
 |year=1992
 |title=Observational neutrino astrophysics
 |journal=[[Physics Reports]]
 |volume=220 |issue=5–6 |pages=229–381
 |bibcode=1992PhR...220..229K
 |doi=10.1016/0370-1573(92)90083-C
}}</ref>