Supernova neutrinos

Neutrinos produced in a stellar collapse

The observations of SN1987A

Optical observation 24 February 1987. Neutrino observations at February 23 7:35 UTC:
The dashed lines are observations of IMB [ref] and the continuos lines are of Kamiokande. [ref] The horizontal axis is time in seconds and the vertical axis is energy in MeV.

NEW: Observations of IMB

Photos displaying the computer output of the events recorded by the IMB detector (23 February 1987):

33162

33164

33167

33168

33170

33173

33179

33184,

courtesy of Prof Jack van der Velde.

The viewer's eye has been placed at the origin of what is probably an (anti)neutrino interaction on a proton giving a positron and a neutron. The neutron goes undetected but a positron produces a cone of Cherenkiv light in the water which is detected by some of the 2048 photomultiplier tubes (PMT's) arrayed on the six walls of the detector. Each wall is divided into rectangular patches outlined by a given color (red, blue, yellow). The small dashes and crosses represent outputs of individual PMT's. The number of lines is proportional to the light that hit the PMT and the color repserents the time of the hits. The time-color scale (in nanoseconds) is shown on the left.

The cones of Cherenkov light don't produce exact circles of PMT hits due to scattering and showering of the positrons in water. The best circle is event 33167. Event 33170 shows a Cherenkov cone grazing the blue and orange walls and then hitting the red wall head-on about 60 ns later.

The eight events came within a time itnerval of about 5 seconds, whereas the normal rate of such low energy events originating on the interior of the detector was about one every week. Hence the odds against these events being a statistical fluke are truly astronomical.

Properties of the supernova

One can make the following estimations from the neutrino and photon observations of SN1987A

• energy emitted in antineutrinos (3-6) 10 ⁴⁵ J
• energy emitted in all neutrinos (2 ± 1) 10 ⁴⁶ J
• kinetic energy (1.4 ± 0.1) 10 ⁴⁴ J
• the duration of the neutrino pulse 13 seconds

Implications of the observations of SN1987A for neutrino propeties

Future supernovae

Direction and spectrum refer to the ability of the detector to estimate (even statistically) the direction and energy spectrum of the neutrino burst. Expected events counts the number of events for a galactic supernova, inside 10 kpc. This is only an order of magnitude estimate. The efficiency of the detector may vary during the planning, the construction and the run.

Other supernova pages in the web