Stars as Laboratories for Fundamental Physics - MPP Theory Group

What Have We Learned from SN 1987A 511
was actually due to background (quite possible) and whether event
No. 1 was due to the prompt ν e burst (possible but not necessary).
The last events were registered at 5.6 s after the first (IMB) and 12.4 s
(Kamiokande II). Recall also that the absolute timing between the two
detectors is uncertain to within a minute although it seems plausible
that in both cases the first event essentially marks the arrival of the
first neutrinos. Finally, recall that the signal at Kamiokande II exhibits
a peculiar 7.3 s time gap before the last three events; event No. 9 was
registered at 1.9 s after the first. Naturally, it is worrisome that the
large Kamiokande time scale rests on the last three events, i.e. in order
to take the Kamiokande pulse duration seriously one needs to appeal
to a rare statistical fluctuation.
The total number of events observed is not very sensitive to the
amount of axion cooling which has an impact mostly on the late-time
neutrino signal. Interestingly, in the trapping regime (large g a ) the
number of events at IMB actually increases because the axionic energy
transfer heats the neutrino sphere to higher temperatures. N IMB responds
sensitively to the neutrino spectrum because of the high threshold
at IMB. However, for this reason it is a bad indicator for the actual
neutrino flux because the high-energy tail of the spectrum is relatively
uncertain. For example, if it is described by a Fermi-Dirac function
with a degeneracy parameter η = 2−3 rather than η = 0 reduces N IMB
by about a factor of two (Fig. 11.11).
No numerical results are available in the intermediate regime between
free streaming and trapping where the axion mean free path is
of order the neutron star radius. In this range of coupling constants
the impact of axions on the star is maximized. Moreover, a substantial
modification of the initial collapse phase obtains.
As emphasized before, the most sensitive observable is the duration
of the neutrino signal at the detectors. Therefore, nominally a range
of coupling constants 1×10 −10 < ∼ g < a ∼ 3×10 −7 is excluded. Within this
range the observed neutrino signal likely would be shortened too much
to be compatible with the observations.
13.5.2 Impact of Multiple-Scattering Effects
The results presented in the previous section were based on a naive
perturbative calculation of the axion emission rate without taking the
modification of the spin-density structure function into account that
must occur at high density as outlined in Sect. 4.6.7. The density dependence
of the axion emission rate is encapsuled in the spin-fluctuation