Stars as Laboratories for Fundamental Physics - MPP Theory Group

What Have We Learned from SN 1987A 503
Fig. 13.1. Relative duration of neutrino cooling of a SN core as a function
of the axion-nucleon Yukawa coupling g a . In the free-streaming limit axions
are emitted from the entire volume of the protoneutron star, in the trapping
limit from the “axion sphere” at about unit optical depth. The solid line is
according to the numerical cooling calculations (case B) of Burrows, Turner,
and Brinkmann (1989) and Burrows, Ressell, and Turner (1990); the dotted
line is an arbitrary completion of the curve to guide the eye. The signal
duration is measured by the quantity ∆t 90% discussed in the text; an average
for the IMB and Kamiokande detectors was taken.
or ν τ ’s decay. The final states could include ν e ’s which are detectable
at IMB and Kamiokande so that one can obtain late-time events by
a suitable combination of mass and lifetime. For a 17 keV Majorana
neutrino a lifetime around 10 4 s would allow one to explain the signal
duration even with a short emission time scale at the source (Simpson
1991; see also Cline 1992). In the following it will be assumed that this
is not the explanation of the observed signal duration.
Another loophole is that some or all of the late-time events at Kamiokande,
which are separated from the main bunch by a 7 s gap, were
caused by effects other than core cooling. Recall that a similar problem
exists with the x-ray observations of old neutrons stars (Sect. 2.3) where
it is not always clear that one is observing blackbody surface emission
from thermal cooling rather than magnetospherically produced x-rays.
In the present case, one possibility is the fall-back of material onto
the core, i.e. late-time accretion which could cause significant neutrino
emission. However, on the basis of an analytic estimate Janka (1995b)
has argued that even with extreme assumptions this is not a likely
explanation of the late events.