Stars as Laboratories for Fundamental Physics - MPP Theory Group

Radiative Particle Decays 465
range (E γ,1 , E γ,2 ) for which one finds by integration of Eq. (12.15)
F γ,1,2 = F ν
m ν
τ γ
d LMC
2T ν
{
(1 − α) e −ε + 2α [ε E 2 (ε) + E 3 (ε)] } ∣ ∣ ∣∣
ε 1
ε 2
,
(12.16)
where the expression in braces is meant to be taken as a difference
between the two limits for ε. For ε 1 = 0 and ε 2 = ∞ it is equal
to 1, independently of α, as it must because the angular distribution of
photon emission leaves the total number of decay photons unchanged.
12.4.2 SMM Observations
The gamma ray spectrometer (GRS) on the SMM satellite consists of
seven NaI detectors surrounded on the sides by a CsI annulus and at
the back by a CsI detector plate (Forrest et al. 1980). The three energy
bands shown in Tab. 12.1 have been analyzed for γ-ray emission from
SN 1987A (Chupp, Vestrand, and Reppin 1989; Oberauer et al. 1993).
At the detection time of the first neutrino event at IMB (7:35:41.37 UT)
the GRS was observing the Sun. A time interval of 223.232 s until it
went into calibration mode was used to search for a photon signal above
background in each energy band. The background was determined by
analyzing the rates measured during an interval of 151.6 s before the
first neutrino event. In Fig. 12.7 the recorded number of events per
2.048 s is shown in each band as a function of time. No excess counts
were found in any of them and the distributions of the rates are in good
agreement with a Gaussian shape.
Because the GRS was observing the Sun, γ-rays associated with
the neutrino burst would have hit the instrument almost exactly from
the side and so they had to traverse about 2.5 g cm 2 of spacecraft aluminum
before being recognized in one of the detectors. This effect
has been included to calculate the effective detector areas which allow
one to convert “counts” into a γ-ray fluence. In Tab. 12.1 the corresponding
3σ limits are shown for the time until 223.232 s after the first
neutrino arrival (Oberauer et al. 1993). In order to constrain low-mass
neutrinos, only a time interval of 10 s around the burst is of interest;
the corresponding limits are also given (Chupp, Vestrand, and Reppin
1989). The fluence limits (cm −2 ) can be expressed as limits on an
average differential fluence (cm −2 MeV −1 ) by dividing with the width
∆E γ of a given channel. For the 10 s column they are shown as dotted
histograms in Fig. 12.6 while for 223.2 s they are shown in Fig. 12.13.