[Paper Review] How much can we learn from SN1987A events? Or: An analysis with a two-Component model for the antineutrino signal

Francesco Vissani, G. Pagliaroli|ArXiv.org|Jul 8, 2008

Astrophysics and Cosmic Phenomena10 references3 citations

TL;DR

This paper analyzes SN1987A antineutrino data using a two-component model that separates early accretion-phase and later cooling-phase emission, improving agreement with the delayed scenario of core-collapse supernovae. It finds that the two-component model better fits the observed event times, energies, and angular distributions than the conventional one-component cooling model, supporting the presence of an initial intense neutrino burst consistent with theoretical expectations.

ABSTRACT

We analyze the data of Kamiokande-II, IMB, Baksan using a parameterized description of the antineutrino emission, that includes an initial phase of intense luminosity. The luminosity curve, the average energy of $\barν_e$ and the astrophysical parameters of the model, derived by fitting the observed events (energies, times and angles) are in reasonable agreement with the generic expectations of the delayed scenario for the explosion.

Motivation & Objective

• To test whether SN1987A data support the delayed scenario of core-collapse supernovae, which predicts an initial burst of intense neutrino luminosity.
• To compare the fit of a one-component cooling model versus a two-component model (accretion + cooling) to observed antineutrino events.
• To assess the consistency of the data with generic expectations of the delayed scenario, particularly the presence of an early, intense phase of electron antineutrino emission.
• To evaluate the impact of neutrino oscillations and detector-specific effects (background, dead time, angular bias) on the interpretation of the data.

Proposed method

• The two-component model describes antineutrino emission as a superposition of an initial accretion phase (lasting ~0.5 s, with a time-dependent temperature and luminosity) and a subsequent cooling phase with exponentially decaying temperature.
• The accretion phase is modeled using a time-dependent temperature profile T_a(t) = T_i + (T_f - T_i)(t/τ_a)^m, with m = 1–2, and a Gaussian-like time profile j(t) = exp[−(t/τ_a)^2] to describe the drop in neutron number.
• The total antineutrino flux is computed as Φ_ν̄_e(t) = Φ_a(t) + (1−j(t))Φ_c(t−τ_a), combining accretion and cooling contributions with a time shift.
• A likelihood function is constructed using event times, energies, and angular distributions, incorporating detector-specific effects such as background, dead time, and angular bias.
• The analysis includes neutrino oscillations using the PREM Earth matter model, with separate treatment for normal and inverted mass hierarchies.
• The model is fitted to data from Kamiokande-II, IMB, and Baksan using a joint log-likelihood function, with parameters including R_c, T_c, τ_c for cooling and T_a, τ_a, m for accretion.

Experimental results

Research questions

• RQ1 Does the two-component model (accretion + cooling) provide a better fit to SN1987A antineutrino data than the conventional one-component cooling model?
• RQ2 Are the observed event times, energies, and angular distributions consistent with the generic expectations of the delayed scenario, particularly the early burst of antineutrino emission?
• RQ3 To what extent do detector-specific effects—such as background, dead time, and angular bias—affect the interpretation of the data?
• RQ4 Can the data constrain the initial temperature and duration of the accretion phase, and how do these compare to theoretical predictions?
• RQ5 How do neutrino oscillations, particularly in the context of Earth matter effects, influence the observed antineutrino flux and the model fit?

Key findings

• The two-component model provides a significantly better fit to the SN1987A data than the one-component cooling model, particularly in reproducing the time distribution of events.
• The best-fit parameters for the accretion phase suggest an initial temperature T_a ≈ 0.6 T_c and a duration τ_a ≈ 0.5 s, consistent with theoretical expectations of the delayed scenario.
• The angular distribution of events in IMB is well explained by inverse beta decay, with no need to invoke exotic reactions or directional bias, despite initial concerns.
• The goodness-of-fit for angular distributions is better than 5%, indicating that the model is statistically consistent with the data.
• The inclusion of oscillations, particularly in the normal mass hierarchy, improves the agreement with the data, though the results are robust across both hierarchies.
• The analysis shows that models with rotation that predict a lower accretion temperature than the best-fit value are disfavored by the SN1987A data.