Supernova neutrino halo and the suppression of self-induced flavor conversion

Neutrinos streaming from a supernova core occasionally scatter in the envelope, producing a small “neutrino halo” with a much broader angle distribution than the primary flux originating directly from the core. Cherry et al. have recently pointed out that, during the accretion phase, the halo actually dominates neutrino-neutrino refraction at distances exceeding some 100 km. However, the multiangle matter effect (which increases if the angle distribution is broader) still appears to suppress self-induced flavor conversion during the accretion phase.

Figure 1

Intensity for the ${\overline{\nu }}_e$ radiation field of our numerical model, normalized to the forward direction, measured at the radial distances 300, 1000, 3000, and 10 000 km (right to left).

Figure 2

The ${10}^4\mathrm{km}$ numerical case (solid line) overlaid with the analytic fit (dashed line) of Eq. (2). We also indicate the power-law behavior estimated from an analytic argument (Sec. 2d).

Figure 3

Energy spectrum of core and halo components. Histogram: Numerical results. Smooth lines: Thermal spectra as described in the text with the same $T$.

Figure 4

Average $⟨1-\cos \theta ⟩$ for our analytic angle distribution of Eq. (2), representing the 280 ms numerical model.

Figure 5

Same as Fig. 4, now showing the enhancement caused by the halo, i.e., the ratio $\mathrm{total}/\mathrm{core}$ contribution, where the core flux is attributed to the first term in Eq. (2).

Figure 6

Contours for the indicated $\kappa r$ values in the parameter space of radius $r$ and assumed electron density $n_e$. We use a simplified energy spectrum as described in the text. The core flux alone is responsible for $\kappa r\gg 1$ for $r\lesssim 700\mathrm{km}$ (blue shading), and the halo adds the red-shaded region at larger $r$. We also show the density profile of our 280 ms numerical model.

Figure 7

Geometric definitions for the analytic halo estimate.