Signature of collapsars as sources for high-energy neutrinos and $r$-process nuclei

If collapsars are sources for both high-energy (HE) neutrinos and $r$-process nuclei, then the profuse low-energy antineutrinos from the $\beta$ decay of the newly synthesized nuclei can annihilate the HE neutrinos. Considering HE neutrinos produced at internal shocks induced by intermittent mildly magnetized jets, we show that such annihilation suppresses the overall HE neutrino spectrum at $\gtrsim 300\mathrm{TeV}$ and produces a corresponding flavor composition of $(F_{{\nu }_e+{\overline{\nu }}_e}:F_{{\nu }_{\mu }+{\overline{\nu }}_{\mu }}:F_{{\nu }_{\tau }+{\overline{\nu }}_{\tau }}{)}_{\star }\approx (1:10:1)$ at source. We find that the emergent HE neutrino flux can well fit the diffuse flux observed at IceCube if contributions from all similar sources are taken into account. Our results highlight the unique role of HE neutrinos in supporting collapsars as sources for $r$-process nuclei, and can be tested by detection of HE neutrinos from individual sources and accurate measurement of the diffuse HE neutrino flux spectrum and flavor composition.

Figure 1

Sketch of production of HE neutrinos (with energy $E_H$) and their annihilation with LE antineutrinos (with energy $E_L$) from $\beta$ decay of $r$-process nuclei in a collapsar.

Figure 2

HE neutrino spectra including annihilation with LE antineutrinos (solid curves) or not (dashed curves). Vacuum oscillations of LE antineutrinos are assumed. The benchmark case with $L_{\mathrm{iso}}={10}^{53}\mathrm{erg}/\mathrm{s}$ is shown in the left (${\nu }_e+{\nu }_{\mu }+{\nu }_{\tau }$ and ${\overline{\nu }}_e+{\overline{\nu }}_{\mu }+{\overline{\nu }}_{\tau }$) and middle (${\nu }_{\alpha }+{\overline{\nu }}_{\alpha }$ with $\alpha =e$, $\mu$, $\tau$) panels. Cases of $L_{\mathrm{iso}}={10}^{50}–{10}^{53}\mathrm{erg}/\mathrm{s}$ are shown in the right panel (all flavors). The inset shows the ratios of all-flavor spectra without annihilation to those with annihilation.

Figure 3

All-flavor diffuse neutrino flux spectra from our collapsar model with and without annihilation compared to IceCube data [101]. Contributions from jets with $L_{\mathrm{iso},53}=1$ at redshift $z=1$ are assumed to dominate. Results for different values of $\dot{m}\equiv \dot{M}/(M_{\odot }/\mathrm{s})$, asymmetric winds confined to ${\theta }^{\prime }=[0°,45°]$ and $[30°,45°]$, and the NH oscillation scenario for LE antineutrinos are also shown.