State-of-the-Art Collapsar Jet Simulations Imply Undetectable Subphotospheric Neutrinos

TL;DR

This study uses advanced simulations to show that subphotospheric neutrino production in collapsar jets is highly suppressed, implying such neutrinos are undetectable with current observatories and challenging previous assumptions.

Contribution

It demonstrates that high photospheric loading and magnetic effects prevent internal shocks and neutrino production deep in collapsar jets, revising prior models.

Findings

Subphotospheric neutrino production is suppressed below the photosphere.

Neutrinos with energies up to 10^5 GeV are expected from certain sources.

Such neutrinos are unlikely to contribute to the diffuse flux detected by IceCube.

Abstract

Mounting evidence suggests that the launching of collapsar jets is magnetically driven. Recent general relativistic magneto-hydrodynamic simulations of collapsars reveal that the jet is continuously loaded with baryons, owing to strong mixing with the cocoon. This results in a high photosphere at $\gtrsim 10^{12}$ cm. Consequently, collisionless internal shocks below the photosphere are disfavored, and the neutrino production in the deepest jet regions is prevented, in contrast to what has been assumed in the literature. We find that subphotospheric neutrino production could only take place in the presence of collisionless sub-shocks or magnetic reconnection. Efficient particle acceleration is not possible in the cocoon, at the cocoon-counter cocoon shock interface, or at the shock driven by the cocoon in the event of a jet halted in an extended envelope. These subphotospheric neutrinos have energy $E_\nu \lesssim 10^5$ GeV for initial jet magnetizations $\sigma_0=15$-$2000$. More than one neutrino and antineutrino event is expected to be observed in Hyper-Kamiokande and IceCube DeepCore for sources located at $z \lesssim \mathcal{O}(0.1)$. Because of their energy, these neutrinos do not contribute to the diffuse flux detected by the IceCube Neutrino Observatory. Our findings have implications on neutrino searches ranging from gamma-ray bursts to luminous fast blue optical transients.