Gamma-ray bursts from the first stars: neutrino signals: Neutrino signals

If the first (PopIII) stars were very massive, their final fate is to collapse into very massive black holes. Once a proto-black hole has formed into the stellar core, accretion continues through a disc. It is widely accepted, though not confirmed, that magnetic fields drive an energetic jet which produces a burst of TeV neutrinos by photon-meson interaction, and eventually breaks out of the stellar envelope appearing as a gamma-ray burst (GRB). Based on recent numerical simulations and neutrino emission models, we predict the expected neutrino diffuse flux from these PopIII GRBs and compare it with the capabilities of present and planned detectors as AMANDA and IceCube. If beamed into 1 per cent of the sky, we find that the rate of PopIII GRBs is ≤ 4 × 10⁶yr^-1. High-energy neutrinos from PopIII GRBs could dominate the overall flux in two energy bands, [10⁴-10⁵]GeV and [10⁵-10⁶]GeV, of neutrino telescopes. The enhanced sensitivities of forthcoming detectors in the high-energy band (AMANDA-II, IceCube) will provide a fundamental insight on the characteristic explosion energies of PopIII GRBs, and will constitute a unique probe of the initial mass function (IMF) of the first stars and of the redshift z_f marking the metallicity-driven transition from a top-heavy to a normal IMF. The current upper limit set by AMANDA-B10 implies that such a transition must have occurred not later than z_f = 9.8 for the most plausible jet energies. Based on such results, we speculate that PopIII GRBs, if not chocked, could be associated with a new class of events detected by BeppoSax, the fast X-ray transients (FXTs), which are bright X-ray sources, with peak energies in the 2-10 keV band and durations between 10 and 200 s.