Abstract
Gamma-ray bursts (GRBs) are short-lived, luminous explosions at cosmological distances, thought to originate from relativistic jets launched at the deaths of massive stars. They are among the prime candidates to produce the observed cosmic rays at the highest energies. Recent neutrino data have, however, started to constrain this possibility in the simplest models with only one emission zone. In the classical theory of GRBs, it is expected that particles are accelerated at mildly relativistic shocks generated by the collisions of material ejected from a central engine. Here we consider neutrino and cosmic-ray emission from multiple emission regions since these internal collisions must occur at very different radii, from below the photosphere all the way out to the circumburst medium, as a consequence of the efficient dissipation of kinetic energy. We demonstrate that the different messengers originate from different collision radii, which means that multi-messenger observations open windows for revealing the evolving GRB outflows.
Highlights
Gamma-ray bursts (GRBs) are short-lived, luminous explosions at cosmological distances, thought to originate from relativistic jets launched at the deaths of massive stars
The typical emission radius derived from prompt gamma rays cannot be directly applied to neutrino and ultra-high-energy cosmic rays (UHECRs) production, and the GRB will look very different
Nsh=100, Ncoll=87–97 teng=0.1 s, tv=0.53–0.66 s from the point of view of different messengers. This concept is well known from conventional astronomical observations, where astrophysical objects look very different in different wavelength bands
Summary
For the cosmic-ray and neutrino production, we follow refs 31,47 to compute the spectra for each collision individually, choosing equal energies in electrons (that is, photons) and magnetic field, and a baryonic loading of ten (that is, ten times more dissipated energy in protons than in photons). The more important reason is the significant baryonic loading: since most of the energy is dissipated into protons, the masses of the shells have to be upscaled to match the required energy output in gamma rays (1053 erg), which leads to larger radii of the photosphere because of higher electron densities. In the internal shock model, gamma-ray emission should be produced beyond the photosphere, so we only consider collisions beyond the photosphere in the following, unless noted otherwise This is conservative, since the baryonic loading may be smaller under the photosphere[10] and particle acceleration becomes inefficient for radiation-mediated shocks[50].
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