Ultrahigh-energy cosmic ray production by turbulence in gamma-ray burst jets and cosmogenic neutrinos

Abstract

We propose a novel model to produce ultra-high-energy cosmic-rays (UHECRs) in gamma-ray burst (GRB) jets. After the prompt gamma-ray emission, hydrodynamical turbulence is excited in the GRB jets at or before the afterglow phase. The mildly relativistic turbulence stochastically accelerates protons. The acceleration rate is much slower than the usual first-order shock acceleration rate, but in this case it can be energy-independent. The resultant UHECR spectrum is so hard that the bulk energy is concentrated in the highest energy range, resulting in a moderate requirement for the typical cosmic ray luminosity of ∼ 10 53.5 erg s −1 . In this model, the secondary gamma-ray and neutrino emissions initiated by photopion production are significantly suppressed. Although the UHECR spectrum at injection shows a curved feature, this does not conflict with the observed UHECR spectral shape. The cosmogenic neutrino spectrum in the 10 17 -10 18 eV range becomes distinctively hard in this model, which may be verified by future observations.

Cosmic Ray Production in Supernovae

“…Galactic magnetars may also contribute. In all cases, high power and relativistic outflows are required to produce the most extreme CR energies (e.g., Waxman 1995, Blasi et al 2000, Arons 2003, Lemoine 2013, Asano & Mészáros 2016.…”

Gamma-Ray Bursts and Fast Transients

“…One possibility is that the gamma-rays arise at lower radii, e.g. in the photosphere, while cosmic rays are only accelerated in shocks further out, where the efficiency for photo-hadronic interaction producing neutrinos is low (Asano and Mészáros 2016). For a discussion of the physics and gamma-ray emission from GRB photospheres, see Beloborodov and Mészáros, 2016, elsewhere in this volume. Following the recent announcement of the first detection of gravitational waves from the merger of stellar mass binary black holes by LIGO (Abbott et al 2016) results from non-photonic GW searches are now eagerly awaited.…”

Acceleration of ultrahigh-energy cosmic rays in the early afterglows of gamma-ray bursts

“…Recently, a stochastic acceleration (SA) model of UHECRs via turbulence in GRB jets has been proposed to avoid the problems mentioned above [1]. The SA can yield a hard UHECR spectrum with shallow index p ≲ 2 [2].…”

“…In the previous work [1], the authors considered the SA process with the test-particle treatment and assume non-evolving parameters such as the particle injection rate and the diffusion coefficient. In fact, acceleration of particles consumes the turbulence energy, representing as a damping process.…”