High-energy cosmic rays from γ-ray bursts

Abstract

A model is proposed for the origin of cosmic rays (CRs) from ∼ 10 14 eV/nucleon to the highest energies ( > ∼ 10 20 eV). GRBs are assumed to inject CR protons and ions into the interstellar medium of star-forming galaxies-including the Milky Waywith a power-law spectrum extending to a maximum energy ∼ 10 20 eV. The CR spectrum near the knee is fit with CRs trapped in the Galactic halo that were accelerated and injected by an earlier Galactic GRB. These CRs diffuse in the disk and halo of the Galaxy due to gyroresonant pitch-angle scattering with MHD turbulence in the Galaxy's magnetic field. The preliminary (2001) KASCADE data through the knee of the CR spectrum are fit by a model with energy-dependent propagation of CR ions from a single Galactic GRB. Ultra-high energy CRs (UHECRs), with energies above the ankle energy at > ∼ 3 × 10 18 eV, are assumed to propagate rectilinearly with their spectrum modified by photo-pion, photo-pair, and expansion losses. We fit the measured UHECR spectrum assuming comoving luminosity densities of GRB sources consistent with possible star formation rate histories of the universe.For power-law CR proton injection spectra with injection number index p > ∼ 2 and low and high-energy cutoffs, normalization to the local time-and space-averaged GRB luminosity density implies that if this model is correct, the nonthermal content in GRB blast waves is hadronically dominated by a factor ≈ 60-200, limited in its upper value by energetic and spectral considerations. Calculations show that 100 TeV -100 PeV neutrinos could be detected several times per year from all GRBs with kilometer-scale neutrino detectors such as IceCube, for GRB blast-wave Doppler factors δ < ∼ 200. GLAST measurements of γ-ray components and cutoffs will constrain the product of the nonthermal baryon loading and radiative efficiency, limit the Doppler factor, and test this scenario.

Enhanced cosmological GRB rates and implications for cosmogenic neutrinos

“…[75]), they may be able to contribute to the flux of lower-energy cosmic rays (since they have a high local rate [61]) and alleviate the need for an extension of the Galactic component. A recent Galactic GRB has also been proposed as a potential source of lower-energy cosmic rays [76]. While the Milky Way is generally metal-rich (contrary to observations of typical GRB hosts), it possesses a gradient in its metallicity distribution which may have allowed for a lowluminosity burst in the past.…”

“…While the Milky Way is generally metal-rich (contrary to observations of typical GRB hosts), it possesses a gradient in its metallicity distribution which may have allowed for a lowluminosity burst in the past. Alternatively, one can consider an E ÿ2:2 injection spectrum (as might be expected from relativistic shocks), which may offer a better fit at lower energies [37,76]. This would require a larger f CR , which itself may explain GRBs with low radiative efficiencies [76].…”

“…Alternatively, one can consider an E ÿ2:2 injection spectrum (as might be expected from relativistic shocks), which may offer a better fit at lower energies [37,76]. This would require a larger f CR , which itself may explain GRBs with low radiative efficiencies [76].…”

Transition from galactic to extragalactic cosmic rays

“…Hypernovae are assumed to be the sources of GRBs. Such a model for GCR was considered in [64]. The explosion occurred 2 Â 10 5 year ago at distance about 500 pc from the Sun.…”

Extragalactic cosmic rays and their signatures

“…one per million years in our galaxy. Such a model was developed in [26]. More recently another galactic model [27] also with GRBs as the sources was studied, with protons and Iron nuclei as accelerated particles and assuming diffusion of Iron nuclei in the galactic magnetic fields.…”