arXiv subjects

A. V. Olinto

Publications and source records attributed to A. V. Olinto.

41 records · Page 3Linked to original sources

arXiv2000

Ultra-High Energy Cosmic Rays from Young Neutron Star Winds

The long-held notion that the highest-energy cosmic rays are of distant extragalactic origin is challenged by observations that events above $\sim 10^{20}$ eV do not exhibit the expected high-energy cutoff from photopion production off the cosmic microwave background. We suggest that these unexpected ultra-high-energy events are due to iron nuclei accelerated from young strongly magnetized neutron stars through relativistic MHD winds. We find that neutron stars whose initial spin periods are shorter than $\sim 4 (B_S/10^{13}{\rm G})^{1/2}$ ms, where $B_S$ is the surface magnetic field, can accelerate iron cosmic rays to greater than $\sim 10^{20}$ eV. These ions can pass through the remnant of the supernova explosion that produced the neutron star without suffering significant spallation reactions. For plausible models of the Galactic magnetic field, the trajectories of the iron ions curve sufficiently to be consistent with the observed arrival directions of the highest energy events.

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arXiv2000

The Mystery of Ultra-High Energy Cosmic Rays

The origin of cosmic rays with energies higher than 10$^{20}$ eV remains a mystery. Accelerating particles up to these energies is a challenge even for the most energetic astrophysical objects known. While the isotropy in arrival directions argues for an extra-galactic origin, the photon-pion production off the cosmic background radiation limits the sources of such particles to systems less than 50 Mpc away from us. The combination of large gyroradii, efficient energy losses, and isotropic arrival directions defies most of the proposed astrophysical accelerators as well as the more exotic alternatives. I briefly review theoretical models for the acceleration and propagation of ultra-high-energy cosmic-rays and discuss the potential for future observatories to resolve this cosmic mystery.

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arXiv2000

Ultra High Energy Cosmic Rays: The theoretical challenge

The origin of the highest-energy cosmic rays remains a mystery. The lack of a high energy cutoff in the cosmic ray spectrum together with an apparently isotropic distribution of arrival directions have strongly constrained most models proposed for the generation of these particles. An overview of the present state of theoretical proposals is presented. Astrophysical accelerators as well as top-down scenarios are reviewed along with their most general signatures. The origin and nature of these ultra-high energy particles will be tested by future observations and may indicate as well as constrain physics beyond the standard model of particle physics.

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arXiv1999

Rapid dissipation of magnetic fields due to Hall current

We propose a mechanism for the fast dissipation of magnetic fields which is effective in a stratified medium where ion motions can be neglected. In such a medium, the field is frozen into the electrons and Hall currents prevail. Although Hall currents conserve magnetic energy, in the presence of density gradients, they are able to create current sheets which can be the sites for efficient dissipation of magnetic fields. We recover the frequency, $ω_{MH}$, for Hall oscillations modified by the presence of density gradients. We show that these oscillations can lead to the exchange of energy between different components of the field. We calculate the time evolution and show that magnetic fields can dissipate on a timescale of order $1/ω_{MH}$. This mechanism can play an important role for magnetic dissipation in systems with very steep density gradients where the ions are static such as those found in the solid crust of neutron stars.

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arXiv1999

Galactic Ultra-High-Energy Cosmic Rays

The absence of the expected GZK cutoff strongly challenges the notion that the highest-energy cosmic rays are of distant extragalactic origin. We discuss the possibility that these ultra-high-energy events originate in our Galaxy and propose that they may be due to iron nuclei accelerated from young, strongly magnetic neutron stars. Newly formed pulsars accelerate ions from their surface through relativistic MHD winds. We find that pulsars whose initial spin periods are shorter than $\sim 4 (B_S/10^{13}{\rm G})$ ms, where $B_S$ is the surface magnetic field, can accelerate iron ions to greater than $10^{20} eV$. These ions can pass through the remnant of the supernova explosion that produced the pulsar without suffering significant spallation reactions. Depending on the structure of the galactic magnetic field, the trajectories of the iron ions from galactic sources can be consistent with the observed arrival directions of the highest energy events.

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