Ultra-High-Energy Cosmic Rays from a Magnetized Strange Star Central Engine for Gamma-Ray Bursts
msra(2008)
摘要
Ultra-high-energy cosmic rays (UHECRs) have been tried to be related to the
most varied and powerful sources known in the universe. Gamma-ray bursts (GRBs)
are natural candidates. Here, we argue that cosmic rays can be accelerated by
large amplitude electromagnetic waves (LAEMWs) when the MHD approximation of
the field in the wind generated by the GRB's magnetized central engine breaks
down. The central engine considered here is a strange star born with
differential rotation from the accretion induced conversion of a neutron star
into a strange star in a low-mass X-ray binary system. The LAEMWs generated
this way accelerate light ions to the highest energies $E =
q\eta\Delta\Phi_{max}$ with an efficiency $\eta \sim 10^{-1}$ that accounts for
all plausible energy losses. Alternatively, we also consider the possibility
that, once formed, the LAEMWs are unstable to creation of a relativistically
strong electromagnetic turbulence due to an overturn instability. Under this
assumption, a lower limit to the efficiency of acceleration is estimated to be
about $\eta \sim 10^{-2.5}$. Due to their age, low mass X-ray binary systems
can be located in regions of low interstellar medium density as, e.g., globular
clusters or even intergalactic medium in case of high proper motion systems,
and cosmic ray energy losses due to proton collisions with photons at the
decelerating region are avoided, thus opening the possibility for particles to
exploit the full voltage available, well beyond that currently observed.
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关键词
globular cluster,ultra high energy cosmic ray,cosmic ray,neutron star,interstellar medium,electromagnetic waves,gamma ray burst
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