Journal Article

Cosmic ray protons in the energy range 10<sup>16</sup>–10<sup>18.5</sup> eV: stochastic gyroresonant acceleration in hypernova shocks?

Yi-Zhong Fan

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 389, issue 3, pages 1306-1310
Published in print September 2008 | ISSN: 0035-8711
Published online September 2008 | e-ISSN: 1365-2966 | DOI:
Cosmic ray protons in the energy range 1016–1018.5 eV: stochastic gyroresonant acceleration in hypernova shocks?

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The hypernovae (HNe) associated with gamma-ray bursts (GRBs) may have a fairly steep energy–velocity distribution, i.e. E(≥β) ∝βq for q < 2 and β≥βo, where β is the velocity of the material and βo∼ 0.1 is the velocity of the slowest ejecta of the HN explosion, both in units of the speed of light (c). The cosmic ray protons above the second knee but below the ankle may be accelerated by the HN shocks in the velocity range of β∼βo–4βo. When β≤ 4βo, the radius of the shock front to the central engine is very large and the medium decelerating the HN outflow is very likely to be homogeneous. With this argument, we show that for q∼ 1.7, as inferred from the optical modelling of SN 2003lw, the stochastic gyroresonant acceleration model can account for the spectrum change of high-energy protons around the second knee. The self-magnetized shock acceleration model, however, yields too steep a spectrum which is inconsistent with the observation unless the medium surrounding the HN is a free wind holding up to a radius ∼1–10 kpc.

Keywords: acceleration of particles; supernovae: general; cosmic rays; supernova remnants; gamma-rays: bursts

Journal Article.  4014 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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