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Relativistic proton production during the 2001 April 15 solar event


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Bombardieri, DJ, Michael, KJ, Duldig, ML and Humble, JE 2007 , 'Relativistic proton production during the 2001 April 15 solar event' , The Astrophysical Journal, vol. 665 , pp. 813-823 .

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Extreme solar processes at the Sun on 2001 April 15 accelerated protons to relativistic energies, resulting in a groundlevel
enhancement in cosmic rays observed at Earth. The GOES 10 spacecraft measured the proton flux directly, and
ground-based observatories measured the secondary responses to higher energy protons.We have modeled the groundlevel
response to this event using a technique that deduces the spectrum, arrival direction, and anisotropy of the highenergy
protons. To investigate the acceleration process(es), we have employed theoretical shock and stochastic
acceleration spectral forms in our fits to spacecraft and neutron-monitor data. In the case of stochastic acceleration, we use
two different spectral forms. The first (model A) incorporates an idealized preacceleration step through monoenergetic
injection. The second (model B) incorporates a more realistic injection function using preacceleration by DC electric
fields in a reconnecting neutral current sheet.We find that at the rise, peak, and decline phases of the event (14:20, 14:30,
and 14:45 UT, respectively), the spectrum between 120 MeVand 10 GeVis best fitted by a shock acceleration spectral
form. This implies that protons were accelerated to relativistic energies either by a coronal shock or at the bow shock
of the 2001 April 15 coronal mass ejection. In addition, reinvestigation of the 2000 July 14 solar event using the more
realistic injection function (model B) further supports our earlier findings thatMHDturbulence arising from magnetic
reconnection from a dissipating neutral current sheet was important in relativistic proton production for that event.

Item Type: Article
Authors/Creators:Bombardieri, DJ and Michael, KJ and Duldig, ML and Humble, JE
Keywords: Sun: coronal mass ejections (CMEs) — Sun: flares
Journal or Publication Title: The Astrophysical Journal
Publisher: Univ Chicago press
ISSN: 0004-637X
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