  We address the problem of how particles that are accelerated by solar flares
can escape promptly into the heliosphere, on time scales of an hour or less.
Impulsive solar energetic particles (SEP) bursts are generally observed in
association with so-called eruptive flares consisting of a coronal mass
ejection (CME) and a flare. These highly prompt SEPs are believed to be
accelerated directly by the flare, rather than by the CME shock, although the
precise mechanism by which the particles are accelerated remains controversial.
Whatever their origin, within the magnetic geometry of the standard
eruptive-flare model, the accelerated particles should remain trapped in the
closed magnetic fields of the coronal flare loops and the ejected flux rope. In
this case the particles would reach the Earth only after a delay of many hours
to a few days, when the bulk ejecta arrive at Earth. We propose that the
external magnetic reconnection intrinsic to the breakout model for CME
initiation can naturally account for the prompt escape of flare-accelerated
energetic particles onto open interplanetary magnetic flux tubes. We present
detailed 2.5D MHD simulations of a breakout CME/flare event with a background
isothermal solar wind. Our calculations demonstrate that if the event occurs
sufficiently near a coronal-hole boundary, interchange reconnection between
open and closed field can occur, which allows particles from deep inside the
ejected flux rope to access solar wind field lines soon after eruption. We
compare these results with the standard observations of impulsive SEPs and
discuss the implications of the model for further observations and
calculations.
