Authors: Vahe Petrosian, Stanford University

Particle Acceleration and Transport at the Flare Site and CME-driven Shock and their Interconnections

Vahe’ Petrosian, Stanford University, Stanford CA, 94305

Electrons and ions are accelerated in the solar flare re-connection sites and in the associated CME shock environments. Based on the radiative signatures of flares, stochastic acceleration by turbulence is the most likely acceleration mechanism. Turbulence and magnetic field geometry also govern the transport of particles down to the photosphere and out into the solar wind. This has been the primary focus of Solar Physics community. SEPs observed in situ are accelerated by the CME-shocks and has been primarily investigated by heliophysics community, concentrating mainly on their transport. While the seed particles for the flare site acceleration are known to be the background plasma particles, there has been a long standing question about the seed (suprathermal) particles for production of SEPs.

In the past there has not been the extensive investigation of the interrelation between the two sites and processes. However, in recent years there has been growing activity in this area due to new theoretical developments and, more importantly, new observations. One important interconnection is the idea that flare accelerated particles, escaping the re-connection site along open field lines connected to the CMEs, could be the seeds for a second phase acceleration by the CME-shock. This view is supported by the dichotomy between impulsive SEPs, with large enhancement of 3He and heavier ions, and gradual ones with nearly photospheric abundances. The second is provided by observation of solar flare gamma-rays, up to nearly 10 GeV, by the Fermi-LAT, which are often associated with fast CMEs and sometimes last many hours, and in same cases originated by flares located behind the limb (BTL) of the Sun. While CMEs are associated with type II radio emission, produced by upstream electrons, the gamma-rays, most likely produced by accelerated protons and ions, can be produced only at the photosphere. This has led to the possible scenario where by CME accelerated particles escaping the downstream of of the CME-shock toward the Sun could be the source of the gamma-rays, especially for the BTL flares, showing the other side of the interconnection.

I will review the observations and briefly describe the models for both acceleration and transport. This is directly connected to the LWS Focus Program on “Origin and Consequences of Suprathermal Particles that Seed Solar Energetic Particles.”