Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsh31b2017c&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SH31B-2017
Astronomy and Astrophysics
Astrophysics
[7514] Solar Physics, Astrophysics, And Astronomy / Energetic Particles, [7519] Solar Physics, Astrophysics, And Astronomy / Flares
Scientific paper
Understanding the origin of the high-energy solar energetic particles (SEPs) is a challanging problem due to the limited information provided by ground-level enhancements (GLEs) and the large energy gap between GLEs and the low-energy in-situ SEPs. These challenges are addressed for the first time with observations from the The Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) instrument, successfully launched in 2006 and expected to remain operational until at least the beginning of 2012. PAMELA measures energetic particles in the same energy range as ground-based neutron monitors but also extends to lower energies covered by statistically precise in-situ observations. The near-polar orbit of PAMELA translates to low rigidity cutoffs and thus extends the sensitivity to low-energy particles as low as ~20 MeV. It thus bridges an important gap between low energy in-situ observations and ground-based Ground Level Enhancements (GLE) observations, making it possible to consider the relationship in origin of these two populations. Composition also plays a key role in determining SEP origin (low corona and chromosphere vs. the high corona and solar wind). PAMELA is sensitive for the first time to the composition of the high-energy component of SEPs, measuring the charge (up to Z=6) and atomic number of the detected particles, and identifying and measuring positrons and neutrons-an unprecedented array of data channels that we can bring to bear on the origin of high-energy SEPs. The presence of secondaries, such as neutrons and positrons, could indicate a low coronal origin of these particles. Velocity dispersion of different species and over a wide energy range can be used to determine energetic particle release times at the Sun. We present results for several recent solar flares, registering both proton and helium enhancements in PAMELA. Together with multi-wavelength imaging and in-situ observations of a variety of species, we discuss PAMELA results and possible interpretations for the origins of the high-energy component of SEPs.
Bravar Ulisse
Christian Eric R.
de Nolfo Georgia Adair
Ryan Michael J.
Stochaj Stephen
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