Composition and Abundance of Anomalous and Galactic Cosmic Rays: Implications of ACE Observations

The origin of Cosmic Rays (CRs) is a fundamental and central challenge to astrophysics. ACE, with its collection of high resolution spectrometers, offers a unique opportunity to address questions related to the elemental, isotopic and ionic charge state composition of energetic nuclei from H to Zn (1 <= Z <= 30). In particular, the Solar Isotope Spectrometer (SIS) and the Cosmic Ray Isotope Spectrometer (CRIS) provide a combination of instrumentation that allows one to investigate basic questions of cosmic ray origin (both anomalous and galactic), CR transport and energization, and the composition of the interstellar medium. SIS and CRIS measure elemental and isotopic composition over an energy range that encompasses the full anomalous cosmic ray (ACR) spectrum as well as low-energy galactic cosmic rays (GCRs).

The work proposed has two goals, the second of which cannot be addressed without a thorough understanding of the first. These are to use ACE observations (specifically SIS and CRIS) (1) to study the modulation of anomalous and galactic CRs of all species by the solar wind, and (2) to investigate possible sites of anomalous and galactic CR acceleration. At the energies measured by SIS and CRIS, both ACRs and GCRs experience substantial solar modulation. Accordingly, before any meaningful study of possible sites of CR energization can be undertaken, the observed modulated spectra must be understood in terms of the source spectra. This proposal therefore offers a dual approach for using the SIS and CRIS observations to address questions of basic importance to CR physics. The modulation goals of this research program are

• to develop CR diffusion tensor models based on detailed heliospheric turbulence transport models and to incorporate these into existing modulation codes.
• to explore the transport and modulation of CRs using more realistic 2D and 3D models of the global heliosphere.

Two possible sites for the acceleration of CRs will be considered: the termination shock for the acceleration of ACRs and supernova shocks for the acceleration of GCRs. For ACRs accelerated at the termination shock, we shall

• use observed ACR and pickup ion abundances to test and refine injection models for ACRs.
• investigate the acceleration of multiple ACR species at an ACR mediated termination shock and relate the models to SIS and CRIS spectra, and
• consider the acceleration of multiply charged ACRs.

• model particle acceleration at a blast wave driven into a progenitor stellar wind for a variety of supernova classes. The composition of the wind will be incorporated consistently, as will the structure of the stellar wind complex and the blast wave propagation. This will provide the elemental composition of the GCR spectrum as a function of energy which can then be compared (after suitable modulation) to CRIS data.

• Principal Investigator: Gary P. Zank, Bartol Research Institute, The University of Delaware, Newark, DE 19716.
  • Tel: (302) 831-8700, FAX: (302) 831-1843. zank@bartol.udel.edu
• Co-Investigator: Jacobus A. le Roux, Bartol Research Institute, The University of Delaware, Newark, DE 19716.
  • Tel: (302) 831-8700, FAX: (302) 831-1843. leroux@bartol.udel.edu

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