Cosmic Ray Anisotropy and Interstellar Spectra: Astrophysics of the Outer Heliosphere

• Applicant: Privatdozent Dr. Horst Fichtner
• Subject Area: Astrophysics and Astronomy
• Term: from 2012 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 226390020

Various measurements with ground- and space-based detectors have revealed the astrophysical relevance of a correct understanding of heliospheric physics. Most important for the proposed project are those observations related to outer bundary of the heliosphere. First, the determination of the local interstellar spectra of cosmic rays is improved continuously with the Voyager spacecraft. Second, the Voyagers and, particularly, the IBEX mission have increased our quantitative knowledge about the local interstellar magnetic field, plasma, and neutral gas surrounding the heliosphere. Both have triggered a refined understanding of cosmic ray modulation.Third, the hypothesis that the observed cosmic ray anisotropy in the low-TeV range is partly caused by the heliospheric structure, has recently gained new support from measurements with several terrestrial large area particle detectors and telescopes, as well as from theoretical considerations regarding, for example, magnetic reconnection in the heliotail. In order to judge on the various suggestions for the correct physical description of the outer heliosphere and its astrophysical relevance, we will develop quantitative models accounting for the large-scale structure of the heliosphere and its interstellar vicinity, particularly including the so-called heliosheath and heliotail as well as the local interstellar magnetic field. Consequently, the main objectives of the present proposal are defined as follows: We will extend our previous modelling of the large-scale heliosphere embedded in the interstellar medium by self-consistently including magnetic fields - especially with respect to the highly elongated heliospheric tail - and we will study the corresponding cosmic ray flux by solving both the transport equation and the equation of motion for these particles. Thus, we can test whether the heliotail indeed affects the anisotropy of the cosmic ray flux in the low-TeV range. Furthermore, this model allows us to study the effect of outer heliospheric structures on the local interstellar cosmic ray spectra. For these applications we will introduce new, so-called logically rectangular grids into heliospheric modelling since the presently used ones have severe shortcomings. These new grids have the advantages of being locally adjustable to the problem's geometry, avoiding both coordinate singularities and strongly differing cell sizes. The project results will consist of a modelling of our direct astrophysical environment, that will allow, for the first time, a quantitative interpretation of potential heliospheric signatures in astrophysical observations.

• DFG Programme: Research Grants
• International Connection: Austria
• Participating Person: Professor Dr. Ralf Kissmann