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Positron transport in the interstellar medium
KTH, School of Engineering Sciences (SCI), Physics.
2009 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 508, no 3, 1099-1116 p.Article in journal (Refereed) Published
Abstract [en]

Aims. We seek to understand the propagation mechanisms of positrons in the interstellar medium (ISM). This understanding is a key to determine whether the spatial distribution of the annihilation emission observed in our Galaxy reflects the spatial distribution of positron sources and, therefore, makes it possible to place constraints on the origin of positrons. Methods. We review the different processes that are likely to affect the transport of positrons in the ISM. These processes fall into three broad categories: scattering off magnetohydrodynamic waves, collisions with particles of the interstellar gas, and advection with large-scale fluid motions. We assess the efficiency of each process and describe its impact on the propagation of positrons. We also develop a model of positron propagation, based on Monte-Carlo simulations, which enable us to estimate the distances traveled by positrons in the different phases of the ISM. Results. We find that low-energy (less than or similar to 10 MeV) positrons generally have negligible interactions with magnetohydrodynamic waves, insofar as these waves are heavily damped. Positron propagation is mainly controlled by collisions with gas particles. Under these circumstances, positrons can travel very large distances (up to similar to 30 kpc/n(H,cm-3) for 1 MeV positrons) along magnetic field lines before annihilating.

Place, publisher, year, edition, pages
2009. Vol. 508, no 3, 1099-1116 p.
Keyword [en]
gamma rays: theory, diffusion, plasmas
National Category
Astronomy, Astrophysics and Cosmology
URN: urn:nbn:se:kth:diva-32484DOI: 10.1051/0004-6361/200809830ISI: 000273057300005ScopusID: 2-s2.0-72849149306OAI: diva2:410914
QC 20110415Available from: 2011-04-15 Created: 2011-04-15 Last updated: 2011-04-15Bibliographically approved

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