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  • Presentation | SH13A: Across the Heliospheric Boundaries and Regions: In Situ Observations and Modeling as Tools for Probing the Outer Heliosphere I Oral
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  • SH13A-05: A new low-energy cosmic ray population in the very local interstellar medium (invited)
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Author(s):
Matthew Hill, Johns Hopkins University Applied Physics Laboratory (First Author, Presenting Author)
Romina Nikoukar, Johns Hopkins Applied Physics Laboratory
Grant Berland, Applied Physics Laboratory Johns Hopkins
Kostas Dialynas, Office for Space Research and Technology, Academy of Athens
Vladimir Florinski, University of Alabama
Lawrence Brown, Applied Physics Laboratory Johns Hopkins
Alan Cummings, CALTECH
Robert Decker, The Johns Hopkins University. Applied Physics Laboratory
Douglas Hamilton, University of Maryland College Park
Marc Kornbleuth, Boston University
Stamatios Krimigis, Academy of Athens
Scott Lasley, University of Maryland College Park
Merav Opher, Boston University
Pontus Brandt, Johns Hopkins Univ/APL
Joe Giacalone, University of Arizona
Matina Gkioulidou, Johns Hopkins University Applied Physics Laboratory
Peter Kollmann, The Applied Physics Laboratory, John Hopkins University
Jozsef Kota, University of Arizona
Ralph McNutt, Johns Hopkins University Applied Physics Laboratory
Parisa Mostafavi, Applied Physics Laboratory Johns Hopkins
John Richardson, MIT
Edmond Roelof, Johns Hopkins University Applied Physics Laboratory


Galactic cosmic rays (GCRs) are energetic, electrically-charged particles, such as protons, that pervade the galaxy, until now only observed above ~3 MeV because of the impact of penetrating radiation on available low-energy measurements. We have address this challenge, e.g., with new computer simulations of the instrument response, using detailed knowledge of the LECP design, enabling us to newly observe 0.04–1 MeV GCR ions with the Voyager 1 & 2 LECP instruments, in the very local interstellar medium. GCRs have been explained by appealing to acceleration at supernovae shocks, but this new GCR population has a distinct power-law, suprathermal “tail” spectrum, more consistent with acceleration out of a core interstellar plasma population. The angular behavior of the new population is much like the higher energy GCRs, so they do not seem to originate in the heliosphere, and thus are galactic. This new population (1) may resolve a decades-long puzzle from astrochemical studies of diffuse interstellar clouds regarding the level of ionization attributed to traditional GCRs, (2) might generate sufficient pressure to explain the puzzling inability to account for the observed narrowness of the heliosheath, and (3) could help explained the gap between the observed and expected 0.05-MeV energetic neutral atom intensities.



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