Probing cosmic-ray acceleration and propagation with H 3 + observations

Nick Indriolo, Brian D. Fields, Benjamin J. McCall

Research output: Chapter in Book/Report/Conference proceedingConference contribution


As cosmic rays traverse the interstellar medium (ISM) they interact with the ambient gas in various ways. These include ionization of atoms and molecules, spallation of nuclei, excitation of nuclear states, and production of pions among others. All of these interactions produce potential observables which may be used to trace the flux of cosmic rays. One such observable is the molecular ion H 3 + -produced via the ionization of an H 2 molecule and its subsequent collision with another H 2 -which can be identified by absorption lines in the 3.5-4 μm spectral region. We have detected H 3 + in several Galactic diffuse cloud sight lines and used the derived column densities to infer ζ 2 , the cosmic-ray ionization rate of H 2 . Ionization rates determined in this way vary from about 7×10 -17 s -1 to about 8×10 -16 s -1 , and suggest the possibility of discrete sources producing high local fluxes of low-energy cosmic rays. Theoretical calculations of the ionization rate from postulated cosmic-ray spectra also support this possibility. Our recent observations of H 3 + near the supernova remnant IC 443 (a likely site of cosmic-ray acceleration) point to even higher ionization rates, on the order of 10 -15 s -1 . Together, all of these results can further our understanding of the cosmic-ray spectrum both near the acceleration source and in the general Galactic ISM.

Original languageEnglish (US)
Title of host publicationProceedings of the International Conference of Computational Methods in Sciences and Engineering 2010, ICCMSE 2010
EditorsTheodore E. Simos, Theodore E. Simos, George Maroulis, Theodore E. Simos, Theodore E. Simos
PublisherAmerican Institute of Physics Inc.
Number of pages3
ISBN (Electronic)9780735412828
StatePublished - 2015
EventInternational Conference of Computational Methods in Sciences and Engineering 2010, ICCMSE 2010 - Psalidi, Kos, Greece
Duration: Oct 3 2010Oct 8 2010

Publication series

NameAIP Conference Proceedings
ISSN (Print)0094-243X
ISSN (Electronic)1551-7616


ConferenceInternational Conference of Computational Methods in Sciences and Engineering 2010, ICCMSE 2010
CityPsalidi, Kos


  • Cosmic Rays
  • Interstellar Medium
  • Supernova Remnants

ASJC Scopus subject areas

  • Physics and Astronomy(all)


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