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# Program information file
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PROGRAM_ID           2024B007
PROGRAM_TITLE        Is the interstellar cosmic-ray flux time variable?
PROGRAM_INV1         Nick Indriolo
PROGRAM_INV2         Mark Wolfire
PROGRAM_INV3         Arshia Jacob
PROGRAM_INV4         Paola Caselli
PROGRAM_INV5         Alexei Ivlev
PROGRAM_SCICAT       galactic/interstellar medium
PROGRAM_ABSTRACT_BEG
The standard picture of cosmic-ray propagation is that particles are accelerated in discrete regions such as supernova remnants, before diffusing outward and forming a uniform background sea throughout the Galaxy. In this scenario, the cosmic-ray flux and associated ionization rate of hydrogen are expected to be constant at any location far from acceleration sites. Recent observations of a diffuse molecular cloud indicate that the abundance of H3+, a molecule that traces the cosmic-ray flux, has dropped by a factor of 2 over a timescale of 20 years. This can be interpreted as due to a decrease in the cosmic-ray flux in an interstellar cloud, something never before observed, and not expected in the standard model of Galactic cosmic-ray propagation. To confirm the decreased H3+ column density with high confidence, we propose high S/N iSHELL observations of the sight line where this effect has tentatively been seen.
PROGRAM_ABSTRACT_END