Fermi-LAT observations, from 2008 to 2020, unveiled spectral, temporal and spatial features of gamma-rays emission from the disk and halo of the sun that theoretical models are unable to explain.…

This federal contract award was granted by the National Aeronautics and Space Administration (NASA) to the University of Arizona, doing business as the Arizona Board of Regents. The $754,501 grant will fund research to investigate the role of galactic cosmic ray transport in the magnetic turbulence and switchbacks of the solar wind, as observed by NASA's Fermi Gamma-ray Space Telescope and Parker Solar Probe missions. The research aims to better understand the physical processes in the space environment from the Sun to the heliopause. This effort involves collaboration between the University of Arizona and Ohio State University, leveraging their expertise in particle transport modeling, radiation mechanisms, and Fermi-LAT data analysis. The award is not designated as a set-aside contract. It is part of NASA's broader efforts to explore and characterize fundamental processes within the heliosphere and throughout the universe, as described in the 2013-2022 Heliophysics Decadal Survey.

Fermi-LAT observations, from 2008 to 2020, unveiled spectral, temporal and spatial features of gamma-rays emission from the disk and halo of the sun that theoretical models are unable to explain. Linden ET AL. PRL, 121, 131103, 2018 showed that the available model (seckel ET AL., APJ, 382, 652, 1991), based on multi-GEV to TEV galactic cosmic-RAY (GCR) protons bouncing back from the solar atmosphere and therein producing outgoing gamma-rays, underpredicts the ~10 GEV photon flux by a factor ~10. These observations indirectly probe magnetic fields and GCR transport in the inner heliosphere and the solar atmosphere. Parker solar probe (PSP) has already reached the closest distance to the sun than any other spacecraft ever before. PSP unexpectedly found that the solar wind (SW) outflow is locally reversed in s-shaped structures, called switchbacks (bale ET AL. Nature, 1, 2019), that had been found by the previous mission helios as close as ~0.3 AU to the sun but are now known to be much more common closer to the sun. Science goals this proposal will investigate the role of the transport of GEV-TEV gcrs in the magnetic turbulence and in switchbacks by bridging PSP with one of the most successful and productive NASA mission of the past decade (fermi). The magnetic turbulence of the SW at small heliocentric distances, probed by gcrs, will be constrained by leveraging on the steadily increasing PSP database. In particular, we will investigate the switchbacks as turbulent or laminar trapping structures for multi-GEV protons around the sun. Secondly, we will model the transport of gcrs close to the sun atmosphere in a regime of low pitch-angle scattering frequency. Thirdly, we will compare radio maps in quiet SW to infer transport properties of energetic electrons, between MEV and GEV. Methodology we aim at a coordinated observations/modelling effort focusing on two different distances from the sun: in-situ measurements of PSP particles (isois, sweap) and PSP magnetic field (fields), multi-GEV flux observations from fermi-LAT. We leverage on a long-established versatile expertise: the univ of arizona will provide expertise in theory of particle transport in magnetic turbulence (test-particle simulations in magnetostatic turbulence, solution to the focused transport equation) and radiation mechanisms (neutral pion decay from protons, radio-synchrotron or inverse compton for electrons), modelling of PSP data ohio state univ. Will provide expertise on radiation mechanisms and on fermi-LAT data analysis. Statement of relevance this project directly addresses the overarching goal, as described in b.1 of the roses 2020 solicitation, explore and characterize the physical processes in the space environment from the sun to the heliopause and throughout the universe . The project also goes beyond the goal of NASA missions by addressing the fourth high-level science goal from the 2013-2022 heliophysics decadal survey ``solar and space physics: a science for a technological society'': discover and characterize fundamental processes that occur both within the heliosphere and throughout the universe . Management plan this proposal assigns well-defined tasks to the team members, essential to the completion of the project: univ. Of arizona team includes PI f. Fraschetti, CO-is j. Giacalone and j. Kota, one post-doctoral researcher (yet unidentified, will be hired according to their interest/expertise). Ohio state univ. Team includes CO-is a. Peter, j. Beacom and one identified graduate student.