http://arxiv.org/abs/2212.00929
Gamma rays are produced by cosmic ray (CR) protons interacting with the particles at solar
photosphere and by cosmic ray electrons and positrons (CRes) via inverse Compton scattering of
solar photons. The former come from the solar disk while the latter extend beyond the disk.
Evaluation of these emissions requires the flux and spectrum of CRs in the vicinity of the Sun,
while most observations provide flux and spectra near the Earth, at around 1 AU from the Sun. Past
estimates of the quiet Sun gamma-ray emission use phenomenological modulation procedures to estimate
spectra near the Sun (see review by Orlando and Strong 2021 and references therein). We show that CRe transport in the inner heliosphere requires a kinetic approach and use a novel approximation to determine the variation of CRe flux and spectrum from 1 AU to the Sun including effects of (1) the structure of
large scale magnetic field, (2) small scale turbulence in the solar wind from several in situ measurements, in particular, those by Parker Solar Probe that extend this information to 0.1 AU, and (3) most importantly, energy losses due to synchrotron and inverse Compton processes. We present results on the flux and spectrum variation of CRes from 1 AU to the Sun for several transport models. In forthcoming
papers we will use these results for a more accurate estimate of quiet Sun inverse Compton gamma-ray spectra,
and, for the first time, the spectrum of extreme ultraviolet to hard X-ray photons produced by
synchrotron emission. These can be compared with the quiet Sun gamma-ray observation by Fermi (see, e.g.~Fermi-LAT Collaboration, 2011) and X-ray upper limits set by RHESSI (Hannah et al., 2010).
V. Petrosian, E. Orlando and A. Strong
Mon, 5 Dec 22
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Comments: 25 pages, 11 figures, in press Astrophysical Journal