Kavli Affiliate: Lina Necib
| First 5 Authors: Isabel S. Sands, Isabel S. Sands, , ,
| Summary:
The Milky Way’s galactic center is a highly dynamical, crowded environment.
Gamma ray observations of this region, such as the excess of GeV scale gamma
rays observed by Fermi LAT, have been of tremendous interest to both the high
energy astrophysics and particle physics communities. However, nearly all past
studies of gamma ray emission make simplifying assumptions about cosmic ray
(CR) propagation that may not be valid in the galactic center. Recent numerical
breakthroughs now enable fully time dependent dynamical evolution of CRs in
magnetohydrodynamic simulations with resolved, multi phase small scale
structure in the interstellar medium (ISM), allowing self consistent
comparisons to the Milky Way cosmic ray spectrum. We model diffuse gamma ray
emission from cosmic ray interactions for a set of Feedback in Realistic
Environments (FIRE) simulations of Milky Way mass galaxies run with spectrally
resolved cosmic ray spectra for multiple species at MeV to TeV energies. We
find that the galactic center gamma ray spectrum can vary by order of magnitude
amounts in normalization, and by approx. 10 percent in spectral slope at high
energies, driven by both injection from highly variable star formation and
losses from variable structure in the turbulent ISM. Gamma ray emission from
inverse Compton scattering and relativistic nonthermal Bremsstrahlung is
particularly variable on Myr timescales. We argue that features of the observed
Milky Way gamma ray spectrum may arise from such transient phenomena in gamma
rays produced from CR interactions.
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