Spatial and Spectral Modeling of the Gamma-ray Distribution in the Large Magellanic Cloud

Abstract

We perform spatial and spectral analyses of the Large Magellanic Cloud (LMC) gamma-ray emission collected over 66 months by the Fermi Gamma-ray Space Telescope. In our spatial analysis, we model the LMC cosmic-ray distribution and gamma-ray production using observed maps of the LMC interstellar medium, star formation history, interstellar radiation field, and synchrotron emission. We use bootstrapping of the data to quantify the robustness of spatial model performance. We model the LMC gamma-ray spectrum using fitting functions derived from the physics of ${\pi }^0$ decay, bremsstrahlung, and inverse Compton scattering. We find the integrated gamma-ray flux of the LMC from 200 MeV to 20 GeV to be $1.38\pm 0.02\times 10^{-7}$ ph cm${}^{-2}$ s${}^{-1}$, of which we attribute about 10% to inverse Compton scattering and 40% to bremsstrahlung. From our work, we conclude that the spectral index of the LMC cosmic-ray proton population is 2.4$\pm$0.2, and we find that cosmic-ray energy loss through gamma-ray production is concentrated within a few hundred pc of acceleration sites. Assuming cosmic-ray energy equipartition with magnetic fields, we estimate LMC cosmic rays encounter an average magnetic field strength ~3 $\mu$G.

20 pages, 12 figures, published in ApJ

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• The EMU view of the Large Magellanic Cloud: Troubles for sub-TeV WIMPs
• Constraining cosmic ray acceleration in young star clusters using multi-wavelength observations
• Supernova origin of cosmic rays from a gamma-ray signal in the Constellation III region of the Large Magellanic Cloud
• Minimum Spanning Tree cluster analysis of the LMC region above 10 GeV: detection of the SNRs N 49B and N 63A
• Evidence of a spectral break in the gamma-ray emission of the disk component of Large Magellanic Cloud: a hadronic origin?
• Discovery of GeV gamma-ray emission from the LMC B0443-6657 with the Fermi Large Area Telescope
• Gamma-ray emission toward supergiant shells in the Large Magellanic Cloud