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A recent detection of spatially extended gamma-ray emission in the centralregion of the Andromeda galaxy (M31) has led to several possible explanationsbeing put forth, including dark matter annihilation and millisecond pulsars.Another possibility is that the emission in M31 can be accounted for with apurely astrophysical cosmic-ray (CR) scenario. This scenario would lead to arich multi-wavelength emission that can, in turn, be used to test it.Relativistic cosmic-ray electrons (CRe) in magnetic fields produce radioemission through synchrotron radiation, while X-rays and gamma rays areproduced through inverse Compton scattering. Additionally, collisions ofprimary cosmic-ray protons (CRp) in the interstellar medium produce charged andneutral pions that then decay into secondary CRe (detectable through radiativeprocesses) and gamma-rays. Here, we explore the viability of a CR origin formulti-wavelength emission in M31, taking into consideration three scenarios: aCR scenario dominated by primary CRe, one dominated by CRp and the resultingsecondary CRe and gamma rays from neutral pion decay, and a final case in whichboth of these components exist simultaneously. We find that the multi-componentmodel is the most promising, and is able to fit the multi-wavelength spectrumfor a variety of astrophysical parameters consistent with previous studies ofM31 and of cosmic-ray physics. However, the CR power injection implied by ourmodels exceeds the estimated CR power injection from typical astrophysicalcosmic-ray sources such as supernovae.

Exploring A Cosmic-Ray Origin of the Multi-wavelength Emission in M31