Cosmic rays, neutrinos, and GeV-TeV gamma rays from starburst galaxy NGC 4945

Abstract

The detection of high-energy astrophysical neutrinos and ultra-high-energy cosmic rays (UHECRs) provides a new way to explore sources of cosmic rays. One of the highest energy neutrino events detected by IceCube, tagged as IC35, is close to the UHECR anisotropy region detected by Pierre Auger Observatory. The nearby starburst (SB) galaxy, NGC 4945, is close to this anisotropic region and inside the mean angular error of the IC35 event. Considering the hypernovae contribution located in the SB region of NGC 4945, which can accelerate protons up to $\ensuremath{\sim}{10}^{17}\text{ }\text{ }\mathrm{eV}$ and inject them into the interstellar medium, we investigate the origin of this event around this starburst galaxy. We show that the interaction of these protons with the SB region's gas density could explain Fermi-LAT gamma-ray and radio observations if the magnetic field's strength in the SB region is the order of $\ensuremath{\sim}\mathrm{mG}$. Our estimated PeV neutrino events, in ten years, for this source is approximately 0.01 ($4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$) if a proton spectral index of 2.4 (2.7) is considered, which would demonstrate that IC35 is not produced in the central region of this SB galaxy. Additionally, we consider the superwind region of NGC 4945 and show that protons can hardly be accelerated in it up to UHECRs.