Cosmic rays, neutrinos and GeV-TeV gamma rays from Starburst Galaxy NGC 4945

TL;DR

This paper investigates whether the starburst galaxy NGC 4945 could be the source of a high-energy neutrino event detected by IceCube, analyzing cosmic ray acceleration, gamma-ray emissions, and neutrino production.

Contribution

It provides a detailed analysis linking starburst galaxy properties to high-energy neutrino and gamma-ray observations, proposing NGC 4945 as a potential source of the IceCube event.

Findings

Interaction of protons with gas explains gamma-ray and radio observations.

Estimated neutrino event rate is too low for the central region to be the source.

Protons cannot be accelerated to ultra-high energies in the superwind region.

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 galaxy (SBG), 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 $\sim 10^{17} \, {\rm eV}$ 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 $\sim \rm mG$. Our estimated PeV neutrino events, in ten years, for this source is approximately 0.01 ($4\times10^{-4}$) 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 SBG. Additionally, we consider the superwind region of NGC 4945 and show that protons can hardly be accelerated in it up to UHEs.