Cosmic rays from the nearby starburst galaxy NGC 253: the effect of a
  low luminosity active galactic nucleus
  NGC 253 is a nearby starburst galaxy in the Sculptor group located at a
distance of 3.5 Mpc that has been suggested by some authors as a potential site
for cosmic-ray acceleration up to ultra-high energies. Its nuclear region is
heavily obscured by gas and dust, which prevents establishing whether or not
the galaxy harbours a supermassive black hole coexisting with the starburst.
Some sources have been proposed in the literature as candidates for an active
nucleus. In this work, we aim at determining the implications that the presence
of a supermassive black hole at the nucleus of NGC 253 might have on cosmic ray
acceleration. With this aim, we model the accretion flow on to the putative
active nucleus, and we evaluate the feasibility of particle acceleration by the
black hole dynamo mechanism. As a by-product, we explore the potential
contribution from non-thermal particles in the accretion flow to the
high-energy emission of the galaxy. We found that in the three most plausible
nucleus candidates, the emission of the accretion flow would inhibit the black
hole dynamo mechanism. To rule out completely the influence that a putative
nucleus in NGC 253 might have in cosmic-ray acceleration, a better
clarification concerning the true nature of the nucleus is needed.
