Cosmic rays from the nearby starburst galaxy NGC 253: the effect of a low-luminosity active galactic nucleus

Abstract

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 highenergy 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.

The Origin of Matter at the Base of Relativistic Jets in Active Galactic Nuclei

“…Under favourable conditions, the pairs can continue generating cascades outside the gap and the multiplicity can rise 100 times [16]. When the density of photons supplied by the RIAF is high, the cascades are too efficient within the gap and the electrostatic potential is screened; under this conditions leptons cannot be accelerated anymore [55]. This is the case for our fiducial model.…”

Exploring the superwind mechanism for generating ultrahigh-energy cosmic rays using large-scale modeling of starbursts

“…Observational guidance in assessing this conundrum is, at this point, essential. Tidal disruption events caused by black holes [22], low-luminosity gammaray bursts [78], and black hole unipolar induction [6] have been identified as potential UHECR accelerators inside starburst galaxies. However, all of these possible UHECR origins fail to explain which is the inherently unique feature(s) of starburst galaxies to account for their correlation [79].…”

“…It was conjectured that charged particles can be accelerated by bouncing back and forth across this terminal shock up to extremely high energies [2,3]. However, criticisms on the choice of model parameters characterizing the speed of the shock and magnetic field strength were reported in [4][5][6][7].…”

High-Energy Particles and Radiation in Star-Forming Regions

“…The latter are consistent with the CR energies accelerated in YMSCs (Bykov 2014), which are expected to be numerous in the starburst galaxies. Gutiérrez et al (2020) discussed a possible role of a massive black hole with a relatively low accretion rate as UHECR accelerator in the nucleus of starburst galaxy NGC 253. The origin of UHECR is possibly associated with the relativistic shocks in the outflows of compact objects (see e.g.…”