The Hadronic Picture of the Radiogalaxy M87

TL;DR

This paper explores hadronic models to explain the gamma-ray emission of M87, analyzing multi-year data, and predicts neutrino signals, challenging leptonic explanations and providing insights into cosmic ray acceleration in radio galaxies.

Contribution

It introduces hadronic scenarios for M87's gamma-ray emission, fitting spectral data with pion decay models, and predicts neutrino fluxes for detection prospects with km$^{3}$ neutrino telescopes.

Findings

Hadronic models fit the TeV gamma-ray spectra better than leptonic models.

Predicted neutrino fluxes from M87 are within the detection capabilities of current neutrino telescopes.

Constraints on giant lobe features are derived from ultra-high-energy observations.

Abstract

Very high energy gamma-ray emission of Fanaroff-Riley I objects is not univocally explained by a single emission model. Leptonic models with one and multi-zone emission regions, occurring in the jet of these objects, are usually used to describe the broadband spectral energy distribution. A correlation between the X-ray and TeV emission is naturally expected within leptonic models whereas a lack of correlation between these two observables represents a challenge and favors the hadronic scenarios. This is the case of M87 as we show here by analyzing its TeV and X-ray emission recorded in the last decade. Furthermore, we point out that the spectra obtained by MAGIC, H.E.S.S. and VERITAS telescopes cannot be described with the same leptonic model introduced by the Fermi-LAT collaboration. We introduce hadronic scenarios to explain the TeV gamma-ray fluxes of this radiogalaxy as products of Fermi-accelarated protons interacting with seed photons in the jet or thermal particles in the giant lobes. By fitting this part of spectral energy distribution as pion decay products, we obtain the expected neutrino counterpart and the luminosity of accelerating protons in the jet and/or lobes. With the expected neutrino fluxes we investigate, through Monte Carlo simulations, the possibility to see the signal from M87 with a Km$^{3}$ neutrino telescope, and compare the results with what has been seen by IceCube experiment up to now. Finally we constrain the features of giant lobes through the observations performed at ultra high energies by TA experiment.