Bayesian parameter study of the Seyfert-starburst composite galaxies NGC 1068 and NGC 7469

Journal article, 2026

Context. Multimessenger observations of the Seyfert-starburst composite galaxies NGC 1068 and NGC 7469 indicate a characteristic feature in the radio band (the so-called millimeter bump) as well as indication of high-energy neutrinos by the active galactic nucleus (AGN) corona. Moreover, the starburst ring of these sources is bright in the radio, and hence a potential source of gamma-rays and neutrinos.
Aims. We aim to explain the nonthermal features of these two sources with our homogeneous steady-state Seyfert-starburst composite model, which we refined in this work. Hereby, we account for stochastic diffuse acceleration and energy losses within the corona and gamma gamma-pair attenuation of the escaping gamma-rays. Methods. Since the nonthermal features of these Seyfert sources make a minor contribution in the electromagnetic spectrum, we are left with just a few data points that can be attributed to the starburst ring or the AGN corona. Hence, a proper inclusion of the prior information on the physical parameters is needed and subsequently used in the context of a Markov chain Monte Carlo approach to avoid overfitting. Results. Based on this Bayesian parameter study, we show that the nonthermal features of NGC 1068 can be explained well. Still a more detailed treatment of the spatial inhomogeneities in the central region of the AGN could further improve the fit results. This manifests itself even more clearly in the case of NGC 7469, where the millimeter bump needs to emerge from a coronal size of R-c > 100 & Rscr;(s) (with the Schwarzschild radius & Rscr;(s)), whereas (tera-electronvolt-peta-electronvolt)-neutrino emission requires R-c < 10 & Rscr;(s). Conclusions. Similar to what has previously been shown in other wave bands, our analysis highlights that the spatial extension of the so-called AGN corona depends on the considered energy of the messenger. Hence, it seems that there is not a unique edge of the corona and substantial progress in the understanding of these phenomena is expected if future analysis is to account for these spatial inhomogeneities.