Production of High Energy Neutrinos in the Coronae of Ultraluminous X-ray Sources

Abstract

We investigate the possibility of high-energy neutrino production in coronae associated with ultraluminous X-ray sources (ULXs) as super-Eddington accreting black holes. Adopting the disk-wind-fed corona model, we calculate stochastic proton acceleration and the resulting neutrino emission from the ULX corona. We first examine whether the corona can be regarded as a collisionless plasma, which is a prerequisite for efficient non-thermal particle acceleration. We find that the collisionless condition is satisfied only when the mass accretion rate is lower than ($\sim 5\dot{M}_{\rm Edd}$). In this regime, protons are accelerated up to energies of a few tens of TeV and produce neutrinos through both photomeson ($p\gamma$) and hadronuclear ($pp$) interactions. The importance of hadronuclear interactions increases with accretion rate owing to the enhanced coronal density, resulting in broad neutrino spectra shaped by both $p\gamma$ and $pp$ processes. We also derive a correlation between neutrino and X-ray luminosities, ($L_{\nu,{\rm tot}} \propto L_X^{2.4}$), and estimate the neutrino flux from nearby ULXs. We show that M82 X-1 is among the most promising targets and may be detectable at the 90\% confidence level by future neutrino observatories. These results suggest that super-Eddington accreting black holes constitute a previously unexplored class of high-energy neutrino sources.