Probing Stellar Clusters from Gaia DR2 as Galactic PeVatrons: I -- Expected Gamma-ray and Neutrino Emission (2403.16650v2)

Abstract: Young & massive stellar clusters (SCs) are a potential source of galactic cosmic rays up to very high energies as a result of two possible acceleration scenarios. Collective stellar winds from massive member stars form a wind-blown bubble with a termination shock at which particle acceleration to PeV energies may occur. Furthermore, shock acceleration may occur at SNRs expanding inside the bubble. By applying a model of cosmic ray acceleration at both the wind termination shock and SNR shocks to the catalog of known SCs derived from Gaia DR2, we aim to identify the most promising targets to search for evidence of PeVatron activity. Predictions for the secondary fluxes of gamma-ray and neutrino emission are derived based on particle acceleration at the collective wind TS and the subsequent hadro-nuclear interactions with the surrounding medium. Predictions from our modelling under baseline and optimistic scenarios are compared to data, finding consistent results. We estimate the detection prospects for future gamma-ray and neutrino experiments. We find that degree-scale angular sizes of the wind-blown bubbles are typical, that may pose a challenge for experimental detection. A shortlist of the most promising candidates is identified, with an anticipated flux range. Of order 10 SCs may be detectable with future facilities, and 1-3 could be currently operating as PeVatrons. Among these, three gamma-ray detected SCs have data that our model can consistently describe. Several further as-yet-undetected SCs offer promising targets for future observations, although the flux range allowed by our model can be large (> factor 10). The large angular size of the wind-blown bubble may lead to low surface brightness emission, worsening the problem of source confusion. Nevertheless, we discuss how further work will help to constrain SCs as PeVatron candidates. (abridged)