Speaker
Description
We have shown in [1] that at ultra-high-energy (UHE) the Galactic diffuse gamma-ray emission is very patchy, due to the short residence time of cosmic rays in the Galaxy and the scarcity of Galactic PeVatrons. However, such a patchiness remains hard to firmly attribute to the diffuse component of the Galactic emission due to the presence of a population of unresolved pulsars whose contribution remains poorly constrained. Moreover, the same population of unresolved pulsars is also suspected of being responsible for an increase (up to a factor $3$) of the diffuse flux measured by LHAASO, making the interpretation of gamma-ray observations very challenging. However, neutrino observations, which exclusively track interactions of hadronic cosmic rays, can provide reliable answers to these questions. In particular, using our code incorporating stochastic distributions of cosmic-ray sources [1], we constrain the hadronic contribution to the diffuse gamma-ray background of LHAASO based on a fit of the IceCube neutrino data in a self-consistent way. While the diffuse gamma-ray background has a leptonic contribution that may reach a few tens of percent at few tens of $\rm{TeV}$, above $\sim100\,\rm{TeV}$ we find that it is largely dominated by its hadronic component with a minimal leptonic contribution [2]. Moreover, we show how future $\sim10\,\rm{km}^3$ neutrino observatories can provide unequivocal proofs of the patchy morphology of the UHE diffuse gamma-ray background and help to constrain the number of Galactic hadronic PeVatrons, their number, and the propagation of cosmic-rays around them.
[1] S. Kaci, G. Giacinti, JCAP 01, 049 (2025).
[2] S. Kaci, G. Giacinti, In prep. (2025).