The expected potential of hadronic PeVatron searches with spectral γ-ray data from the Southern Wide-field Gamma-ray Observatory

Abstract

The presence of a spectral softening, occurring at $\sim$3 PeV energies, seen in the local cosmic-ray energy spectrum provides an evidence that our Galaxy hosts astrophysical objects, known as ’hadronic PeVatrons’, that are capable of accelerating hadrons to PeV energies and above. Recent results from ground-based particle detector array experiments have provided conclusive evidence that these facilities are essential to explore the ultra-high-energy (UHE, E$>100$ TeV) $\gamma$-ray domain and pinpoint the location of PeVatrons in the Galaxy. The Southern Wide-field Gamma-ray Observatory (SWGO) is proposed next-generation ground-based extensive air shower observatory planned for construction in the Southern Hemisphere, which holds great scientific potential for UHE observations. In this study, we investigate the expected potential of SWGO to search for hadronic PeVatrons, based on the publicly available preliminary SWGO straw-man instrument response functions (IRFs). By using these straw-man IRFs, it can be shown that the SWGO detection of $\gamma$-ray spectral cutoffs between 30 TeV and 100 TeV, at a 95% confidence level, is possible for faint $\gamma$-ray sources of $\sim$5 mCrab given that the spectral index is hard ($\Gamma \lesssim$ 2.0), while spectral cutoffs from softer sources with $\Gamma \cong$2.3 can be detected for sources brighter than $\sim 11-$12 mCrab. The reconstructed SWGO PeVatron detection maps demonstrate that the future SWGO experiment can probe large parts of the investigated PeVatron parameter space, providing a robust detection and/or rejection of presence of spectral signatures associated with hadronic PeVatrons. A dedicated study on the promising Southern-sky PeVatron candidates, the Galactic Center region, Westerlund 1, HESS J1702$-$420 and HESS J1641$-$463, shows that the SWGO will have a great potential to confirm or exclude PeVatron nature of these candidate sources at a robust significance level after 5-years of observation. In addition, it is shown that controlling systematic errors will be necessary to reach full potential of the SWGO experiment for PeVatron searches.