# The LHAASO PeVatron Bright Sky: What We Learned
## 1 Introduction
### Status of the Field after the LHAASO Results
In all the works, however, the great potential represented by future instruments is stressed, such as IceCube-Gen2, to detect neutrino emissions by LHAASO PeVatrons, in the cases where there are hadronic PeVatrons (see Section 4). Several theoretical works have been developed after the LHAASO results, analyzing which kinds of source are able to satisfy the requirements needed to explain the CR density in our galaxies, in spite of the acceleration mechanism at the origin (DSA is the main source, but there is the magnetic reconnection that can contribute in microquasar jets or to the wind of the PWNe) [5; 67; 68; 69; 70]. One of the main hypotheses so far is that, since the CR spectrum in the energy range around the \"knee\" shows various features, maybe we can have different contributions from different kinds of sources at different energies ([71] and Figure 3). A parallel analysis of \(\gamma\)-ray and neutrinos from different source types can give us the key to interpreting the recent results from LHAASO and from the other VHE-UHE \(\gamma\)-ray instruments [42; 64; 66; 72], in order to discern hadronic from leptonic accelerators. This kind of analysis is also important for comparing known and well-studied sources with the same types of candidate sources of PeVatrons, to understand which physical conditions are behind the differences. We can summarize the century of studies into the CR context in the following way:  
* CRs were discovered in 1912 but, despite the enormous efforts made in recent years, the primary three questions about their origin still need to be clarified: what are their sources, how are they accelerated, and how do they propagate? * Two direct pieces of evidence were identified in \(\gamma\)-rays as a signature of sources of galactic CRs: the \"pion bump\" below 100 MeV, due to the \(\pi^{0}\) decay, and \(\gamma\)-ray emissions at E \(>\) 100 TeV. * In the standard paradigm, the main candidates for galactic CR acceleration are SNRs, mainly for energetic reasons. In spite of the evidence of the \"pion bump\" in some of them, no SNRs have been detected at E \(>\) 100 TeV, and the hypothesis that other kinds of source could contribute to CR acceleration emerged. Figure 2: Figures from [66], where the 90% flux upper limits on neutrino emissions at 50 TeV from LHAASO sources that could be associated with SNRs (**left**) and with PWNe (**right**) are indicated. The orange line represents the equal neutrino flux on Earth (the relative weight of the sources is 1/N), and the blue line represents the neutrino flux proportional to the \(\gamma\)-ray flux (relative weight based on the \(\gamma\)-ray flux of every source). The red line is the hadronic flux provided by the assumption that the entire \(\gamma\)-ray flux is of hadronic origin. * The first observational evidence of VHE emissions without the sign of a cutoff from MSCs, microquasars, and PWNe confirmed this latter hypothesis and questioned the emissions at E \(>\) 100 TeV as the \"smoking gun\" of hadronic acceleration. * The detection of 12 Galactic PeVatrons by LHAASO confirmed that sources other from SNRs can accelerate CRs and that electrons can emit UHE \(\gamma\)-ray. Consequently, we need further help to understand which sources are really CR accelerators. * Neutrino detection and better morphological reconstruction are fundamental tools to achieve this aim, and future instruments can be of great help. Starting from this context, we think that a summary of the work performed on the LHAASO sources after the publication of the 12 PeVatron paper [43] could be very useful to the scientific community, and also for future instruments, to determine the right action plan. We are aware that other instruments before LHAASO, e.g., HAWC and MAGIC, obtained results that hinted at what LHAASO revealed subsequently. However, we think the results from LHAASO were a breakthrough for two main reasons: the extension by an order of magnitude of the energy range, and the relatively large number of sources.