# The LHAASO PeVatron Bright Sky: What We Learned
## 1 Introduction
### Status of the Field after the LHAASO Results  
The recent LHAASO discovery of several galactic sources emitting UHE \(\gamma\)-rays [43; 44; 45] represents a strong breakthrough in the context of PeVatron research. Most of the sources seem to correlate to pulsars, and/or their nebulae, PWNe (e.g., the Crab Nebula for all), a class of well known leptonic accelerators. These observations indicate the presence at these sites of ultra-relativistic electrons with energies reaching at least a few \(10^{15}\) eV. As a consequence, the \(\gamma\)-ray detection at UHEs cannot itself be considered proof of hadronic acceleration. This challenges the definition of \"PeVatron\" itself. In this work, we will generically call \"PeVatron\" an object capable of accelerating particles (hadrons or leptons) up to the PeV (=\(10^{15}\) eV) range (and emitting \(\gamma\)-ray above 100 TeV). Consequently, to indicate a source that specifically accelerates hadrons (CRs), we need to use the term \"hadronic PeVatron\". The LHAASO results also suggest that many classes of sources can accelerate CRs up to PeV energies: SNRs, MSCs, and maybe also the PWNe (see [46], and references therein). In the case of PWNe, there is also another complication: the standard first-order Fermi acceleration mechanism, underpinning diffusive shock acceleration (DSA) theory, may be not the main one (see [47; 48], for a review) and magnetic reconnection (MR) may be a valid alternative, even if simulations suggest that it may be a process producing impulsive events (flares) but not a stable VHE emission [49; 50; 51]. This discussion, however, is beyond the aims of this review. Actually, some of the LHAASO PeV detection regions could be correlated with SNRs, keeping open the possibility of having PeV emissions from this kind of source, even after their 100 yrs [52; 53; 54; 55]. Several studies are in progress to establish a \"look up table\" of parameters useful for future instruments to distinguish which SNRs are hadronic [56; 57]. The association of VHE/UHE LHAASO emissions with a determined kind of source in the observed region is challenging, due to the very low angular resolution of LHAASO and similar extended air shower (EAS) arrays. For this reason, future imaging atmospheric Cherenkov telescopes (IACTs) such as ASTRI Mini-Array [58; 59; 60; 61; 62], and CTA [63] will make a difference (see Section 4 and Figure 17, right). The LHAASO results triggered several studies on the constraints entailed by potential neutrino emissions on the \(\gamma\)-ray fluxes from the candidate PeVatron sources. In [64], the authors exploited the IceCube measurements in the surrounding of the LHAASO sources, in order to constrain their possible hadronic contribution; and in their subsequent paper [35], the same authors carried out a Bayesian analysis on the 10-year IceCube data (combined with the ANTARES [65] ones) with the same aim. The results obtained with the two approaches were very similar and can be summarized as showing the impossibility of strong constraints on the LHAASO sources (apart from the Crab) with the current instruments. These results were also confirmed by the search for neutrinos from the 12 LHAASO sources with 11 yrs of track-like events (neutrino colliding with matter in or near the detector, resulting in a HE muon that traveled a long distance) from the IceCube Collaboration [66]. In this latter work, the authors also performed a stacking analysis combining (1) all LHAASO sources, (2) LHAASO sources with SNRs as potential TeV counterparts, (3) LHAASO sources with PWNe as potential TeV counterparts. Even in this case, with the strong assumption that all of the flux measured by LHAASO is hadronic, there were no significant detection, but a 90% UL on the predicted hadronic flux. This is an indication that there is a low chance that all six sources with a SNR as candidate actually are SNRs and the same is valid for the nine possible PWNes (see Figure 2).