# The LHAASO PeVatron Bright Sky: What We Learned
## 3 Overview of the 12 LHAASO Sources
### LHAASO J1825-1326  
The candidate PeVatron LHAASO J1825-1326 is one of the sources (the others are the Crab, LHAASO J1908+0621 and LHAASO J2226+6057) detected with the highest significance at E \(>100\) TeV (\(\sigma=16.4\)) and for which there is a UHE SED without any hint of a cutoff (see Figure 8, bottom panel, and paper [43]). Its maximum energy is \(E_{M}\approx 420\) TeV and the gradual steepening at the highest energies may be due to photon-photon absorption [43]. Its potential TeV counterparts are HESS J1825-137/2 HWC J1825-134 and HESS J1826-130, both PWNe in a region smaller than the LHAASO angular resolution (see Figure 8, top panel).  
HESS J1825-137 is the name of the PWN associated with the PSR B1823-13, revealed by the first Galactic Plane Survey of HESS [140] and is one of the brightest and most extended sources in the galaxy at VHE, with an intrinsic diameter of about 100 pc [22; 141]. This was also detected by HAWC as a unique extended region, eHWC J1825-134 [117], then resolved into three different \(\gamma\)-ray emitting components (HAWC J1825-138, HAWC J1826-128, and HAWC J1825-134). In particular, HAWC J1825-134 is at only 0.03\({}^{\circ}\) for the LHAASO source (see Figure 8 top right) and its spectrum extends beyond 100 TeV without a cutoff, whereas HAWC J1825-138 seems to confirm the spectral behavior of HESS J1825-137 [141], with a cutoff below 100 TeV. We cannot exclude that HESS J1825-137 is actually a composition of two different TeV sources. This HESS \(\gamma\)-ray source shows a strong morphological dependence at GeV and TeV energies [142; 143], and the asymmetry of the nebula in the X-ray band [144] could be due to the reverberation phase (interaction of the termination shock with the parent SNR reverse shock) and/or due to the presence of an MC in the surroundings [145]. The extraordinary extension of this source makes it a possible candidate TeV halo [146], despite it not being possible to explain it within the standard dynamics of the PWN [147].  
Another one the three HAWC resolved sources, HAWC J1826-128, is detected up to 100 TeV and is spatially coincident with HESS J1826-130 [99; 148], the other potential TeV counterpart of the LHAASO PeVatron candidate, and both sources seem to be related with the \"Eel\" PWN11 (PWN G18.5-0.4) [149]. HAWC J1826-128 was detected in X-ray and \(\gamma\)-ray but not in the radio band, a strange peculiarity compared to other similar PWNe. In the same field, there is also the very poorly known SNR G18.45-0.42 [150], which cannot be ruled out as the counterpart of HESS J1826-130. According to the developed models, the leptonic nature of this emission is favored [149].  
The LHAASO angular resolution cannot resolve the region at the origin of the detected emission, consequently we cannot exclude that this PeVatron emission is due to HESS J1826-130 instead of HESS J1825-137. Actually, the spectrum of LHAASO J1825-1326 is one order of magnitude above the spectrum of HESS J1825-137 [22] and the associated HAWC J1825-138 [141] (see Figure 8, bottom). This could be due to the fact that all three resolved HAWC sources (HAWC J1825-138, HAWC J1826-128, and HAWC J1825-134) can contribute to the LHAASO TeV region (see their VHE spectra shown in [141]). This implies that a  
Figure 7: LHAASO J0534+2202. \(\gamma\)-ray spectrum of the Crab nebula with all data points collected to date and fitted with one of the models that takes into account the contribution of a hadronic component at the highest energies [Figure from [138]].  
deeper analysis of this TeV \(\gamma\)-ray bright LHAASO region is necessary. It is clear that the better angular resolution of the ASTRI Mini-Array and CTA will be fundamental in order to resolve this interesting region.  
In the IceCube neutrino analysis carried out by [64] (see Section 1.2), LHAASO J1825-1326 was constrained to being leptonic dominant up to 200 TeV. The Bayesian approach used in [35] could not constrain this source, stressing how these neutrino-based estimations are strongly biased by statistical methods.