Speaker
Description
It is difficult to identify hadronic PeVatrons (the PeV particle accelerator) from the ultra-high-energy (UHE, E>100TeV) gamma-ray sources, which is however crucial in revealing the origin of cosmic rays. As an endeavor in this regard, we focus in this work on the UHE gamma-ray source 1LHAASO J1857+0203u, which may associate with the supernova remnant (SNR) G35.6−0.4 and H II region G35.6−0.5. We analyze LHAASO KM2A and WCDA data, and report the point-like nature with a significance of 10.1σ above 100 TeV revealed by KM2A. While in 1-30 TeV band, the energy window of the WCDA detector , it shows extension with $r_{39}=0.18$ deg. The spectra measured by WCDA and KM2A can be smoothly connected, with a flux F(>1 TeV)=5.2e-12 erg/cm2/s. Based on the calculation, it is unlikely that the gamma-rays are from clouds illuminated by protons escaped from SNR G35.6-0.4. In the scenario that HII region can accelerate particles to the UHE band, the spectra is well explained by the hadronic process with an index of ~2.0 and a cutoff energy of 260 TeV. However, the putative PWN model can not be ruled out.
