1LHAASO J1852+0050u: GeV-100TeV Gamma-ray emission Powered by Star-forming Region?

Abstract: Star-forming regions (SFRs), including HII regions, have recently attracted significant attention as potential sites of particle acceleration capable of producing PeV cosmic rays, i.e. as potential Galactic PeVatrons. Yet, SFRs known as candidate PeVatrons are still very rare. Here we report a highly likely physical association between the UHE gamma-ray source 1LHAASO J1852+0050u and coincident star-forming regions. Using $\sim$4 years of LHAASO data, the extended source 1LHAASO J1852+0050u (called J1852 in this study) was reanalyzed with a significance of $\sim$13$σ$ and 39%-containment radius of 0.35$°$. This extended source projectively covers dozens of HII regions and an energetic pulsar PSR J1853+0056. We reanalyzed $\sim$16 years of Fermi-LAT data and found a GeV source (named SrcAG) coincident with the LHAASO source J1852. The CO-line observation shows a molecular clump which coincides with the gamma-ray sources and is related with the ultra-compact HII region G34.26+0.15 at the distance of $\sim$3.3 kpc. Fitting to the spectral energy distribution indicates that PSR J1853+0056 cannot afford the observed gamma-ray flux either for J1852 or SrcAG. Although the contribution from hidden pulsars to the gamma-ray emission could not be excluded, it is most likely that the GeV-100TeV gamma-ray emission is dominantly powered by SFR through p-p hadronic interaction between the protons accelerated in the SFR and MCs: the GeV emission is ascribed to the protons accelerated by protostars' activities, while the TeV emission ascribed to the protons accelerated by massive stars in the SFR.