부산대학교 도서관

Gamma rays from HESS J1849−000, a middle-aged TeV pulsar wind nebula (PWN), are observed by the Tibet air shower array and the muon detector array. The detection significance of gamma rays reaches 4.0 σ and 4.4 σ levels above 25 TeV and 100 TeV, respectively, in units of the Gaussian standard deviation σ . The energy spectrum measured between 40 TeV < E < 320 TeV for the first time is described with a simple power-law function of ${dN}/{dE}={(2.86\pm 1.44)\times {10}^{-16}(E/40\,\mathrm{TeV})}^{-2.24\pm 0.41}\,{\mathrm{TeV}}^{-1}\,{\mathrm{cm}}^{-2}\,{{\rm{s}}}^{-1}$ . The gamma-ray energy spectrum from the sub-TeV ( E < 1 TeV) to sub-PeV (100 TeV < E < 1 PeV) ranges, including the results of previous studies, can be modeled with the leptonic scenario, i.e., inverse Compton scattering by high-energy electrons accelerated by the PWN of PSR J1849−0001. On the other hand, the gamma-ray energy spectrum can also be modeled with the hadronic scenario in which gamma rays are generated from the decay of neutral pions produced by collisions between accelerated cosmic-ray protons and the ambient molecular cloud found in the gamma-ray-emitting region. The cutoff energy of cosmic-ray protons E _p,cut is estimated as ${\mathrm{log}}_{10}({E}_{{\rm{p}},\mathrm{cut}}/\mathrm{TeV})={3.73}_{-0.66}^{+2.98}$ , suggesting that protons are accelerated up to the PeV energy range. Our study thus proposes that HESS J1849−000 should be further investigated as a new candidate as a Galactic PeV cosmic-ray accelerator, or “PeVatron.”