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 $4.0\, \sigma$ and $4.4\, \sigma$ levels above 25 TeV and 100 TeV, respectively, in units of Gaussian standard deviation $\sigma$. The energy spectrum measured between $40\, { \rm TeV} < E < 320\, { \rm TeV}$ for the first time is described with a simple power-law function of ${ \rm d}N/{ \rm d}E = (2.86 \pm 1.44) \times 10^{ -16}(E/40\, { \rm TeV})^{ -2.24 \pm 0.41}\, { \rm TeV}^{ -1}\, { \rm cm}^{ -2}\, { \rm s}^{ -1}$. The gamma-ray energy spectrum from the sub-TeV ($E < 1\, { \rm TeV}$) to sub-PeV ($100\, { \rm TeV} < E < 1\, { \rm PeV}$) ranges including the results of previous studies can be modeled with the leptonic scenario, 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 $E_{ \rm p\, cut}$, cut is estimated at ${ \rm log}_{ 10}(E_{ \rm p,\, cut}/{ \rm TeV}) = 3.73^{ +2.98}_{ -0.66}$, 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 for a Galactic PeV cosmic-ray accelerator, PeVatron.
Categories: astro-ph.HE