HESS J1843$-$033 is a very-high-energy gamma-ray source whose origin remains unidentified. This work presents, for the first time, the energy spectrum of gamma rays beyond $100\, { \rm TeV}$ from the HESS J1843$-$033 region using the data recorded by the Tibet air shower array and its underground muon detector array. A gamma-ray source with an extension of $0.34^{ \circ} \pm 0.12^{ \circ}$ is successfully detected above $25\, { \rm TeV}$ at $(\alpha,\, \delta) = (281.09^{ \circ}\pm 0.10^{ \circ},\, -3.76^{ \circ}\pm 0.09^{ \circ})$ near HESS J1843$-$033 with a statistical significance of $6.2\, \sigma$, and the source is named TASG J1844$-$038. The position of TASG J1844$-$038 is consistent with those of HESS J1843$-$033, eHWC J1842$-$035, and LHAASO J1843$-$0338. The measured gamma-ray energy spectrum in $25\, { \rm TeV} < E < 130\, { \rm TeV}$ is described with ${ \rm d}N/{ \rm d}E = (9.70\pm 1.89)\times 10^{ -16} (E/40\, { \rm TeV})^{ -3.26\pm 0.30}\, { \rm TeV}^{ -1} { \rm cm}^{ -2} { \rm s}^{ -1}$, and the spectral fit to the combined spectra of HESS J1843$-$033, LHAASO J1843$-$0338, and TASG J1844$-$038 implies the existence of a cutoff at $49.5\pm 9.0\, { \rm TeV}$. Associations of TASG J1844-038 with SNR G28.6$-$0.1 and PSR J1844-0346 are also discussed in detail for the first time.
Categories: astro-ph.HE